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authorAnton Arapov <anton@redhat.com>2012-04-16 10:05:28 +0200
committerAnton Arapov <anton@redhat.com>2012-04-16 10:05:28 +0200
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tree93d1b7e2cfcdf473d8d4ff3ad141fa864f8491f6 /Documentation/virtual/kvm
parentedd4be777c953e5faafc80d091d3084b4343f5d3 (diff)
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fedora kernel: d9aad82f3319f3cfd1aebc01234254ef0c37ad84v3.3.2-1
Signed-off-by: Anton Arapov <anton@redhat.com>
Diffstat (limited to 'Documentation/virtual/kvm')
-rw-r--r--Documentation/virtual/kvm/api.txt1743
-rw-r--r--Documentation/virtual/kvm/cpuid.txt45
-rw-r--r--Documentation/virtual/kvm/locking.txt25
-rw-r--r--Documentation/virtual/kvm/mmu.txt366
-rw-r--r--Documentation/virtual/kvm/msr.txt221
-rw-r--r--Documentation/virtual/kvm/nested-vmx.txt251
-rw-r--r--Documentation/virtual/kvm/ppc-pv.txt198
-rw-r--r--Documentation/virtual/kvm/review-checklist.txt38
-rw-r--r--Documentation/virtual/kvm/timekeeping.txt612
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+The Definitive KVM (Kernel-based Virtual Machine) API Documentation
+===================================================================
+
+1. General description
+
+The kvm API is a set of ioctls that are issued to control various aspects
+of a virtual machine. The ioctls belong to three classes
+
+ - System ioctls: These query and set global attributes which affect the
+ whole kvm subsystem. In addition a system ioctl is used to create
+ virtual machines
+
+ - VM ioctls: These query and set attributes that affect an entire virtual
+ machine, for example memory layout. In addition a VM ioctl is used to
+ create virtual cpus (vcpus).
+
+ Only run VM ioctls from the same process (address space) that was used
+ to create the VM.
+
+ - vcpu ioctls: These query and set attributes that control the operation
+ of a single virtual cpu.
+
+ Only run vcpu ioctls from the same thread that was used to create the
+ vcpu.
+
+2. File descriptors
+
+The kvm API is centered around file descriptors. An initial
+open("/dev/kvm") obtains a handle to the kvm subsystem; this handle
+can be used to issue system ioctls. A KVM_CREATE_VM ioctl on this
+handle will create a VM file descriptor which can be used to issue VM
+ioctls. A KVM_CREATE_VCPU ioctl on a VM fd will create a virtual cpu
+and return a file descriptor pointing to it. Finally, ioctls on a vcpu
+fd can be used to control the vcpu, including the important task of
+actually running guest code.
+
+In general file descriptors can be migrated among processes by means
+of fork() and the SCM_RIGHTS facility of unix domain socket. These
+kinds of tricks are explicitly not supported by kvm. While they will
+not cause harm to the host, their actual behavior is not guaranteed by
+the API. The only supported use is one virtual machine per process,
+and one vcpu per thread.
+
+3. Extensions
+
+As of Linux 2.6.22, the KVM ABI has been stabilized: no backward
+incompatible change are allowed. However, there is an extension
+facility that allows backward-compatible extensions to the API to be
+queried and used.
+
+The extension mechanism is not based on on the Linux version number.
+Instead, kvm defines extension identifiers and a facility to query
+whether a particular extension identifier is available. If it is, a
+set of ioctls is available for application use.
+
+4. API description
+
+This section describes ioctls that can be used to control kvm guests.
+For each ioctl, the following information is provided along with a
+description:
+
+ Capability: which KVM extension provides this ioctl. Can be 'basic',
+ which means that is will be provided by any kernel that supports
+ API version 12 (see section 4.1), or a KVM_CAP_xyz constant, which
+ means availability needs to be checked with KVM_CHECK_EXTENSION
+ (see section 4.4).
+
+ Architectures: which instruction set architectures provide this ioctl.
+ x86 includes both i386 and x86_64.
+
+ Type: system, vm, or vcpu.
+
+ Parameters: what parameters are accepted by the ioctl.
+
+ Returns: the return value. General error numbers (EBADF, ENOMEM, EINVAL)
+ are not detailed, but errors with specific meanings are.
+
+4.1 KVM_GET_API_VERSION
+
+Capability: basic
+Architectures: all
+Type: system ioctl
+Parameters: none
+Returns: the constant KVM_API_VERSION (=12)
+
+This identifies the API version as the stable kvm API. It is not
+expected that this number will change. However, Linux 2.6.20 and
+2.6.21 report earlier versions; these are not documented and not
+supported. Applications should refuse to run if KVM_GET_API_VERSION
+returns a value other than 12. If this check passes, all ioctls
+described as 'basic' will be available.
+
+4.2 KVM_CREATE_VM
+
+Capability: basic
+Architectures: all
+Type: system ioctl
+Parameters: none
+Returns: a VM fd that can be used to control the new virtual machine.
+
+The new VM has no virtual cpus and no memory. An mmap() of a VM fd
+will access the virtual machine's physical address space; offset zero
+corresponds to guest physical address zero. Use of mmap() on a VM fd
+is discouraged if userspace memory allocation (KVM_CAP_USER_MEMORY) is
+available.
+
+4.3 KVM_GET_MSR_INDEX_LIST
+
+Capability: basic
+Architectures: x86
+Type: system
+Parameters: struct kvm_msr_list (in/out)
+Returns: 0 on success; -1 on error
+Errors:
+ E2BIG: the msr index list is to be to fit in the array specified by
+ the user.
+
+struct kvm_msr_list {
+ __u32 nmsrs; /* number of msrs in entries */
+ __u32 indices[0];
+};
+
+This ioctl returns the guest msrs that are supported. The list varies
+by kvm version and host processor, but does not change otherwise. The
+user fills in the size of the indices array in nmsrs, and in return
+kvm adjusts nmsrs to reflect the actual number of msrs and fills in
+the indices array with their numbers.
+
+Note: if kvm indicates supports MCE (KVM_CAP_MCE), then the MCE bank MSRs are
+not returned in the MSR list, as different vcpus can have a different number
+of banks, as set via the KVM_X86_SETUP_MCE ioctl.
+
+4.4 KVM_CHECK_EXTENSION
+
+Capability: basic
+Architectures: all
+Type: system ioctl
+Parameters: extension identifier (KVM_CAP_*)
+Returns: 0 if unsupported; 1 (or some other positive integer) if supported
+
+The API allows the application to query about extensions to the core
+kvm API. Userspace passes an extension identifier (an integer) and
+receives an integer that describes the extension availability.
+Generally 0 means no and 1 means yes, but some extensions may report
+additional information in the integer return value.
+
+4.5 KVM_GET_VCPU_MMAP_SIZE
+
+Capability: basic
+Architectures: all
+Type: system ioctl
+Parameters: none
+Returns: size of vcpu mmap area, in bytes
+
+The KVM_RUN ioctl (cf.) communicates with userspace via a shared
+memory region. This ioctl returns the size of that region. See the
+KVM_RUN documentation for details.
+
+4.6 KVM_SET_MEMORY_REGION
+
+Capability: basic
+Architectures: all
+Type: vm ioctl
+Parameters: struct kvm_memory_region (in)
+Returns: 0 on success, -1 on error
+
+This ioctl is obsolete and has been removed.
+
+4.7 KVM_CREATE_VCPU
+
+Capability: basic
+Architectures: all
+Type: vm ioctl
+Parameters: vcpu id (apic id on x86)
+Returns: vcpu fd on success, -1 on error
+
+This API adds a vcpu to a virtual machine. The vcpu id is a small integer
+in the range [0, max_vcpus).
+
+The recommended max_vcpus value can be retrieved using the KVM_CAP_NR_VCPUS of
+the KVM_CHECK_EXTENSION ioctl() at run-time.
+The maximum possible value for max_vcpus can be retrieved using the
+KVM_CAP_MAX_VCPUS of the KVM_CHECK_EXTENSION ioctl() at run-time.
+
+If the KVM_CAP_NR_VCPUS does not exist, you should assume that max_vcpus is 4
+cpus max.
+If the KVM_CAP_MAX_VCPUS does not exist, you should assume that max_vcpus is
+same as the value returned from KVM_CAP_NR_VCPUS.
+
+On powerpc using book3s_hv mode, the vcpus are mapped onto virtual
+threads in one or more virtual CPU cores. (This is because the
+hardware requires all the hardware threads in a CPU core to be in the
+same partition.) The KVM_CAP_PPC_SMT capability indicates the number
+of vcpus per virtual core (vcore). The vcore id is obtained by
+dividing the vcpu id by the number of vcpus per vcore. The vcpus in a
+given vcore will always be in the same physical core as each other
+(though that might be a different physical core from time to time).
+Userspace can control the threading (SMT) mode of the guest by its
+allocation of vcpu ids. For example, if userspace wants
+single-threaded guest vcpus, it should make all vcpu ids be a multiple
+of the number of vcpus per vcore.
+
+On powerpc using book3s_hv mode, the vcpus are mapped onto virtual
+threads in one or more virtual CPU cores. (This is because the
+hardware requires all the hardware threads in a CPU core to be in the
+same partition.) The KVM_CAP_PPC_SMT capability indicates the number
+of vcpus per virtual core (vcore). The vcore id is obtained by
+dividing the vcpu id by the number of vcpus per vcore. The vcpus in a
+given vcore will always be in the same physical core as each other
+(though that might be a different physical core from time to time).
+Userspace can control the threading (SMT) mode of the guest by its
+allocation of vcpu ids. For example, if userspace wants
+single-threaded guest vcpus, it should make all vcpu ids be a multiple
+of the number of vcpus per vcore.
+
+4.8 KVM_GET_DIRTY_LOG (vm ioctl)
+
+Capability: basic
+Architectures: x86
+Type: vm ioctl
+Parameters: struct kvm_dirty_log (in/out)
+Returns: 0 on success, -1 on error
+
+/* for KVM_GET_DIRTY_LOG */
+struct kvm_dirty_log {
+ __u32 slot;
+ __u32 padding;
+ union {
+ void __user *dirty_bitmap; /* one bit per page */
+ __u64 padding;
+ };
+};
+
+Given a memory slot, return a bitmap containing any pages dirtied
+since the last call to this ioctl. Bit 0 is the first page in the
+memory slot. Ensure the entire structure is cleared to avoid padding
+issues.
+
+4.9 KVM_SET_MEMORY_ALIAS
+
+Capability: basic
+Architectures: x86
+Type: vm ioctl
+Parameters: struct kvm_memory_alias (in)
+Returns: 0 (success), -1 (error)
+
+This ioctl is obsolete and has been removed.
+
+4.10 KVM_RUN
+
+Capability: basic
+Architectures: all
+Type: vcpu ioctl
+Parameters: none
+Returns: 0 on success, -1 on error
+Errors:
+ EINTR: an unmasked signal is pending
+
+This ioctl is used to run a guest virtual cpu. While there are no
+explicit parameters, there is an implicit parameter block that can be
+obtained by mmap()ing the vcpu fd at offset 0, with the size given by
+KVM_GET_VCPU_MMAP_SIZE. The parameter block is formatted as a 'struct
+kvm_run' (see below).
+
+4.11 KVM_GET_REGS
+
+Capability: basic
+Architectures: all
+Type: vcpu ioctl
+Parameters: struct kvm_regs (out)
+Returns: 0 on success, -1 on error
+
+Reads the general purpose registers from the vcpu.
+
+/* x86 */
+struct kvm_regs {
+ /* out (KVM_GET_REGS) / in (KVM_SET_REGS) */
+ __u64 rax, rbx, rcx, rdx;
+ __u64 rsi, rdi, rsp, rbp;
+ __u64 r8, r9, r10, r11;
+ __u64 r12, r13, r14, r15;
+ __u64 rip, rflags;
+};
+
+4.12 KVM_SET_REGS
+
+Capability: basic
+Architectures: all
+Type: vcpu ioctl
+Parameters: struct kvm_regs (in)
+Returns: 0 on success, -1 on error
+
+Writes the general purpose registers into the vcpu.
+
+See KVM_GET_REGS for the data structure.
+
+4.13 KVM_GET_SREGS
+
+Capability: basic
+Architectures: x86, ppc
+Type: vcpu ioctl
+Parameters: struct kvm_sregs (out)
+Returns: 0 on success, -1 on error
+
+Reads special registers from the vcpu.
+
+/* x86 */
+struct kvm_sregs {
+ struct kvm_segment cs, ds, es, fs, gs, ss;
+ struct kvm_segment tr, ldt;
+ struct kvm_dtable gdt, idt;
+ __u64 cr0, cr2, cr3, cr4, cr8;
+ __u64 efer;
+ __u64 apic_base;
+ __u64 interrupt_bitmap[(KVM_NR_INTERRUPTS + 63) / 64];
+};
+
+/* ppc -- see arch/powerpc/include/asm/kvm.h */
+
+interrupt_bitmap is a bitmap of pending external interrupts. At most
+one bit may be set. This interrupt has been acknowledged by the APIC
+but not yet injected into the cpu core.
+
+4.14 KVM_SET_SREGS
+
+Capability: basic
+Architectures: x86, ppc
+Type: vcpu ioctl
+Parameters: struct kvm_sregs (in)
+Returns: 0 on success, -1 on error
+
+Writes special registers into the vcpu. See KVM_GET_SREGS for the
+data structures.
+
+4.15 KVM_TRANSLATE
+
+Capability: basic
+Architectures: x86
+Type: vcpu ioctl
+Parameters: struct kvm_translation (in/out)
+Returns: 0 on success, -1 on error
+
+Translates a virtual address according to the vcpu's current address
+translation mode.
+
+struct kvm_translation {
+ /* in */
+ __u64 linear_address;
+
+ /* out */
+ __u64 physical_address;
+ __u8 valid;
+ __u8 writeable;
+ __u8 usermode;
+ __u8 pad[5];
+};
+
+4.16 KVM_INTERRUPT
+
+Capability: basic
+Architectures: x86, ppc
+Type: vcpu ioctl
+Parameters: struct kvm_interrupt (in)
+Returns: 0 on success, -1 on error
+
+Queues a hardware interrupt vector to be injected. This is only
+useful if in-kernel local APIC or equivalent is not used.
+
+/* for KVM_INTERRUPT */
+struct kvm_interrupt {
+ /* in */
+ __u32 irq;
+};
+
+X86:
+
+Note 'irq' is an interrupt vector, not an interrupt pin or line.
+
+PPC:
+
+Queues an external interrupt to be injected. This ioctl is overleaded
+with 3 different irq values:
+
+a) KVM_INTERRUPT_SET
+
+ This injects an edge type external interrupt into the guest once it's ready
+ to receive interrupts. When injected, the interrupt is done.
+
+b) KVM_INTERRUPT_UNSET
+
+ This unsets any pending interrupt.
+
+ Only available with KVM_CAP_PPC_UNSET_IRQ.
+
+c) KVM_INTERRUPT_SET_LEVEL
+
+ This injects a level type external interrupt into the guest context. The
+ interrupt stays pending until a specific ioctl with KVM_INTERRUPT_UNSET
+ is triggered.
+
+ Only available with KVM_CAP_PPC_IRQ_LEVEL.
+
+Note that any value for 'irq' other than the ones stated above is invalid
+and incurs unexpected behavior.
+
+4.17 KVM_DEBUG_GUEST
+
+Capability: basic
+Architectures: none
+Type: vcpu ioctl
+Parameters: none)
+Returns: -1 on error
+
+Support for this has been removed. Use KVM_SET_GUEST_DEBUG instead.
+
+4.18 KVM_GET_MSRS
+
+Capability: basic
+Architectures: x86
+Type: vcpu ioctl
+Parameters: struct kvm_msrs (in/out)
+Returns: 0 on success, -1 on error
+
+Reads model-specific registers from the vcpu. Supported msr indices can
+be obtained using KVM_GET_MSR_INDEX_LIST.
+
+struct kvm_msrs {
+ __u32 nmsrs; /* number of msrs in entries */
+ __u32 pad;
+
+ struct kvm_msr_entry entries[0];
+};
+
+struct kvm_msr_entry {
+ __u32 index;
+ __u32 reserved;
+ __u64 data;
+};
+
+Application code should set the 'nmsrs' member (which indicates the
+size of the entries array) and the 'index' member of each array entry.
+kvm will fill in the 'data' member.
+
+4.19 KVM_SET_MSRS
+
+Capability: basic
+Architectures: x86
+Type: vcpu ioctl
+Parameters: struct kvm_msrs (in)
+Returns: 0 on success, -1 on error
+
+Writes model-specific registers to the vcpu. See KVM_GET_MSRS for the
+data structures.
+
+Application code should set the 'nmsrs' member (which indicates the
+size of the entries array), and the 'index' and 'data' members of each
+array entry.
+
+4.20 KVM_SET_CPUID
+
+Capability: basic
+Architectures: x86
+Type: vcpu ioctl
+Parameters: struct kvm_cpuid (in)
+Returns: 0 on success, -1 on error
+
+Defines the vcpu responses to the cpuid instruction. Applications
+should use the KVM_SET_CPUID2 ioctl if available.
+
+
+struct kvm_cpuid_entry {
+ __u32 function;
+ __u32 eax;
+ __u32 ebx;
+ __u32 ecx;
+ __u32 edx;
+ __u32 padding;
+};
+
+/* for KVM_SET_CPUID */
+struct kvm_cpuid {
+ __u32 nent;
+ __u32 padding;
+ struct kvm_cpuid_entry entries[0];
+};
+
+4.21 KVM_SET_SIGNAL_MASK
+
+Capability: basic
+Architectures: x86
+Type: vcpu ioctl
+Parameters: struct kvm_signal_mask (in)
+Returns: 0 on success, -1 on error
+
+Defines which signals are blocked during execution of KVM_RUN. This
+signal mask temporarily overrides the threads signal mask. Any
+unblocked signal received (except SIGKILL and SIGSTOP, which retain
+their traditional behaviour) will cause KVM_RUN to return with -EINTR.
+
+Note the signal will only be delivered if not blocked by the original
+signal mask.
+
+/* for KVM_SET_SIGNAL_MASK */
+struct kvm_signal_mask {
+ __u32 len;
+ __u8 sigset[0];
+};
+
+4.22 KVM_GET_FPU
+
+Capability: basic
+Architectures: x86
+Type: vcpu ioctl
+Parameters: struct kvm_fpu (out)
+Returns: 0 on success, -1 on error
+
+Reads the floating point state from the vcpu.
+
+/* for KVM_GET_FPU and KVM_SET_FPU */
+struct kvm_fpu {
+ __u8 fpr[8][16];
+ __u16 fcw;
+ __u16 fsw;
+ __u8 ftwx; /* in fxsave format */
+ __u8 pad1;
+ __u16 last_opcode;
+ __u64 last_ip;
+ __u64 last_dp;
+ __u8 xmm[16][16];
+ __u32 mxcsr;
+ __u32 pad2;
+};
+
+4.23 KVM_SET_FPU
+
+Capability: basic
+Architectures: x86
+Type: vcpu ioctl
+Parameters: struct kvm_fpu (in)
+Returns: 0 on success, -1 on error
+
+Writes the floating point state to the vcpu.
+
+/* for KVM_GET_FPU and KVM_SET_FPU */
+struct kvm_fpu {
+ __u8 fpr[8][16];
+ __u16 fcw;
+ __u16 fsw;
+ __u8 ftwx; /* in fxsave format */
+ __u8 pad1;
+ __u16 last_opcode;
+ __u64 last_ip;
+ __u64 last_dp;
+ __u8 xmm[16][16];
+ __u32 mxcsr;
+ __u32 pad2;
+};
+
+4.24 KVM_CREATE_IRQCHIP
+
+Capability: KVM_CAP_IRQCHIP
+Architectures: x86, ia64
+Type: vm ioctl
+Parameters: none
+Returns: 0 on success, -1 on error
+
+Creates an interrupt controller model in the kernel. On x86, creates a virtual
+ioapic, a virtual PIC (two PICs, nested), and sets up future vcpus to have a
+local APIC. IRQ routing for GSIs 0-15 is set to both PIC and IOAPIC; GSI 16-23
+only go to the IOAPIC. On ia64, a IOSAPIC is created.
+
+4.25 KVM_IRQ_LINE
+
+Capability: KVM_CAP_IRQCHIP
+Architectures: x86, ia64
+Type: vm ioctl
+Parameters: struct kvm_irq_level
+Returns: 0 on success, -1 on error
+
+Sets the level of a GSI input to the interrupt controller model in the kernel.
+Requires that an interrupt controller model has been previously created with
+KVM_CREATE_IRQCHIP. Note that edge-triggered interrupts require the level
+to be set to 1 and then back to 0.
+
+struct kvm_irq_level {
+ union {
+ __u32 irq; /* GSI */
+ __s32 status; /* not used for KVM_IRQ_LEVEL */
+ };
+ __u32 level; /* 0 or 1 */
+};
+
+4.26 KVM_GET_IRQCHIP
+
+Capability: KVM_CAP_IRQCHIP
+Architectures: x86, ia64
+Type: vm ioctl
+Parameters: struct kvm_irqchip (in/out)
+Returns: 0 on success, -1 on error
+
+Reads the state of a kernel interrupt controller created with
+KVM_CREATE_IRQCHIP into a buffer provided by the caller.
+
+struct kvm_irqchip {
+ __u32 chip_id; /* 0 = PIC1, 1 = PIC2, 2 = IOAPIC */
+ __u32 pad;
+ union {
+ char dummy[512]; /* reserving space */
+ struct kvm_pic_state pic;
+ struct kvm_ioapic_state ioapic;
+ } chip;
+};
+
+4.27 KVM_SET_IRQCHIP
+
+Capability: KVM_CAP_IRQCHIP
+Architectures: x86, ia64
+Type: vm ioctl
+Parameters: struct kvm_irqchip (in)
+Returns: 0 on success, -1 on error
+
+Sets the state of a kernel interrupt controller created with
+KVM_CREATE_IRQCHIP from a buffer provided by the caller.
+
+struct kvm_irqchip {
+ __u32 chip_id; /* 0 = PIC1, 1 = PIC2, 2 = IOAPIC */
+ __u32 pad;
+ union {
+ char dummy[512]; /* reserving space */
+ struct kvm_pic_state pic;
+ struct kvm_ioapic_state ioapic;
+ } chip;
+};
+
+4.28 KVM_XEN_HVM_CONFIG
+
+Capability: KVM_CAP_XEN_HVM
+Architectures: x86
+Type: vm ioctl
+Parameters: struct kvm_xen_hvm_config (in)
+Returns: 0 on success, -1 on error
+
+Sets the MSR that the Xen HVM guest uses to initialize its hypercall
+page, and provides the starting address and size of the hypercall
+blobs in userspace. When the guest writes the MSR, kvm copies one
+page of a blob (32- or 64-bit, depending on the vcpu mode) to guest
+memory.
+
+struct kvm_xen_hvm_config {
+ __u32 flags;
+ __u32 msr;
+ __u64 blob_addr_32;
+ __u64 blob_addr_64;
+ __u8 blob_size_32;
+ __u8 blob_size_64;
+ __u8 pad2[30];
+};
+
+4.29 KVM_GET_CLOCK
+
+Capability: KVM_CAP_ADJUST_CLOCK
+Architectures: x86
+Type: vm ioctl
+Parameters: struct kvm_clock_data (out)
+Returns: 0 on success, -1 on error
+
+Gets the current timestamp of kvmclock as seen by the current guest. In
+conjunction with KVM_SET_CLOCK, it is used to ensure monotonicity on scenarios
+such as migration.
+
+struct kvm_clock_data {
+ __u64 clock; /* kvmclock current value */
+ __u32 flags;
+ __u32 pad[9];
+};
+
+4.30 KVM_SET_CLOCK
+
+Capability: KVM_CAP_ADJUST_CLOCK
+Architectures: x86
+Type: vm ioctl
+Parameters: struct kvm_clock_data (in)
+Returns: 0 on success, -1 on error
+
+Sets the current timestamp of kvmclock to the value specified in its parameter.
+In conjunction with KVM_GET_CLOCK, it is used to ensure monotonicity on scenarios
+such as migration.
+
+struct kvm_clock_data {
+ __u64 clock; /* kvmclock current value */
+ __u32 flags;
+ __u32 pad[9];
+};
+
+4.31 KVM_GET_VCPU_EVENTS
+
+Capability: KVM_CAP_VCPU_EVENTS
+Extended by: KVM_CAP_INTR_SHADOW
+Architectures: x86
+Type: vm ioctl
+Parameters: struct kvm_vcpu_event (out)
+Returns: 0 on success, -1 on error
+
+Gets currently pending exceptions, interrupts, and NMIs as well as related
+states of the vcpu.
+
+struct kvm_vcpu_events {
+ struct {
+ __u8 injected;
+ __u8 nr;
+ __u8 has_error_code;
+ __u8 pad;
+ __u32 error_code;
+ } exception;
+ struct {
+ __u8 injected;
+ __u8 nr;
+ __u8 soft;
+ __u8 shadow;
+ } interrupt;
+ struct {
+ __u8 injected;
+ __u8 pending;
+ __u8 masked;
+ __u8 pad;
+ } nmi;
+ __u32 sipi_vector;
+ __u32 flags;
+};
+
+KVM_VCPUEVENT_VALID_SHADOW may be set in the flags field to signal that
+interrupt.shadow contains a valid state. Otherwise, this field is undefined.
+
+4.32 KVM_SET_VCPU_EVENTS
+
+Capability: KVM_CAP_VCPU_EVENTS
+Extended by: KVM_CAP_INTR_SHADOW
+Architectures: x86
+Type: vm ioctl
+Parameters: struct kvm_vcpu_event (in)
+Returns: 0 on success, -1 on error
+
+Set pending exceptions, interrupts, and NMIs as well as related states of the
+vcpu.
+
+See KVM_GET_VCPU_EVENTS for the data structure.
+
+Fields that may be modified asynchronously by running VCPUs can be excluded
+from the update. These fields are nmi.pending and sipi_vector. Keep the
+corresponding bits in the flags field cleared to suppress overwriting the
+current in-kernel state. The bits are:
+
+KVM_VCPUEVENT_VALID_NMI_PENDING - transfer nmi.pending to the kernel
+KVM_VCPUEVENT_VALID_SIPI_VECTOR - transfer sipi_vector
+
+If KVM_CAP_INTR_SHADOW is available, KVM_VCPUEVENT_VALID_SHADOW can be set in
+the flags field to signal that interrupt.shadow contains a valid state and
+shall be written into the VCPU.
+
+4.33 KVM_GET_DEBUGREGS
+
+Capability: KVM_CAP_DEBUGREGS
+Architectures: x86
+Type: vm ioctl
+Parameters: struct kvm_debugregs (out)
+Returns: 0 on success, -1 on error
+
+Reads debug registers from the vcpu.
+
+struct kvm_debugregs {
+ __u64 db[4];
+ __u64 dr6;
+ __u64 dr7;
+ __u64 flags;
+ __u64 reserved[9];
+};
+
+4.34 KVM_SET_DEBUGREGS
+
+Capability: KVM_CAP_DEBUGREGS
+Architectures: x86
+Type: vm ioctl
+Parameters: struct kvm_debugregs (in)
+Returns: 0 on success, -1 on error
+
+Writes debug registers into the vcpu.
+
+See KVM_GET_DEBUGREGS for the data structure. The flags field is unused
+yet and must be cleared on entry.
+
+4.35 KVM_SET_USER_MEMORY_REGION
+
+Capability: KVM_CAP_USER_MEM
+Architectures: all
+Type: vm ioctl
+Parameters: struct kvm_userspace_memory_region (in)
+Returns: 0 on success, -1 on error
+
+struct kvm_userspace_memory_region {
+ __u32 slot;
+ __u32 flags;
+ __u64 guest_phys_addr;
+ __u64 memory_size; /* bytes */
+ __u64 userspace_addr; /* start of the userspace allocated memory */
+};
+
+/* for kvm_memory_region::flags */
+#define KVM_MEM_LOG_DIRTY_PAGES 1UL
+
+This ioctl allows the user to create or modify a guest physical memory
+slot. When changing an existing slot, it may be moved in the guest
+physical memory space, or its flags may be modified. It may not be
+resized. Slots may not overlap in guest physical address space.
+
+Memory for the region is taken starting at the address denoted by the
+field userspace_addr, which must point at user addressable memory for
+the entire memory slot size. Any object may back this memory, including
+anonymous memory, ordinary files, and hugetlbfs.
+
+It is recommended that the lower 21 bits of guest_phys_addr and userspace_addr
+be identical. This allows large pages in the guest to be backed by large
+pages in the host.
+
+The flags field supports just one flag, KVM_MEM_LOG_DIRTY_PAGES, which
+instructs kvm to keep track of writes to memory within the slot. See
+the KVM_GET_DIRTY_LOG ioctl.
+
+When the KVM_CAP_SYNC_MMU capability, changes in the backing of the memory
+region are automatically reflected into the guest. For example, an mmap()
+that affects the region will be made visible immediately. Another example
+is madvise(MADV_DROP).
+
+It is recommended to use this API instead of the KVM_SET_MEMORY_REGION ioctl.
+The KVM_SET_MEMORY_REGION does not allow fine grained control over memory
+allocation and is deprecated.
+
+4.36 KVM_SET_TSS_ADDR
+
+Capability: KVM_CAP_SET_TSS_ADDR
+Architectures: x86
+Type: vm ioctl
+Parameters: unsigned long tss_address (in)
+Returns: 0 on success, -1 on error
+
+This ioctl defines the physical address of a three-page region in the guest
+physical address space. The region must be within the first 4GB of the
+guest physical address space and must not conflict with any memory slot
+or any mmio address. The guest may malfunction if it accesses this memory
+region.
+
+This ioctl is required on Intel-based hosts. This is needed on Intel hardware
+because of a quirk in the virtualization implementation (see the internals
+documentation when it pops into existence).
+
+4.37 KVM_ENABLE_CAP
+
+Capability: KVM_CAP_ENABLE_CAP
+Architectures: ppc
+Type: vcpu ioctl
+Parameters: struct kvm_enable_cap (in)
+Returns: 0 on success; -1 on error
+
++Not all extensions are enabled by default. Using this ioctl the application
+can enable an extension, making it available to the guest.
+
+On systems that do not support this ioctl, it always fails. On systems that
+do support it, it only works for extensions that are supported for enablement.
+
+To check if a capability can be enabled, the KVM_CHECK_EXTENSION ioctl should
+be used.
+
+struct kvm_enable_cap {
+ /* in */
+ __u32 cap;
+
+The capability that is supposed to get enabled.
+
+ __u32 flags;
+
+A bitfield indicating future enhancements. Has to be 0 for now.
+
+ __u64 args[4];
+
+Arguments for enabling a feature. If a feature needs initial values to
+function properly, this is the place to put them.
+
+ __u8 pad[64];
+};
+
+4.38 KVM_GET_MP_STATE
+
+Capability: KVM_CAP_MP_STATE
+Architectures: x86, ia64
+Type: vcpu ioctl
+Parameters: struct kvm_mp_state (out)
+Returns: 0 on success; -1 on error
+
+struct kvm_mp_state {
+ __u32 mp_state;
+};
+
+Returns the vcpu's current "multiprocessing state" (though also valid on
+uniprocessor guests).
+
+Possible values are:
+
+ - KVM_MP_STATE_RUNNABLE: the vcpu is currently running
+ - KVM_MP_STATE_UNINITIALIZED: the vcpu is an application processor (AP)
+ which has not yet received an INIT signal
+ - KVM_MP_STATE_INIT_RECEIVED: the vcpu has received an INIT signal, and is
+ now ready for a SIPI
+ - KVM_MP_STATE_HALTED: the vcpu has executed a HLT instruction and
+ is waiting for an interrupt
+ - KVM_MP_STATE_SIPI_RECEIVED: the vcpu has just received a SIPI (vector
+ accessible via KVM_GET_VCPU_EVENTS)
+
+This ioctl is only useful after KVM_CREATE_IRQCHIP. Without an in-kernel
+irqchip, the multiprocessing state must be maintained by userspace.
+
+4.39 KVM_SET_MP_STATE
+
+Capability: KVM_CAP_MP_STATE
+Architectures: x86, ia64
+Type: vcpu ioctl
+Parameters: struct kvm_mp_state (in)
+Returns: 0 on success; -1 on error
+
+Sets the vcpu's current "multiprocessing state"; see KVM_GET_MP_STATE for
+arguments.
+
+This ioctl is only useful after KVM_CREATE_IRQCHIP. Without an in-kernel
+irqchip, the multiprocessing state must be maintained by userspace.
+
+4.40 KVM_SET_IDENTITY_MAP_ADDR
+
+Capability: KVM_CAP_SET_IDENTITY_MAP_ADDR
+Architectures: x86
+Type: vm ioctl
+Parameters: unsigned long identity (in)
+Returns: 0 on success, -1 on error
+
+This ioctl defines the physical address of a one-page region in the guest
+physical address space. The region must be within the first 4GB of the
+guest physical address space and must not conflict with any memory slot
+or any mmio address. The guest may malfunction if it accesses this memory
+region.
+
+This ioctl is required on Intel-based hosts. This is needed on Intel hardware
+because of a quirk in the virtualization implementation (see the internals
+documentation when it pops into existence).
+
+4.41 KVM_SET_BOOT_CPU_ID
+
+Capability: KVM_CAP_SET_BOOT_CPU_ID
+Architectures: x86, ia64
+Type: vm ioctl
+Parameters: unsigned long vcpu_id
+Returns: 0 on success, -1 on error
+
+Define which vcpu is the Bootstrap Processor (BSP). Values are the same
+as the vcpu id in KVM_CREATE_VCPU. If this ioctl is not called, the default
+is vcpu 0.
+
+4.42 KVM_GET_XSAVE
+
+Capability: KVM_CAP_XSAVE
+Architectures: x86
+Type: vcpu ioctl
+Parameters: struct kvm_xsave (out)
+Returns: 0 on success, -1 on error
+
+struct kvm_xsave {
+ __u32 region[1024];
+};
+
+This ioctl would copy current vcpu's xsave struct to the userspace.
+
+4.43 KVM_SET_XSAVE
+
+Capability: KVM_CAP_XSAVE
+Architectures: x86
+Type: vcpu ioctl
+Parameters: struct kvm_xsave (in)
+Returns: 0 on success, -1 on error
+
+struct kvm_xsave {
+ __u32 region[1024];
+};
+
+This ioctl would copy userspace's xsave struct to the kernel.
+
+4.44 KVM_GET_XCRS
+
+Capability: KVM_CAP_XCRS
+Architectures: x86
+Type: vcpu ioctl
+Parameters: struct kvm_xcrs (out)
+Returns: 0 on success, -1 on error
+
+struct kvm_xcr {
+ __u32 xcr;
+ __u32 reserved;
+ __u64 value;
+};
+
+struct kvm_xcrs {
+ __u32 nr_xcrs;
+ __u32 flags;
+ struct kvm_xcr xcrs[KVM_MAX_XCRS];
+ __u64 padding[16];
+};
+
+This ioctl would copy current vcpu's xcrs to the userspace.
+
+4.45 KVM_SET_XCRS
+
+Capability: KVM_CAP_XCRS
+Architectures: x86
+Type: vcpu ioctl
+Parameters: struct kvm_xcrs (in)
+Returns: 0 on success, -1 on error
+
+struct kvm_xcr {
+ __u32 xcr;
+ __u32 reserved;
+ __u64 value;
+};
+
+struct kvm_xcrs {
+ __u32 nr_xcrs;
+ __u32 flags;
+ struct kvm_xcr xcrs[KVM_MAX_XCRS];
+ __u64 padding[16];
+};
+
+This ioctl would set vcpu's xcr to the value userspace specified.
+
+4.46 KVM_GET_SUPPORTED_CPUID
+
+Capability: KVM_CAP_EXT_CPUID
+Architectures: x86
+Type: system ioctl
+Parameters: struct kvm_cpuid2 (in/out)
+Returns: 0 on success, -1 on error
+
+struct kvm_cpuid2 {
+ __u32 nent;
+ __u32 padding;
+ struct kvm_cpuid_entry2 entries[0];
+};
+
+#define KVM_CPUID_FLAG_SIGNIFCANT_INDEX 1
+#define KVM_CPUID_FLAG_STATEFUL_FUNC 2
+#define KVM_CPUID_FLAG_STATE_READ_NEXT 4
+
+struct kvm_cpuid_entry2 {
+ __u32 function;
+ __u32 index;
+ __u32 flags;
+ __u32 eax;
+ __u32 ebx;
+ __u32 ecx;
+ __u32 edx;
+ __u32 padding[3];
+};
+
+This ioctl returns x86 cpuid features which are supported by both the hardware
+and kvm. Userspace can use the information returned by this ioctl to
+construct cpuid information (for KVM_SET_CPUID2) that is consistent with
+hardware, kernel, and userspace capabilities, and with user requirements (for
+example, the user may wish to constrain cpuid to emulate older hardware,
+or for feature consistency across a cluster).
+
+Userspace invokes KVM_GET_SUPPORTED_CPUID by passing a kvm_cpuid2 structure
+with the 'nent' field indicating the number of entries in the variable-size
+array 'entries'. If the number of entries is too low to describe the cpu
+capabilities, an error (E2BIG) is returned. If the number is too high,
+the 'nent' field is adjusted and an error (ENOMEM) is returned. If the
+number is just right, the 'nent' field is adjusted to the number of valid
+entries in the 'entries' array, which is then filled.
+
+The entries returned are the host cpuid as returned by the cpuid instruction,
+with unknown or unsupported features masked out. Some features (for example,
+x2apic), may not be present in the host cpu, but are exposed by kvm if it can
+emulate them efficiently. The fields in each entry are defined as follows:
+
+ function: the eax value used to obtain the entry
+ index: the ecx value used to obtain the entry (for entries that are
+ affected by ecx)
+ flags: an OR of zero or more of the following:
+ KVM_CPUID_FLAG_SIGNIFCANT_INDEX:
+ if the index field is valid
+ KVM_CPUID_FLAG_STATEFUL_FUNC:
+ if cpuid for this function returns different values for successive
+ invocations; there will be several entries with the same function,
+ all with this flag set
+ KVM_CPUID_FLAG_STATE_READ_NEXT:
+ for KVM_CPUID_FLAG_STATEFUL_FUNC entries, set if this entry is
+ the first entry to be read by a cpu
+ eax, ebx, ecx, edx: the values returned by the cpuid instruction for
+ this function/index combination
+
+The TSC deadline timer feature (CPUID leaf 1, ecx[24]) is always returned
+as false, since the feature depends on KVM_CREATE_IRQCHIP for local APIC
+support. Instead it is reported via
+
+ ioctl(KVM_CHECK_EXTENSION, KVM_CAP_TSC_DEADLINE_TIMER)
+
+if that returns true and you use KVM_CREATE_IRQCHIP, or if you emulate the
+feature in userspace, then you can enable the feature for KVM_SET_CPUID2.
+
+4.47 KVM_PPC_GET_PVINFO
+
+Capability: KVM_CAP_PPC_GET_PVINFO
+Architectures: ppc
+Type: vm ioctl
+Parameters: struct kvm_ppc_pvinfo (out)
+Returns: 0 on success, !0 on error
+
+struct kvm_ppc_pvinfo {
+ __u32 flags;
+ __u32 hcall[4];
+ __u8 pad[108];
+};
+
+This ioctl fetches PV specific information that need to be passed to the guest
+using the device tree or other means from vm context.
+
+For now the only implemented piece of information distributed here is an array
+of 4 instructions that make up a hypercall.
+
+If any additional field gets added to this structure later on, a bit for that
+additional piece of information will be set in the flags bitmap.
+
+4.48 KVM_ASSIGN_PCI_DEVICE
+
+Capability: KVM_CAP_DEVICE_ASSIGNMENT
+Architectures: x86 ia64
+Type: vm ioctl
+Parameters: struct kvm_assigned_pci_dev (in)
+Returns: 0 on success, -1 on error
+
+Assigns a host PCI device to the VM.
+
+struct kvm_assigned_pci_dev {
+ __u32 assigned_dev_id;
+ __u32 busnr;
+ __u32 devfn;
+ __u32 flags;
+ __u32 segnr;
+ union {
+ __u32 reserved[11];
+ };
+};
+
+The PCI device is specified by the triple segnr, busnr, and devfn.
+Identification in succeeding service requests is done via assigned_dev_id. The
+following flags are specified:
+
+/* Depends on KVM_CAP_IOMMU */
+#define KVM_DEV_ASSIGN_ENABLE_IOMMU (1 << 0)
+
+The KVM_DEV_ASSIGN_ENABLE_IOMMU flag is a mandatory option to ensure
+isolation of the device. Usages not specifying this flag are deprecated.
+
+Only PCI header type 0 devices with PCI BAR resources are supported by
+device assignment. The user requesting this ioctl must have read/write
+access to the PCI sysfs resource files associated with the device.
+
+4.49 KVM_DEASSIGN_PCI_DEVICE
+
+Capability: KVM_CAP_DEVICE_DEASSIGNMENT
+Architectures: x86 ia64
+Type: vm ioctl
+Parameters: struct kvm_assigned_pci_dev (in)
+Returns: 0 on success, -1 on error
+
+Ends PCI device assignment, releasing all associated resources.
+
+See KVM_CAP_DEVICE_ASSIGNMENT for the data structure. Only assigned_dev_id is
+used in kvm_assigned_pci_dev to identify the device.
+
+4.50 KVM_ASSIGN_DEV_IRQ
+
+Capability: KVM_CAP_ASSIGN_DEV_IRQ
+Architectures: x86 ia64
+Type: vm ioctl
+Parameters: struct kvm_assigned_irq (in)
+Returns: 0 on success, -1 on error
+
+Assigns an IRQ to a passed-through device.
+
+struct kvm_assigned_irq {
+ __u32 assigned_dev_id;
+ __u32 host_irq; /* ignored (legacy field) */
+ __u32 guest_irq;
+ __u32 flags;
+ union {
+ __u32 reserved[12];
+ };
+};
+
+The following flags are defined:
+
+#define KVM_DEV_IRQ_HOST_INTX (1 << 0)
+#define KVM_DEV_IRQ_HOST_MSI (1 << 1)
+#define KVM_DEV_IRQ_HOST_MSIX (1 << 2)
+
+#define KVM_DEV_IRQ_GUEST_INTX (1 << 8)
+#define KVM_DEV_IRQ_GUEST_MSI (1 << 9)
+#define KVM_DEV_IRQ_GUEST_MSIX (1 << 10)
+
+It is not valid to specify multiple types per host or guest IRQ. However, the
+IRQ type of host and guest can differ or can even be null.
+
+4.51 KVM_DEASSIGN_DEV_IRQ
+
+Capability: KVM_CAP_ASSIGN_DEV_IRQ
+Architectures: x86 ia64
+Type: vm ioctl
+Parameters: struct kvm_assigned_irq (in)
+Returns: 0 on success, -1 on error
+
+Ends an IRQ assignment to a passed-through device.
+
+See KVM_ASSIGN_DEV_IRQ for the data structure. The target device is specified
+by assigned_dev_id, flags must correspond to the IRQ type specified on
+KVM_ASSIGN_DEV_IRQ. Partial deassignment of host or guest IRQ is allowed.
+
+4.52 KVM_SET_GSI_ROUTING
+
+Capability: KVM_CAP_IRQ_ROUTING
+Architectures: x86 ia64
+Type: vm ioctl
+Parameters: struct kvm_irq_routing (in)
+Returns: 0 on success, -1 on error
+
+Sets the GSI routing table entries, overwriting any previously set entries.
+
+struct kvm_irq_routing {
+ __u32 nr;
+ __u32 flags;
+ struct kvm_irq_routing_entry entries[0];
+};
+
+No flags are specified so far, the corresponding field must be set to zero.
+
+struct kvm_irq_routing_entry {
+ __u32 gsi;
+ __u32 type;
+ __u32 flags;
+ __u32 pad;
+ union {
+ struct kvm_irq_routing_irqchip irqchip;
+ struct kvm_irq_routing_msi msi;
+ __u32 pad[8];
+ } u;
+};
+
+/* gsi routing entry types */
+#define KVM_IRQ_ROUTING_IRQCHIP 1
+#define KVM_IRQ_ROUTING_MSI 2
+
+No flags are specified so far, the corresponding field must be set to zero.
+
+struct kvm_irq_routing_irqchip {
+ __u32 irqchip;
+ __u32 pin;
+};
+
+struct kvm_irq_routing_msi {
+ __u32 address_lo;
+ __u32 address_hi;
+ __u32 data;
+ __u32 pad;
+};
+
+4.53 KVM_ASSIGN_SET_MSIX_NR
+
+Capability: KVM_CAP_DEVICE_MSIX
+Architectures: x86 ia64
+Type: vm ioctl
+Parameters: struct kvm_assigned_msix_nr (in)
+Returns: 0 on success, -1 on error
+
+Set the number of MSI-X interrupts for an assigned device. The number is
+reset again by terminating the MSI-X assignment of the device via
+KVM_DEASSIGN_DEV_IRQ. Calling this service more than once at any earlier
+point will fail.
+
+struct kvm_assigned_msix_nr {
+ __u32 assigned_dev_id;
+ __u16 entry_nr;
+ __u16 padding;
+};
+
+#define KVM_MAX_MSIX_PER_DEV 256
+
+4.54 KVM_ASSIGN_SET_MSIX_ENTRY
+
+Capability: KVM_CAP_DEVICE_MSIX
+Architectures: x86 ia64
+Type: vm ioctl
+Parameters: struct kvm_assigned_msix_entry (in)
+Returns: 0 on success, -1 on error
+
+Specifies the routing of an MSI-X assigned device interrupt to a GSI. Setting
+the GSI vector to zero means disabling the interrupt.
+
+struct kvm_assigned_msix_entry {
+ __u32 assigned_dev_id;
+ __u32 gsi;
+ __u16 entry; /* The index of entry in the MSI-X table */
+ __u16 padding[3];
+};
+
+4.54 KVM_SET_TSC_KHZ
+
+Capability: KVM_CAP_TSC_CONTROL
+Architectures: x86
+Type: vcpu ioctl
+Parameters: virtual tsc_khz
+Returns: 0 on success, -1 on error
+
+Specifies the tsc frequency for the virtual machine. The unit of the
+frequency is KHz.
+
+4.55 KVM_GET_TSC_KHZ
+
+Capability: KVM_CAP_GET_TSC_KHZ
+Architectures: x86
+Type: vcpu ioctl
+Parameters: none
+Returns: virtual tsc-khz on success, negative value on error
+
+Returns the tsc frequency of the guest. The unit of the return value is
+KHz. If the host has unstable tsc this ioctl returns -EIO instead as an
+error.
+
+4.56 KVM_GET_LAPIC
+
+Capability: KVM_CAP_IRQCHIP
+Architectures: x86
+Type: vcpu ioctl
+Parameters: struct kvm_lapic_state (out)
+Returns: 0 on success, -1 on error
+
+#define KVM_APIC_REG_SIZE 0x400
+struct kvm_lapic_state {
+ char regs[KVM_APIC_REG_SIZE];
+};
+
+Reads the Local APIC registers and copies them into the input argument. The
+data format and layout are the same as documented in the architecture manual.
+
+4.57 KVM_SET_LAPIC
+
+Capability: KVM_CAP_IRQCHIP
+Architectures: x86
+Type: vcpu ioctl
+Parameters: struct kvm_lapic_state (in)
+Returns: 0 on success, -1 on error
+
+#define KVM_APIC_REG_SIZE 0x400
+struct kvm_lapic_state {
+ char regs[KVM_APIC_REG_SIZE];
+};
+
+Copies the input argument into the the Local APIC registers. The data format
+and layout are the same as documented in the architecture manual.
+
+4.58 KVM_IOEVENTFD
+
+Capability: KVM_CAP_IOEVENTFD
+Architectures: all
+Type: vm ioctl
+Parameters: struct kvm_ioeventfd (in)
+Returns: 0 on success, !0 on error
+
+This ioctl attaches or detaches an ioeventfd to a legal pio/mmio address
+within the guest. A guest write in the registered address will signal the
+provided event instead of triggering an exit.
+
+struct kvm_ioeventfd {
+ __u64 datamatch;
+ __u64 addr; /* legal pio/mmio address */
+ __u32 len; /* 1, 2, 4, or 8 bytes */
+ __s32 fd;
+ __u32 flags;
+ __u8 pad[36];
+};
+
+The following flags are defined:
+
+#define KVM_IOEVENTFD_FLAG_DATAMATCH (1 << kvm_ioeventfd_flag_nr_datamatch)
+#define KVM_IOEVENTFD_FLAG_PIO (1 << kvm_ioeventfd_flag_nr_pio)
+#define KVM_IOEVENTFD_FLAG_DEASSIGN (1 << kvm_ioeventfd_flag_nr_deassign)
+
+If datamatch flag is set, the event will be signaled only if the written value
+to the registered address is equal to datamatch in struct kvm_ioeventfd.
+
+4.62 KVM_CREATE_SPAPR_TCE
+
+Capability: KVM_CAP_SPAPR_TCE
+Architectures: powerpc
+Type: vm ioctl
+Parameters: struct kvm_create_spapr_tce (in)
+Returns: file descriptor for manipulating the created TCE table
+
+This creates a virtual TCE (translation control entry) table, which
+is an IOMMU for PAPR-style virtual I/O. It is used to translate
+logical addresses used in virtual I/O into guest physical addresses,
+and provides a scatter/gather capability for PAPR virtual I/O.
+
+/* for KVM_CAP_SPAPR_TCE */
+struct kvm_create_spapr_tce {
+ __u64 liobn;
+ __u32 window_size;
+};
+
+The liobn field gives the logical IO bus number for which to create a
+TCE table. The window_size field specifies the size of the DMA window
+which this TCE table will translate - the table will contain one 64
+bit TCE entry for every 4kiB of the DMA window.
+
+When the guest issues an H_PUT_TCE hcall on a liobn for which a TCE
+table has been created using this ioctl(), the kernel will handle it
+in real mode, updating the TCE table. H_PUT_TCE calls for other
+liobns will cause a vm exit and must be handled by userspace.
+
+The return value is a file descriptor which can be passed to mmap(2)
+to map the created TCE table into userspace. This lets userspace read
+the entries written by kernel-handled H_PUT_TCE calls, and also lets
+userspace update the TCE table directly which is useful in some
+circumstances.
+
+4.63 KVM_ALLOCATE_RMA
+
+Capability: KVM_CAP_PPC_RMA
+Architectures: powerpc
+Type: vm ioctl
+Parameters: struct kvm_allocate_rma (out)
+Returns: file descriptor for mapping the allocated RMA
+
+This allocates a Real Mode Area (RMA) from the pool allocated at boot
+time by the kernel. An RMA is a physically-contiguous, aligned region
+of memory used on older POWER processors to provide the memory which
+will be accessed by real-mode (MMU off) accesses in a KVM guest.
+POWER processors support a set of sizes for the RMA that usually
+includes 64MB, 128MB, 256MB and some larger powers of two.
+
+/* for KVM_ALLOCATE_RMA */
+struct kvm_allocate_rma {
+ __u64 rma_size;
+};
+
+The return value is a file descriptor which can be passed to mmap(2)
+to map the allocated RMA into userspace. The mapped area can then be
+passed to the KVM_SET_USER_MEMORY_REGION ioctl to establish it as the
+RMA for a virtual machine. The size of the RMA in bytes (which is
+fixed at host kernel boot time) is returned in the rma_size field of
+the argument structure.
+
+The KVM_CAP_PPC_RMA capability is 1 or 2 if the KVM_ALLOCATE_RMA ioctl
+is supported; 2 if the processor requires all virtual machines to have
+an RMA, or 1 if the processor can use an RMA but doesn't require it,
+because it supports the Virtual RMA (VRMA) facility.
+
+4.64 KVM_NMI
+
+Capability: KVM_CAP_USER_NMI
+Architectures: x86
+Type: vcpu ioctl
+Parameters: none
+Returns: 0 on success, -1 on error
+
+Queues an NMI on the thread's vcpu. Note this is well defined only
+when KVM_CREATE_IRQCHIP has not been called, since this is an interface
+between the virtual cpu core and virtual local APIC. After KVM_CREATE_IRQCHIP
+has been called, this interface is completely emulated within the kernel.
+
+To use this to emulate the LINT1 input with KVM_CREATE_IRQCHIP, use the
+following algorithm:
+
+ - pause the vpcu
+ - read the local APIC's state (KVM_GET_LAPIC)
+ - check whether changing LINT1 will queue an NMI (see the LVT entry for LINT1)
+ - if so, issue KVM_NMI
+ - resume the vcpu
+
+Some guests configure the LINT1 NMI input to cause a panic, aiding in
+debugging.
+
+5. The kvm_run structure
+
+Application code obtains a pointer to the kvm_run structure by
+mmap()ing a vcpu fd. From that point, application code can control
+execution by changing fields in kvm_run prior to calling the KVM_RUN
+ioctl, and obtain information about the reason KVM_RUN returned by
+looking up structure members.
+
+struct kvm_run {
+ /* in */
+ __u8 request_interrupt_window;
+
+Request that KVM_RUN return when it becomes possible to inject external
+interrupts into the guest. Useful in conjunction with KVM_INTERRUPT.
+
+ __u8 padding1[7];
+
+ /* out */
+ __u32 exit_reason;
+
+When KVM_RUN has returned successfully (return value 0), this informs
+application code why KVM_RUN has returned. Allowable values for this
+field are detailed below.
+
+ __u8 ready_for_interrupt_injection;
+
+If request_interrupt_window has been specified, this field indicates
+an interrupt can be injected now with KVM_INTERRUPT.
+
+ __u8 if_flag;
+
+The value of the current interrupt flag. Only valid if in-kernel
+local APIC is not used.
+
+ __u8 padding2[2];
+
+ /* in (pre_kvm_run), out (post_kvm_run) */
+ __u64 cr8;
+
+The value of the cr8 register. Only valid if in-kernel local APIC is
+not used. Both input and output.
+
+ __u64 apic_base;
+
+The value of the APIC BASE msr. Only valid if in-kernel local
+APIC is not used. Both input and output.
+
+ union {
+ /* KVM_EXIT_UNKNOWN */
+ struct {
+ __u64 hardware_exit_reason;
+ } hw;
+
+If exit_reason is KVM_EXIT_UNKNOWN, the vcpu has exited due to unknown
+reasons. Further architecture-specific information is available in
+hardware_exit_reason.
+
+ /* KVM_EXIT_FAIL_ENTRY */
+ struct {
+ __u64 hardware_entry_failure_reason;
+ } fail_entry;
+
+If exit_reason is KVM_EXIT_FAIL_ENTRY, the vcpu could not be run due
+to unknown reasons. Further architecture-specific information is
+available in hardware_entry_failure_reason.
+
+ /* KVM_EXIT_EXCEPTION */
+ struct {
+ __u32 exception;
+ __u32 error_code;
+ } ex;
+
+Unused.
+
+ /* KVM_EXIT_IO */
+ struct {
+#define KVM_EXIT_IO_IN 0
+#define KVM_EXIT_IO_OUT 1
+ __u8 direction;
+ __u8 size; /* bytes */
+ __u16 port;
+ __u32 count;
+ __u64 data_offset; /* relative to kvm_run start */
+ } io;
+
+If exit_reason is KVM_EXIT_IO, then the vcpu has
+executed a port I/O instruction which could not be satisfied by kvm.
+data_offset describes where the data is located (KVM_EXIT_IO_OUT) or
+where kvm expects application code to place the data for the next
+KVM_RUN invocation (KVM_EXIT_IO_IN). Data format is a packed array.
+
+ struct {
+ struct kvm_debug_exit_arch arch;
+ } debug;
+
+Unused.
+
+ /* KVM_EXIT_MMIO */
+ struct {
+ __u64 phys_addr;
+ __u8 data[8];
+ __u32 len;
+ __u8 is_write;
+ } mmio;
+
+If exit_reason is KVM_EXIT_MMIO, then the vcpu has
+executed a memory-mapped I/O instruction which could not be satisfied
+by kvm. The 'data' member contains the written data if 'is_write' is
+true, and should be filled by application code otherwise.
+
+NOTE: For KVM_EXIT_IO, KVM_EXIT_MMIO and KVM_EXIT_OSI, the corresponding
+operations are complete (and guest state is consistent) only after userspace
+has re-entered the kernel with KVM_RUN. The kernel side will first finish
+incomplete operations and then check for pending signals. Userspace
+can re-enter the guest with an unmasked signal pending to complete
+pending operations.
+
+ /* KVM_EXIT_HYPERCALL */
+ struct {
+ __u64 nr;
+ __u64 args[6];
+ __u64 ret;
+ __u32 longmode;
+ __u32 pad;
+ } hypercall;
+
+Unused. This was once used for 'hypercall to userspace'. To implement
+such functionality, use KVM_EXIT_IO (x86) or KVM_EXIT_MMIO (all except s390).
+Note KVM_EXIT_IO is significantly faster than KVM_EXIT_MMIO.
+
+ /* KVM_EXIT_TPR_ACCESS */
+ struct {
+ __u64 rip;
+ __u32 is_write;
+ __u32 pad;
+ } tpr_access;
+
+To be documented (KVM_TPR_ACCESS_REPORTING).
+
+ /* KVM_EXIT_S390_SIEIC */
+ struct {
+ __u8 icptcode;
+ __u64 mask; /* psw upper half */
+ __u64 addr; /* psw lower half */
+ __u16 ipa;
+ __u32 ipb;
+ } s390_sieic;
+
+s390 specific.
+
+ /* KVM_EXIT_S390_RESET */
+#define KVM_S390_RESET_POR 1
+#define KVM_S390_RESET_CLEAR 2
+#define KVM_S390_RESET_SUBSYSTEM 4
+#define KVM_S390_RESET_CPU_INIT 8
+#define KVM_S390_RESET_IPL 16
+ __u64 s390_reset_flags;
+
+s390 specific.
+
+ /* KVM_EXIT_DCR */
+ struct {
+ __u32 dcrn;
+ __u32 data;
+ __u8 is_write;
+ } dcr;
+
+powerpc specific.
+
+ /* KVM_EXIT_OSI */
+ struct {
+ __u64 gprs[32];
+ } osi;
+
+MOL uses a special hypercall interface it calls 'OSI'. To enable it, we catch
+hypercalls and exit with this exit struct that contains all the guest gprs.
+
+If exit_reason is KVM_EXIT_OSI, then the vcpu has triggered such a hypercall.
+Userspace can now handle the hypercall and when it's done modify the gprs as
+necessary. Upon guest entry all guest GPRs will then be replaced by the values
+in this struct.
+
+ /* KVM_EXIT_PAPR_HCALL */
+ struct {
+ __u64 nr;
+ __u64 ret;
+ __u64 args[9];
+ } papr_hcall;
+
+This is used on 64-bit PowerPC when emulating a pSeries partition,
+e.g. with the 'pseries' machine type in qemu. It occurs when the
+guest does a hypercall using the 'sc 1' instruction. The 'nr' field
+contains the hypercall number (from the guest R3), and 'args' contains
+the arguments (from the guest R4 - R12). Userspace should put the
+return code in 'ret' and any extra returned values in args[].
+The possible hypercalls are defined in the Power Architecture Platform
+Requirements (PAPR) document available from www.power.org (free
+developer registration required to access it).
+
+ /* Fix the size of the union. */
+ char padding[256];
+ };
+};
+
+6. Capabilities that can be enabled
+
+There are certain capabilities that change the behavior of the virtual CPU when
+enabled. To enable them, please see section 4.37. Below you can find a list of
+capabilities and what their effect on the vCPU is when enabling them.
+
+The following information is provided along with the description:
+
+ Architectures: which instruction set architectures provide this ioctl.
+ x86 includes both i386 and x86_64.
+
+ Parameters: what parameters are accepted by the capability.
+
+ Returns: the return value. General error numbers (EBADF, ENOMEM, EINVAL)
+ are not detailed, but errors with specific meanings are.
+
+6.1 KVM_CAP_PPC_OSI
+
+Architectures: ppc
+Parameters: none
+Returns: 0 on success; -1 on error
+
+This capability enables interception of OSI hypercalls that otherwise would
+be treated as normal system calls to be injected into the guest. OSI hypercalls
+were invented by Mac-on-Linux to have a standardized communication mechanism
+between the guest and the host.
+
+When this capability is enabled, KVM_EXIT_OSI can occur.
+
+6.2 KVM_CAP_PPC_PAPR
+
+Architectures: ppc
+Parameters: none
+Returns: 0 on success; -1 on error
+
+This capability enables interception of PAPR hypercalls. PAPR hypercalls are
+done using the hypercall instruction "sc 1".
+
+It also sets the guest privilege level to "supervisor" mode. Usually the guest
+runs in "hypervisor" privilege mode with a few missing features.
+
+In addition to the above, it changes the semantics of SDR1. In this mode, the
+HTAB address part of SDR1 contains an HVA instead of a GPA, as PAPR keeps the
+HTAB invisible to the guest.
+
+When this capability is enabled, KVM_EXIT_PAPR_HCALL can occur.
diff --git a/Documentation/virtual/kvm/cpuid.txt b/Documentation/virtual/kvm/cpuid.txt
new file mode 100644
index 00000000000..882068538c9
--- /dev/null
+++ b/Documentation/virtual/kvm/cpuid.txt
@@ -0,0 +1,45 @@
+KVM CPUID bits
+Glauber Costa <glommer@redhat.com>, Red Hat Inc, 2010
+=====================================================
+
+A guest running on a kvm host, can check some of its features using
+cpuid. This is not always guaranteed to work, since userspace can
+mask-out some, or even all KVM-related cpuid features before launching
+a guest.
+
+KVM cpuid functions are:
+
+function: KVM_CPUID_SIGNATURE (0x40000000)
+returns : eax = 0,
+ ebx = 0x4b4d564b,
+ ecx = 0x564b4d56,
+ edx = 0x4d.
+Note that this value in ebx, ecx and edx corresponds to the string "KVMKVMKVM".
+This function queries the presence of KVM cpuid leafs.
+
+
+function: define KVM_CPUID_FEATURES (0x40000001)
+returns : ebx, ecx, edx = 0
+ eax = and OR'ed group of (1 << flag), where each flags is:
+
+
+flag || value || meaning
+=============================================================================
+KVM_FEATURE_CLOCKSOURCE || 0 || kvmclock available at msrs
+ || || 0x11 and 0x12.
+------------------------------------------------------------------------------
+KVM_FEATURE_NOP_IO_DELAY || 1 || not necessary to perform delays
+ || || on PIO operations.
+------------------------------------------------------------------------------
+KVM_FEATURE_MMU_OP || 2 || deprecated.
+------------------------------------------------------------------------------
+KVM_FEATURE_CLOCKSOURCE2 || 3 || kvmclock available at msrs
+ || || 0x4b564d00 and 0x4b564d01
+------------------------------------------------------------------------------
+KVM_FEATURE_ASYNC_PF || 4 || async pf can be enabled by
+ || || writing to msr 0x4b564d02
+------------------------------------------------------------------------------
+KVM_FEATURE_CLOCKSOURCE_STABLE_BIT || 24 || host will warn if no guest-side
+ || || per-cpu warps are expected in
+ || || kvmclock.
+------------------------------------------------------------------------------
diff --git a/Documentation/virtual/kvm/locking.txt b/Documentation/virtual/kvm/locking.txt
new file mode 100644
index 00000000000..3b4cd3bf563
--- /dev/null
+++ b/Documentation/virtual/kvm/locking.txt
@@ -0,0 +1,25 @@
+KVM Lock Overview
+=================
+
+1. Acquisition Orders
+---------------------
+
+(to be written)
+
+2. Reference
+------------
+
+Name: kvm_lock
+Type: raw_spinlock
+Arch: any
+Protects: - vm_list
+ - hardware virtualization enable/disable
+Comment: 'raw' because hardware enabling/disabling must be atomic /wrt
+ migration.
+
+Name: kvm_arch::tsc_write_lock
+Type: raw_spinlock
+Arch: x86
+Protects: - kvm_arch::{last_tsc_write,last_tsc_nsec,last_tsc_offset}
+ - tsc offset in vmcb
+Comment: 'raw' because updating the tsc offsets must not be preempted.
diff --git a/Documentation/virtual/kvm/mmu.txt b/Documentation/virtual/kvm/mmu.txt
new file mode 100644
index 00000000000..5dc972c09b5
--- /dev/null
+++ b/Documentation/virtual/kvm/mmu.txt
@@ -0,0 +1,366 @@
+The x86 kvm shadow mmu
+======================
+
+The mmu (in arch/x86/kvm, files mmu.[ch] and paging_tmpl.h) is responsible
+for presenting a standard x86 mmu to the guest, while translating guest
+physical addresses to host physical addresses.
+
+The mmu code attempts to satisfy the following requirements:
+
+- correctness: the guest should not be able to determine that it is running
+ on an emulated mmu except for timing (we attempt to comply
+ with the specification, not emulate the characteristics of
+ a particular implementation such as tlb size)
+- security: the guest must not be able to touch host memory not assigned
+ to it
+- performance: minimize the performance penalty imposed by the mmu
+- scaling: need to scale to large memory and large vcpu guests
+- hardware: support the full range of x86 virtualization hardware
+- integration: Linux memory management code must be in control of guest memory
+ so that swapping, page migration, page merging, transparent
+ hugepages, and similar features work without change
+- dirty tracking: report writes to guest memory to enable live migration
+ and framebuffer-based displays
+- footprint: keep the amount of pinned kernel memory low (most memory
+ should be shrinkable)
+- reliability: avoid multipage or GFP_ATOMIC allocations
+
+Acronyms
+========
+
+pfn host page frame number
+hpa host physical address
+hva host virtual address
+gfn guest frame number
+gpa guest physical address
+gva guest virtual address
+ngpa nested guest physical address
+ngva nested guest virtual address
+pte page table entry (used also to refer generically to paging structure
+ entries)
+gpte guest pte (referring to gfns)
+spte shadow pte (referring to pfns)
+tdp two dimensional paging (vendor neutral term for NPT and EPT)
+
+Virtual and real hardware supported
+===================================
+
+The mmu supports first-generation mmu hardware, which allows an atomic switch
+of the current paging mode and cr3 during guest entry, as well as
+two-dimensional paging (AMD's NPT and Intel's EPT). The emulated hardware
+it exposes is the traditional 2/3/4 level x86 mmu, with support for global
+pages, pae, pse, pse36, cr0.wp, and 1GB pages. Work is in progress to support
+exposing NPT capable hardware on NPT capable hosts.
+
+Translation
+===========
+
+The primary job of the mmu is to program the processor's mmu to translate
+addresses for the guest. Different translations are required at different
+times:
+
+- when guest paging is disabled, we translate guest physical addresses to
+ host physical addresses (gpa->hpa)
+- when guest paging is enabled, we translate guest virtual addresses, to
+ guest physical addresses, to host physical addresses (gva->gpa->hpa)
+- when the guest launches a guest of its own, we translate nested guest
+ virtual addresses, to nested guest physical addresses, to guest physical
+ addresses, to host physical addresses (ngva->ngpa->gpa->hpa)
+
+The primary challenge is to encode between 1 and 3 translations into hardware
+that support only 1 (traditional) and 2 (tdp) translations. When the
+number of required translations matches the hardware, the mmu operates in
+direct mode; otherwise it operates in shadow mode (see below).
+
+Memory
+======
+
+Guest memory (gpa) is part of the user address space of the process that is
+using kvm. Userspace defines the translation between guest addresses and user
+addresses (gpa->hva); note that two gpas may alias to the same hva, but not
+vice versa.
+
+These hvas may be backed using any method available to the host: anonymous
+memory, file backed memory, and device memory. Memory might be paged by the
+host at any time.
+
+Events
+======
+
+The mmu is driven by events, some from the guest, some from the host.
+
+Guest generated events:
+- writes to control registers (especially cr3)
+- invlpg/invlpga instruction execution
+- access to missing or protected translations
+
+Host generated events:
+- changes in the gpa->hpa translation (either through gpa->hva changes or
+ through hva->hpa changes)
+- memory pressure (the shrinker)
+
+Shadow pages
+============
+
+The principal data structure is the shadow page, 'struct kvm_mmu_page'. A
+shadow page contains 512 sptes, which can be either leaf or nonleaf sptes. A
+shadow page may contain a mix of leaf and nonleaf sptes.
+
+A nonleaf spte allows the hardware mmu to reach the leaf pages and
+is not related to a translation directly. It points to other shadow pages.
+
+A leaf spte corresponds to either one or two translations encoded into
+one paging structure entry. These are always the lowest level of the
+translation stack, with optional higher level translations left to NPT/EPT.
+Leaf ptes point at guest pages.
+
+The following table shows translations encoded by leaf ptes, with higher-level
+translations in parentheses:
+
+ Non-nested guests:
+ nonpaging: gpa->hpa
+ paging: gva->gpa->hpa
+ paging, tdp: (gva->)gpa->hpa
+ Nested guests:
+ non-tdp: ngva->gpa->hpa (*)
+ tdp: (ngva->)ngpa->gpa->hpa
+
+(*) the guest hypervisor will encode the ngva->gpa translation into its page
+ tables if npt is not present
+
+Shadow pages contain the following information:
+ role.level:
+ The level in the shadow paging hierarchy that this shadow page belongs to.
+ 1=4k sptes, 2=2M sptes, 3=1G sptes, etc.
+ role.direct:
+ If set, leaf sptes reachable from this page are for a linear range.
+ Examples include real mode translation, large guest pages backed by small
+ host pages, and gpa->hpa translations when NPT or EPT is active.
+ The linear range starts at (gfn << PAGE_SHIFT) and its size is determined
+ by role.level (2MB for first level, 1GB for second level, 0.5TB for third
+ level, 256TB for fourth level)
+ If clear, this page corresponds to a guest page table denoted by the gfn
+ field.
+ role.quadrant:
+ When role.cr4_pae=0, the guest uses 32-bit gptes while the host uses 64-bit
+ sptes. That means a guest page table contains more ptes than the host,
+ so multiple shadow pages are needed to shadow one guest page.
+ For first-level shadow pages, role.quadrant can be 0 or 1 and denotes the
+ first or second 512-gpte block in the guest page table. For second-level
+ page tables, each 32-bit gpte is converted to two 64-bit sptes
+ (since each first-level guest page is shadowed by two first-level
+ shadow pages) so role.quadrant takes values in the range 0..3. Each
+ quadrant maps 1GB virtual address space.
+ role.access:
+ Inherited guest access permissions in the form uwx. Note execute
+ permission is positive, not negative.
+ role.invalid:
+ The page is invalid and should not be used. It is a root page that is
+ currently pinned (by a cpu hardware register pointing to it); once it is
+ unpinned it will be destroyed.
+ role.cr4_pae:
+ Contains the value of cr4.pae for which the page is valid (e.g. whether
+ 32-bit or 64-bit gptes are in use).
+ role.nxe:
+ Contains the value of efer.nxe for which the page is valid.
+ role.cr0_wp:
+ Contains the value of cr0.wp for which the page is valid.
+ role.smep_andnot_wp:
+ Contains the value of cr4.smep && !cr0.wp for which the page is valid
+ (pages for which this is true are different from other pages; see the
+ treatment of cr0.wp=0 below).
+ gfn:
+ Either the guest page table containing the translations shadowed by this
+ page, or the base page frame for linear translations. See role.direct.
+ spt:
+ A pageful of 64-bit sptes containing the translations for this page.
+ Accessed by both kvm and hardware.
+ The page pointed to by spt will have its page->private pointing back
+ at the shadow page structure.
+ sptes in spt point either at guest pages, or at lower-level shadow pages.
+ Specifically, if sp1 and sp2 are shadow pages, then sp1->spt[n] may point
+ at __pa(sp2->spt). sp2 will point back at sp1 through parent_pte.
+ The spt array forms a DAG structure with the shadow page as a node, and
+ guest pages as leaves.
+ gfns:
+ An array of 512 guest frame numbers, one for each present pte. Used to
+ perform a reverse map from a pte to a gfn. When role.direct is set, any
+ element of this array can be calculated from the gfn field when used, in
+ this case, the array of gfns is not allocated. See role.direct and gfn.
+ slot_bitmap:
+ A bitmap containing one bit per memory slot. If the page contains a pte
+ mapping a page from memory slot n, then bit n of slot_bitmap will be set
+ (if a page is aliased among several slots, then it is not guaranteed that
+ all slots will be marked).
+ Used during dirty logging to avoid scanning a shadow page if none if its
+ pages need tracking.
+ root_count:
+ A counter keeping track of how many hardware registers (guest cr3 or
+ pdptrs) are now pointing at the page. While this counter is nonzero, the
+ page cannot be destroyed. See role.invalid.
+ multimapped:
+ Whether there exist multiple sptes pointing at this page.
+ parent_pte/parent_ptes:
+ If multimapped is zero, parent_pte points at the single spte that points at
+ this page's spt. Otherwise, parent_ptes points at a data structure
+ with a list of parent_ptes.
+ unsync:
+ If true, then the translations in this page may not match the guest's
+ translation. This is equivalent to the state of the tlb when a pte is
+ changed but before the tlb entry is flushed. Accordingly, unsync ptes
+ are synchronized when the guest executes invlpg or flushes its tlb by
+ other means. Valid for leaf pages.
+ unsync_children:
+ How many sptes in the page point at pages that are unsync (or have
+ unsynchronized children).
+ unsync_child_bitmap:
+ A bitmap indicating which sptes in spt point (directly or indirectly) at
+ pages that may be unsynchronized. Used to quickly locate all unsychronized
+ pages reachable from a given page.
+
+Reverse map
+===========
+
+The mmu maintains a reverse mapping whereby all ptes mapping a page can be
+reached given its gfn. This is used, for example, when swapping out a page.
+
+Synchronized and unsynchronized pages
+=====================================
+
+The guest uses two events to synchronize its tlb and page tables: tlb flushes
+and page invalidations (invlpg).
+
+A tlb flush means that we need to synchronize all sptes reachable from the
+guest's cr3. This is expensive, so we keep all guest page tables write
+protected, and synchronize sptes to gptes when a gpte is written.
+
+A special case is when a guest page table is reachable from the current
+guest cr3. In this case, the guest is obliged to issue an invlpg instruction
+before using the translation. We take advantage of that by removing write
+protection from the guest page, and allowing the guest to modify it freely.
+We synchronize modified gptes when the guest invokes invlpg. This reduces
+the amount of emulation we have to do when the guest modifies multiple gptes,
+or when the a guest page is no longer used as a page table and is used for
+random guest data.
+
+As a side effect we have to resynchronize all reachable unsynchronized shadow
+pages on a tlb flush.
+
+
+Reaction to events
+==================
+
+- guest page fault (or npt page fault, or ept violation)
+
+This is the most complicated event. The cause of a page fault can be:
+
+ - a true guest fault (the guest translation won't allow the access) (*)
+ - access to a missing translation
+ - access to a protected translation
+ - when logging dirty pages, memory is write protected
+ - synchronized shadow pages are write protected (*)
+ - access to untranslatable memory (mmio)
+
+ (*) not applicable in direct mode
+
+Handling a page fault is performed as follows:
+
+ - if needed, walk the guest page tables to determine the guest translation
+ (gva->gpa or ngpa->gpa)
+ - if permissions are insufficient, reflect the fault back to the guest
+ - determine the host page
+ - if this is an mmio request, there is no host page; call the emulator
+ to emulate the instruction instead
+ - walk the shadow page table to find the spte for the translation,
+ instantiating missing intermediate page tables as necessary
+ - try to unsynchronize the page
+ - if successful, we can let the guest continue and modify the gpte
+ - emulate the instruction
+ - if failed, unshadow the page and let the guest continue
+ - update any translations that were modified by the instruction
+
+invlpg handling:
+
+ - walk the shadow page hierarchy and drop affected translations
+ - try to reinstantiate the indicated translation in the hope that the
+ guest will use it in the near future
+
+Guest control register updates:
+
+- mov to cr3
+ - look up new shadow roots
+ - synchronize newly reachable shadow pages
+
+- mov to cr0/cr4/efer
+ - set up mmu context for new paging mode
+ - look up new shadow roots
+ - synchronize newly reachable shadow pages
+
+Host translation updates:
+
+ - mmu notifier called with updated hva
+ - look up affected sptes through reverse map
+ - drop (or update) translations
+
+Emulating cr0.wp
+================
+
+If tdp is not enabled, the host must keep cr0.wp=1 so page write protection
+works for the guest kernel, not guest guest userspace. When the guest
+cr0.wp=1, this does not present a problem. However when the guest cr0.wp=0,
+we cannot map the permissions for gpte.u=1, gpte.w=0 to any spte (the
+semantics require allowing any guest kernel access plus user read access).
+
+We handle this by mapping the permissions to two possible sptes, depending
+on fault type:
+
+- kernel write fault: spte.u=0, spte.w=1 (allows full kernel access,
+ disallows user access)
+- read fault: spte.u=1, spte.w=0 (allows full read access, disallows kernel
+ write access)
+
+(user write faults generate a #PF)
+
+In the first case there is an additional complication if CR4.SMEP is
+enabled: since we've turned the page into a kernel page, the kernel may now
+execute it. We handle this by also setting spte.nx. If we get a user
+fetch or read fault, we'll change spte.u=1 and spte.nx=gpte.nx back.
+
+To prevent an spte that was converted into a kernel page with cr0.wp=0
+from being written by the kernel after cr0.wp has changed to 1, we make
+the value of cr0.wp part of the page role. This means that an spte created
+with one value of cr0.wp cannot be used when cr0.wp has a different value -
+it will simply be missed by the shadow page lookup code. A similar issue
+exists when an spte created with cr0.wp=0 and cr4.smep=0 is used after
+changing cr4.smep to 1. To avoid this, the value of !cr0.wp && cr4.smep
+is also made a part of the page role.
+
+Large pages
+===========
+
+The mmu supports all combinations of large and small guest and host pages.
+Supported page sizes include 4k, 2M, 4M, and 1G. 4M pages are treated as
+two separate 2M pages, on both guest and host, since the mmu always uses PAE
+paging.
+
+To instantiate a large spte, four constraints must be satisfied:
+
+- the spte must point to a large host page
+- the guest pte must be a large pte of at least equivalent size (if tdp is
+ enabled, there is no guest pte and this condition is satisified)
+- if the spte will be writeable, the large page frame may not overlap any
+ write-protected pages
+- the guest page must be wholly contained by a single memory slot
+
+To check the last two conditions, the mmu maintains a ->write_count set of
+arrays for each memory slot and large page size. Every write protected page
+causes its write_count to be incremented, thus preventing instantiation of
+a large spte. The frames at the end of an unaligned memory slot have
+artificically inflated ->write_counts so they can never be instantiated.
+
+Further reading
+===============
+
+- NPT presentation from KVM Forum 2008
+ http://www.linux-kvm.org/wiki/images/c/c8/KvmForum2008%24kdf2008_21.pdf
+
diff --git a/Documentation/virtual/kvm/msr.txt b/Documentation/virtual/kvm/msr.txt
new file mode 100644
index 00000000000..50317809113
--- /dev/null
+++ b/Documentation/virtual/kvm/msr.txt
@@ -0,0 +1,221 @@
+KVM-specific MSRs.
+Glauber Costa <glommer@redhat.com>, Red Hat Inc, 2010
+=====================================================
+
+KVM makes use of some custom MSRs to service some requests.
+
+Custom MSRs have a range reserved for them, that goes from
+0x4b564d00 to 0x4b564dff. There are MSRs outside this area,
+but they are deprecated and their use is discouraged.
+
+Custom MSR list
+--------
+
+The current supported Custom MSR list is:
+
+MSR_KVM_WALL_CLOCK_NEW: 0x4b564d00
+
+ data: 4-byte alignment physical address of a memory area which must be
+ in guest RAM. This memory is expected to hold a copy of the following
+ structure:
+
+ struct pvclock_wall_clock {
+ u32 version;
+ u32 sec;
+ u32 nsec;
+ } __attribute__((__packed__));
+
+ whose data will be filled in by the hypervisor. The hypervisor is only
+ guaranteed to update this data at the moment of MSR write.
+ Users that want to reliably query this information more than once have
+ to write more than once to this MSR. Fields have the following meanings:
+
+ version: guest has to check version before and after grabbing
+ time information and check that they are both equal and even.
+ An odd version indicates an in-progress update.
+
+ sec: number of seconds for wallclock.
+
+ nsec: number of nanoseconds for wallclock.
+
+ Note that although MSRs are per-CPU entities, the effect of this
+ particular MSR is global.
+
+ Availability of this MSR must be checked via bit 3 in 0x4000001 cpuid
+ leaf prior to usage.
+
+MSR_KVM_SYSTEM_TIME_NEW: 0x4b564d01
+
+ data: 4-byte aligned physical address of a memory area which must be in
+ guest RAM, plus an enable bit in bit 0. This memory is expected to hold
+ a copy of the following structure:
+
+ struct pvclock_vcpu_time_info {
+ u32 version;
+ u32 pad0;
+ u64 tsc_timestamp;
+ u64 system_time;
+ u32 tsc_to_system_mul;
+ s8 tsc_shift;
+ u8 flags;
+ u8 pad[2];
+ } __attribute__((__packed__)); /* 32 bytes */
+
+ whose data will be filled in by the hypervisor periodically. Only one
+ write, or registration, is needed for each VCPU. The interval between
+ updates of this structure is arbitrary and implementation-dependent.
+ The hypervisor may update this structure at any time it sees fit until
+ anything with bit0 == 0 is written to it.
+
+ Fields have the following meanings:
+
+ version: guest has to check version before and after grabbing
+ time information and check that they are both equal and even.
+ An odd version indicates an in-progress update.
+
+ tsc_timestamp: the tsc value at the current VCPU at the time
+ of the update of this structure. Guests can subtract this value
+ from current tsc to derive a notion of elapsed time since the
+ structure update.
+
+ system_time: a host notion of monotonic time, including sleep
+ time at the time this structure was last updated. Unit is
+ nanoseconds.
+
+ tsc_to_system_mul: a function of the tsc frequency. One has
+ to multiply any tsc-related quantity by this value to get
+ a value in nanoseconds, besides dividing by 2^tsc_shift
+
+ tsc_shift: cycle to nanosecond divider, as a power of two, to
+ allow for shift rights. One has to shift right any tsc-related
+ quantity by this value to get a value in nanoseconds, besides
+ multiplying by tsc_to_system_mul.
+
+ With this information, guests can derive per-CPU time by
+ doing:
+
+ time = (current_tsc - tsc_timestamp)
+ time = (time * tsc_to_system_mul) >> tsc_shift
+ time = time + system_time
+
+ flags: bits in this field indicate extended capabilities
+ coordinated between the guest and the hypervisor. Availability
+ of specific flags has to be checked in 0x40000001 cpuid leaf.
+ Current flags are:
+
+ flag bit | cpuid bit | meaning
+ -------------------------------------------------------------
+ | | time measures taken across
+ 0 | 24 | multiple cpus are guaranteed to
+ | | be monotonic
+ -------------------------------------------------------------
+
+ Availability of this MSR must be checked via bit 3 in 0x4000001 cpuid
+ leaf prior to usage.
+
+
+MSR_KVM_WALL_CLOCK: 0x11
+
+ data and functioning: same as MSR_KVM_WALL_CLOCK_NEW. Use that instead.
+
+ This MSR falls outside the reserved KVM range and may be removed in the
+ future. Its usage is deprecated.
+
+ Availability of this MSR must be checked via bit 0 in 0x4000001 cpuid
+ leaf prior to usage.
+
+MSR_KVM_SYSTEM_TIME: 0x12
+
+ data and functioning: same as MSR_KVM_SYSTEM_TIME_NEW. Use that instead.
+
+ This MSR falls outside the reserved KVM range and may be removed in the
+ future. Its usage is deprecated.
+
+ Availability of this MSR must be checked via bit 0 in 0x4000001 cpuid
+ leaf prior to usage.
+
+ The suggested algorithm for detecting kvmclock presence is then:
+
+ if (!kvm_para_available()) /* refer to cpuid.txt */
+ return NON_PRESENT;
+
+ flags = cpuid_eax(0x40000001);
+ if (flags & 3) {
+ msr_kvm_system_time = MSR_KVM_SYSTEM_TIME_NEW;
+ msr_kvm_wall_clock = MSR_KVM_WALL_CLOCK_NEW;
+ return PRESENT;
+ } else if (flags & 0) {
+ msr_kvm_system_time = MSR_KVM_SYSTEM_TIME;
+ msr_kvm_wall_clock = MSR_KVM_WALL_CLOCK;
+ return PRESENT;
+ } else
+ return NON_PRESENT;
+
+MSR_KVM_ASYNC_PF_EN: 0x4b564d02
+ data: Bits 63-6 hold 64-byte aligned physical address of a
+ 64 byte memory area which must be in guest RAM and must be
+ zeroed. Bits 5-2 are reserved and should be zero. Bit 0 is 1
+ when asynchronous page faults are enabled on the vcpu 0 when
+ disabled. Bit 2 is 1 if asynchronous page faults can be injected
+ when vcpu is in cpl == 0.
+
+ First 4 byte of 64 byte memory location will be written to by
+ the hypervisor at the time of asynchronous page fault (APF)
+ injection to indicate type of asynchronous page fault. Value
+ of 1 means that the page referred to by the page fault is not
+ present. Value 2 means that the page is now available. Disabling
+ interrupt inhibits APFs. Guest must not enable interrupt
+ before the reason is read, or it may be overwritten by another
+ APF. Since APF uses the same exception vector as regular page
+ fault guest must reset the reason to 0 before it does
+ something that can generate normal page fault. If during page
+ fault APF reason is 0 it means that this is regular page
+ fault.
+
+ During delivery of type 1 APF cr2 contains a token that will
+ be used to notify a guest when missing page becomes
+ available. When page becomes available type 2 APF is sent with
+ cr2 set to the token associated with the page. There is special
+ kind of token 0xffffffff which tells vcpu that it should wake
+ up all processes waiting for APFs and no individual type 2 APFs
+ will be sent.
+
+ If APF is disabled while there are outstanding APFs, they will
+ not be delivered.
+
+ Currently type 2 APF will be always delivered on the same vcpu as
+ type 1 was, but guest should not rely on that.
+
+MSR_KVM_STEAL_TIME: 0x4b564d03
+
+ data: 64-byte alignment physical address of a memory area which must be
+ in guest RAM, plus an enable bit in bit 0. This memory is expected to
+ hold a copy of the following structure:
+
+ struct kvm_steal_time {
+ __u64 steal;
+ __u32 version;
+ __u32 flags;
+ __u32 pad[12];
+ }
+
+ whose data will be filled in by the hypervisor periodically. Only one
+ write, or registration, is needed for each VCPU. The interval between
+ updates of this structure is arbitrary and implementation-dependent.
+ The hypervisor may update this structure at any time it sees fit until
+ anything with bit0 == 0 is written to it. Guest is required to make sure
+ this structure is initialized to zero.
+
+ Fields have the following meanings:
+
+ version: a sequence counter. In other words, guest has to check
+ this field before and after grabbing time information and make
+ sure they are both equal and even. An odd version indicates an
+ in-progress update.
+
+ flags: At this point, always zero. May be used to indicate
+ changes in this structure in the future.
+
+ steal: the amount of time in which this vCPU did not run, in
+ nanoseconds. Time during which the vcpu is idle, will not be
+ reported as steal time.
diff --git a/Documentation/virtual/kvm/nested-vmx.txt b/Documentation/virtual/kvm/nested-vmx.txt
new file mode 100644
index 00000000000..8ed937de116
--- /dev/null
+++ b/Documentation/virtual/kvm/nested-vmx.txt
@@ -0,0 +1,251 @@
+Nested VMX
+==========
+
+Overview
+---------
+
+On Intel processors, KVM uses Intel's VMX (Virtual-Machine eXtensions)
+to easily and efficiently run guest operating systems. Normally, these guests
+*cannot* themselves be hypervisors running their own guests, because in VMX,
+guests cannot use VMX instructions.
+
+The "Nested VMX" feature adds this missing capability - of running guest
+hypervisors (which use VMX) with their own nested guests. It does so by
+allowing a guest to use VMX instructions, and correctly and efficiently
+emulating them using the single level of VMX available in the hardware.
+
+We describe in much greater detail the theory behind the nested VMX feature,
+its implementation and its performance characteristics, in the OSDI 2010 paper
+"The Turtles Project: Design and Implementation of Nested Virtualization",
+available at:
+
+ http://www.usenix.org/events/osdi10/tech/full_papers/Ben-Yehuda.pdf
+
+
+Terminology
+-----------
+
+Single-level virtualization has two levels - the host (KVM) and the guests.
+In nested virtualization, we have three levels: The host (KVM), which we call
+L0, the guest hypervisor, which we call L1, and its nested guest, which we
+call L2.
+
+
+Known limitations
+-----------------
+
+The current code supports running Linux guests under KVM guests.
+Only 64-bit guest hypervisors are supported.
+
+Additional patches for running Windows under guest KVM, and Linux under
+guest VMware server, and support for nested EPT, are currently running in
+the lab, and will be sent as follow-on patchsets.
+
+
+Running nested VMX
+------------------
+
+The nested VMX feature is disabled by default. It can be enabled by giving
+the "nested=1" option to the kvm-intel module.
+
+No modifications are required to user space (qemu). However, qemu's default
+emulated CPU type (qemu64) does not list the "VMX" CPU feature, so it must be
+explicitly enabled, by giving qemu one of the following options:
+
+ -cpu host (emulated CPU has all features of the real CPU)
+
+ -cpu qemu64,+vmx (add just the vmx feature to a named CPU type)
+
+
+ABIs
+----
+
+Nested VMX aims to present a standard and (eventually) fully-functional VMX
+implementation for the a guest hypervisor to use. As such, the official
+specification of the ABI that it provides is Intel's VMX specification,
+namely volume 3B of their "Intel 64 and IA-32 Architectures Software
+Developer's Manual". Not all of VMX's features are currently fully supported,
+but the goal is to eventually support them all, starting with the VMX features
+which are used in practice by popular hypervisors (KVM and others).
+
+As a VMX implementation, nested VMX presents a VMCS structure to L1.
+As mandated by the spec, other than the two fields revision_id and abort,
+this structure is *opaque* to its user, who is not supposed to know or care
+about its internal structure. Rather, the structure is accessed through the
+VMREAD and VMWRITE instructions.
+Still, for debugging purposes, KVM developers might be interested to know the
+internals of this structure; This is struct vmcs12 from arch/x86/kvm/vmx.c.
+
+The name "vmcs12" refers to the VMCS that L1 builds for L2. In the code we
+also have "vmcs01", the VMCS that L0 built for L1, and "vmcs02" is the VMCS
+which L0 builds to actually run L2 - how this is done is explained in the
+aforementioned paper.
+
+For convenience, we repeat the content of struct vmcs12 here. If the internals
+of this structure changes, this can break live migration across KVM versions.
+VMCS12_REVISION (from vmx.c) should be changed if struct vmcs12 or its inner
+struct shadow_vmcs is ever changed.
+
+ typedef u64 natural_width;
+ struct __packed vmcs12 {
+ /* According to the Intel spec, a VMCS region must start with
+ * these two user-visible fields */
+ u32 revision_id;
+ u32 abort;
+
+ u32 launch_state; /* set to 0 by VMCLEAR, to 1 by VMLAUNCH */
+ u32 padding[7]; /* room for future expansion */
+
+ u64 io_bitmap_a;
+ u64 io_bitmap_b;
+ u64 msr_bitmap;
+ u64 vm_exit_msr_store_addr;
+ u64 vm_exit_msr_load_addr;
+ u64 vm_entry_msr_load_addr;
+ u64 tsc_offset;
+ u64 virtual_apic_page_addr;
+ u64 apic_access_addr;
+ u64 ept_pointer;
+ u64 guest_physical_address;
+ u64 vmcs_link_pointer;
+ u64 guest_ia32_debugctl;
+ u64 guest_ia32_pat;
+ u64 guest_ia32_efer;
+ u64 guest_pdptr0;
+ u64 guest_pdptr1;
+ u64 guest_pdptr2;
+ u64 guest_pdptr3;
+ u64 host_ia32_pat;
+ u64 host_ia32_efer;
+ u64 padding64[8]; /* room for future expansion */
+ natural_width cr0_guest_host_mask;
+ natural_width cr4_guest_host_mask;
+ natural_width cr0_read_shadow;
+ natural_width cr4_read_shadow;
+ natural_width cr3_target_value0;
+ natural_width cr3_target_value1;
+ natural_width cr3_target_value2;
+ natural_width cr3_target_value3;
+ natural_width exit_qualification;
+ natural_width guest_linear_address;
+ natural_width guest_cr0;
+ natural_width guest_cr3;
+ natural_width guest_cr4;
+ natural_width guest_es_base;
+ natural_width guest_cs_base;
+ natural_width guest_ss_base;
+ natural_width guest_ds_base;
+ natural_width guest_fs_base;
+ natural_width guest_gs_base;
+ natural_width guest_ldtr_base;
+ natural_width guest_tr_base;
+ natural_width guest_gdtr_base;
+ natural_width guest_idtr_base;
+ natural_width guest_dr7;
+ natural_width guest_rsp;
+ natural_width guest_rip;
+ natural_width guest_rflags;
+ natural_width guest_pending_dbg_exceptions;
+ natural_width guest_sysenter_esp;
+ natural_width guest_sysenter_eip;
+ natural_width host_cr0;
+ natural_width host_cr3;
+ natural_width host_cr4;
+ natural_width host_fs_base;
+ natural_width host_gs_base;
+ natural_width host_tr_base;
+ natural_width host_gdtr_base;
+ natural_width host_idtr_base;
+ natural_width host_ia32_sysenter_esp;
+ natural_width host_ia32_sysenter_eip;
+ natural_width host_rsp;
+ natural_width host_rip;
+ natural_width paddingl[8]; /* room for future expansion */
+ u32 pin_based_vm_exec_control;
+ u32 cpu_based_vm_exec_control;
+ u32 exception_bitmap;
+ u32 page_fault_error_code_mask;
+ u32 page_fault_error_code_match;
+ u32 cr3_target_count;
+ u32 vm_exit_controls;
+ u32 vm_exit_msr_store_count;
+ u32 vm_exit_msr_load_count;
+ u32 vm_entry_controls;
+ u32 vm_entry_msr_load_count;
+ u32 vm_entry_intr_info_field;
+ u32 vm_entry_exception_error_code;
+ u32 vm_entry_instruction_len;
+ u32 tpr_threshold;
+ u32 secondary_vm_exec_control;
+ u32 vm_instruction_error;
+ u32 vm_exit_reason;
+ u32 vm_exit_intr_info;
+ u32 vm_exit_intr_error_code;
+ u32 idt_vectoring_info_field;
+ u32 idt_vectoring_error_code;
+ u32 vm_exit_instruction_len;
+ u32 vmx_instruction_info;
+ u32 guest_es_limit;
+ u32 guest_cs_limit;
+ u32 guest_ss_limit;
+ u32 guest_ds_limit;
+ u32 guest_fs_limit;
+ u32 guest_gs_limit;
+ u32 guest_ldtr_limit;
+ u32 guest_tr_limit;
+ u32 guest_gdtr_limit;
+ u32 guest_idtr_limit;
+ u32 guest_es_ar_bytes;
+ u32 guest_cs_ar_bytes;
+ u32 guest_ss_ar_bytes;
+ u32 guest_ds_ar_bytes;
+ u32 guest_fs_ar_bytes;
+ u32 guest_gs_ar_bytes;
+ u32 guest_ldtr_ar_bytes;
+ u32 guest_tr_ar_bytes;
+ u32 guest_interruptibility_info;
+ u32 guest_activity_state;
+ u32 guest_sysenter_cs;
+ u32 host_ia32_sysenter_cs;
+ u32 padding32[8]; /* room for future expansion */
+ u16 virtual_processor_id;
+ u16 guest_es_selector;
+ u16 guest_cs_selector;
+ u16 guest_ss_selector;
+ u16 guest_ds_selector;
+ u16 guest_fs_selector;
+ u16 guest_gs_selector;
+ u16 guest_ldtr_selector;
+ u16 guest_tr_selector;
+ u16 host_es_selector;
+ u16 host_cs_selector;
+ u16 host_ss_selector;
+ u16 host_ds_selector;
+ u16 host_fs_selector;
+ u16 host_gs_selector;
+ u16 host_tr_selector;
+ };
+
+
+Authors
+-------
+
+These patches were written by:
+ Abel Gordon, abelg <at> il.ibm.com
+ Nadav Har'El, nyh <at> il.ibm.com
+ Orit Wasserman, oritw <at> il.ibm.com
+ Ben-Ami Yassor, benami <at> il.ibm.com
+ Muli Ben-Yehuda, muli <at> il.ibm.com
+
+With contributions by:
+ Anthony Liguori, aliguori <at> us.ibm.com
+ Mike Day, mdday <at> us.ibm.com
+ Michael Factor, factor <at> il.ibm.com
+ Zvi Dubitzky, dubi <at> il.ibm.com
+
+And valuable reviews by:
+ Avi Kivity, avi <at> redhat.com
+ Gleb Natapov, gleb <at> redhat.com
+ Marcelo Tosatti, mtosatti <at> redhat.com
+ Kevin Tian, kevin.tian <at> intel.com
+ and others.
diff --git a/Documentation/virtual/kvm/ppc-pv.txt b/Documentation/virtual/kvm/ppc-pv.txt
new file mode 100644
index 00000000000..2b7ce190cde
--- /dev/null
+++ b/Documentation/virtual/kvm/ppc-pv.txt
@@ -0,0 +1,198 @@
+The PPC KVM paravirtual interface
+=================================
+
+The basic execution principle by which KVM on PowerPC works is to run all kernel
+space code in PR=1 which is user space. This way we trap all privileged
+instructions and can emulate them accordingly.
+
+Unfortunately that is also the downfall. There are quite some privileged
+instructions that needlessly return us to the hypervisor even though they
+could be handled differently.
+
+This is what the PPC PV interface helps with. It takes privileged instructions
+and transforms them into unprivileged ones with some help from the hypervisor.
+This cuts down virtualization costs by about 50% on some of my benchmarks.
+
+The code for that interface can be found in arch/powerpc/kernel/kvm*
+
+Querying for existence
+======================
+
+To find out if we're running on KVM or not, we leverage the device tree. When
+Linux is running on KVM, a node /hypervisor exists. That node contains a
+compatible property with the value "linux,kvm".
+
+Once you determined you're running under a PV capable KVM, you can now use
+hypercalls as described below.
+
+KVM hypercalls
+==============
+
+Inside the device tree's /hypervisor node there's a property called
+'hypercall-instructions'. This property contains at most 4 opcodes that make
+up the hypercall. To call a hypercall, just call these instructions.
+
+The parameters are as follows:
+
+ Register IN OUT
+
+ r0 - volatile
+ r3 1st parameter Return code
+ r4 2nd parameter 1st output value
+ r5 3rd parameter 2nd output value
+ r6 4th parameter 3rd output value
+ r7 5th parameter 4th output value
+ r8 6th parameter 5th output value
+ r9 7th parameter 6th output value
+ r10 8th parameter 7th output value
+ r11 hypercall number 8th output value
+ r12 - volatile
+
+Hypercall definitions are shared in generic code, so the same hypercall numbers
+apply for x86 and powerpc alike with the exception that each KVM hypercall
+also needs to be ORed with the KVM vendor code which is (42 << 16).
+
+Return codes can be as follows:
+
+ Code Meaning
+
+ 0 Success
+ 12 Hypercall not implemented
+ <0 Error
+
+The magic page
+==============
+
+To enable communication between the hypervisor and guest there is a new shared
+page that contains parts of supervisor visible register state. The guest can
+map this shared page using the KVM hypercall KVM_HC_PPC_MAP_MAGIC_PAGE.
+
+With this hypercall issued the guest always gets the magic page mapped at the
+desired location. The first parameter indicates the effective address when the
+MMU is enabled. The second parameter indicates the address in real mode, if
+applicable to the target. For now, we always map the page to -4096. This way we
+can access it using absolute load and store functions. The following
+instruction reads the first field of the magic page:
+
+ ld rX, -4096(0)
+
+The interface is designed to be extensible should there be need later to add
+additional registers to the magic page. If you add fields to the magic page,
+also define a new hypercall feature to indicate that the host can give you more
+registers. Only if the host supports the additional features, make use of them.
+
+The magic page has the following layout as described in
+arch/powerpc/include/asm/kvm_para.h:
+
+struct kvm_vcpu_arch_shared {
+ __u64 scratch1;
+ __u64 scratch2;
+ __u64 scratch3;
+ __u64 critical; /* Guest may not get interrupts if == r1 */
+ __u64 sprg0;
+ __u64 sprg1;
+ __u64 sprg2;
+ __u64 sprg3;
+ __u64 srr0;
+ __u64 srr1;
+ __u64 dar;
+ __u64 msr;
+ __u32 dsisr;
+ __u32 int_pending; /* Tells the guest if we have an interrupt */
+};
+
+Additions to the page must only occur at the end. Struct fields are always 32
+or 64 bit aligned, depending on them being 32 or 64 bit wide respectively.
+
+Magic page features
+===================
+
+When mapping the magic page using the KVM hypercall KVM_HC_PPC_MAP_MAGIC_PAGE,
+a second return value is passed to the guest. This second return value contains
+a bitmap of available features inside the magic page.
+
+The following enhancements to the magic page are currently available:
+
+ KVM_MAGIC_FEAT_SR Maps SR registers r/w in the magic page
+
+For enhanced features in the magic page, please check for the existence of the
+feature before using them!
+
+MSR bits
+========
+
+The MSR contains bits that require hypervisor intervention and bits that do
+not require direct hypervisor intervention because they only get interpreted
+when entering the guest or don't have any impact on the hypervisor's behavior.
+
+The following bits are safe to be set inside the guest:
+
+ MSR_EE
+ MSR_RI
+ MSR_CR
+ MSR_ME
+
+If any other bit changes in the MSR, please still use mtmsr(d).
+
+Patched instructions
+====================
+
+The "ld" and "std" instructions are transormed to "lwz" and "stw" instructions
+respectively on 32 bit systems with an added offset of 4 to accommodate for big
+endianness.
+
+The following is a list of mapping the Linux kernel performs when running as
+guest. Implementing any of those mappings is optional, as the instruction traps
+also act on the shared page. So calling privileged instructions still works as
+before.
+
+From To
+==== ==
+
+mfmsr rX ld rX, magic_page->msr
+mfsprg rX, 0 ld rX, magic_page->sprg0
+mfsprg rX, 1 ld rX, magic_page->sprg1
+mfsprg rX, 2 ld rX, magic_page->sprg2
+mfsprg rX, 3 ld rX, magic_page->sprg3
+mfsrr0 rX ld rX, magic_page->srr0
+mfsrr1 rX ld rX, magic_page->srr1
+mfdar rX ld rX, magic_page->dar
+mfdsisr rX lwz rX, magic_page->dsisr
+
+mtmsr rX std rX, magic_page->msr
+mtsprg 0, rX std rX, magic_page->sprg0
+mtsprg 1, rX std rX, magic_page->sprg1
+mtsprg 2, rX std rX, magic_page->sprg2
+mtsprg 3, rX std rX, magic_page->sprg3
+mtsrr0 rX std rX, magic_page->srr0
+mtsrr1 rX std rX, magic_page->srr1
+mtdar rX std rX, magic_page->dar
+mtdsisr rX stw rX, magic_page->dsisr
+
+tlbsync nop
+
+mtmsrd rX, 0 b <special mtmsr section>
+mtmsr rX b <special mtmsr section>
+
+mtmsrd rX, 1 b <special mtmsrd section>
+
+[Book3S only]
+mtsrin rX, rY b <special mtsrin section>
+
+[BookE only]
+wrteei [0|1] b <special wrteei section>
+
+
+Some instructions require more logic to determine what's going on than a load
+or store instruction can deliver. To enable patching of those, we keep some
+RAM around where we can live translate instructions to. What happens is the
+following:
+
+ 1) copy emulation code to memory
+ 2) patch that code to fit the emulated instruction
+ 3) patch that code to return to the original pc + 4
+ 4) patch the original instruction to branch to the new code
+
+That way we can inject an arbitrary amount of code as replacement for a single
+instruction. This allows us to check for pending interrupts when setting EE=1
+for example.
diff --git a/Documentation/virtual/kvm/review-checklist.txt b/Documentation/virtual/kvm/review-checklist.txt
new file mode 100644
index 00000000000..a850986ed68
--- /dev/null
+++ b/Documentation/virtual/kvm/review-checklist.txt
@@ -0,0 +1,38 @@
+Review checklist for kvm patches
+================================
+
+1. The patch must follow Documentation/CodingStyle and
+ Documentation/SubmittingPatches.
+
+2. Patches should be against kvm.git master branch.
+
+3. If the patch introduces or modifies a new userspace API:
+ - the API must be documented in Documentation/virtual/kvm/api.txt
+ - the API must be discoverable using KVM_CHECK_EXTENSION
+
+4. New state must include support for save/restore.
+
+5. New features must default to off (userspace should explicitly request them).
+ Performance improvements can and should default to on.
+
+6. New cpu features should be exposed via KVM_GET_SUPPORTED_CPUID2
+
+7. Emulator changes should be accompanied by unit tests for qemu-kvm.git
+ kvm/test directory.
+
+8. Changes should be vendor neutral when possible. Changes to common code
+ are better than duplicating changes to vendor code.
+
+9. Similarly, prefer changes to arch independent code than to arch dependent
+ code.
+
+10. User/kernel interfaces and guest/host interfaces must be 64-bit clean
+ (all variables and sizes naturally aligned on 64-bit; use specific types
+ only - u64 rather than ulong).
+
+11. New guest visible features must either be documented in a hardware manual
+ or be accompanied by documentation.
+
+12. Features must be robust against reset and kexec - for example, shared
+ host/guest memory must be unshared to prevent the host from writing to
+ guest memory that the guest has not reserved for this purpose.
diff --git a/Documentation/virtual/kvm/timekeeping.txt b/Documentation/virtual/kvm/timekeeping.txt
new file mode 100644
index 00000000000..df8946377cb
--- /dev/null
+++ b/Documentation/virtual/kvm/timekeeping.txt
@@ -0,0 +1,612 @@
+
+ Timekeeping Virtualization for X86-Based Architectures
+
+ Zachary Amsden <zamsden@redhat.com>
+ Copyright (c) 2010, Red Hat. All rights reserved.
+
+1) Overview
+2) Timing Devices
+3) TSC Hardware
+4) Virtualization Problems
+
+=========================================================================
+
+1) Overview
+
+One of the most complicated parts of the X86 platform, and specifically,
+the virtualization of this platform is the plethora of timing devices available
+and the complexity of emulating those devices. In addition, virtualization of
+time introduces a new set of challenges because it introduces a multiplexed
+division of time beyond the control of the guest CPU.
+
+First, we will describe the various timekeeping hardware available, then
+present some of the problems which arise and solutions available, giving
+specific recommendations for certain classes of KVM guests.
+
+The purpose of this document is to collect data and information relevant to
+timekeeping which may be difficult to find elsewhere, specifically,
+information relevant to KVM and hardware-based virtualization.
+
+=========================================================================
+
+2) Timing Devices
+
+First we discuss the basic hardware devices available. TSC and the related
+KVM clock are special enough to warrant a full exposition and are described in
+the following section.
+
+2.1) i8254 - PIT
+
+One of the first timer devices available is the programmable interrupt timer,
+or PIT. The PIT has a fixed frequency 1.193182 MHz base clock and three
+channels which can be programmed to deliver periodic or one-shot interrupts.
+These three channels can be configured in different modes and have individual
+counters. Channel 1 and 2 were not available for general use in the original
+IBM PC, and historically were connected to control RAM refresh and the PC
+speaker. Now the PIT is typically integrated as part of an emulated chipset
+and a separate physical PIT is not used.
+
+The PIT uses I/O ports 0x40 - 0x43. Access to the 16-bit counters is done
+using single or multiple byte access to the I/O ports. There are 6 modes
+available, but not all modes are available to all timers, as only timer 2
+has a connected gate input, required for modes 1 and 5. The gate line is
+controlled by port 61h, bit 0, as illustrated in the following diagram.
+
+ -------------- ----------------
+| | | |
+| 1.1932 MHz |---------->| CLOCK OUT | ---------> IRQ 0
+| Clock | | | |
+ -------------- | +->| GATE TIMER 0 |
+ | ----------------
+ |
+ | ----------------
+ | | |
+ |------>| CLOCK OUT | ---------> 66.3 KHZ DRAM
+ | | | (aka /dev/null)
+ | +->| GATE TIMER 1 |
+ | ----------------
+ |
+ | ----------------
+ | | |
+ |------>| CLOCK OUT | ---------> Port 61h, bit 5
+ | | |
+Port 61h, bit 0 ---------->| GATE TIMER 2 | \_.---- ____
+ ---------------- _| )--|LPF|---Speaker
+ / *---- \___/
+Port 61h, bit 1 -----------------------------------/
+
+The timer modes are now described.
+
+Mode 0: Single Timeout. This is a one-shot software timeout that counts down
+ when the gate is high (always true for timers 0 and 1). When the count
+ reaches zero, the output goes high.
+
+Mode 1: Triggered One-shot. The output is initially set high. When the gate
+ line is set high, a countdown is initiated (which does not stop if the gate is
+ lowered), during which the output is set low. When the count reaches zero,
+ the output goes high.
+
+Mode 2: Rate Generator. The output is initially set high. When the countdown
+ reaches 1, the output goes low for one count and then returns high. The value
+ is reloaded and the countdown automatically resumes. If the gate line goes
+ low, the count is halted. If the output is low when the gate is lowered, the
+ output automatically goes high (this only affects timer 2).
+
+Mode 3: Square Wave. This generates a high / low square wave. The count
+ determines the length of the pulse, which alternates between high and low
+ when zero is reached. The count only proceeds when gate is high and is
+ automatically reloaded on reaching zero. The count is decremented twice at
+ each clock to generate a full high / low cycle at the full periodic rate.
+ If the count is even, the clock remains high for N/2 counts and low for N/2
+ counts; if the clock is odd, the clock is high for (N+1)/2 counts and low
+ for (N-1)/2 counts. Only even values are latched by the counter, so odd
+ values are not observed when reading. This is the intended mode for timer 2,
+ which generates sine-like tones by low-pass filtering the square wave output.
+
+Mode 4: Software Strobe. After programming this mode and loading the counter,
+ the output remains high until the counter reaches zero. Then the output
+ goes low for 1 clock cycle and returns high. The counter is not reloaded.
+ Counting only occurs when gate is high.
+
+Mode 5: Hardware Strobe. After programming and loading the counter, the
+ output remains high. When the gate is raised, a countdown is initiated
+ (which does not stop if the gate is lowered). When the counter reaches zero,
+ the output goes low for 1 clock cycle and then returns high. The counter is
+ not reloaded.
+
+In addition to normal binary counting, the PIT supports BCD counting. The
+command port, 0x43 is used to set the counter and mode for each of the three
+timers.
+
+PIT commands, issued to port 0x43, using the following bit encoding:
+
+Bit 7-4: Command (See table below)
+Bit 3-1: Mode (000 = Mode 0, 101 = Mode 5, 11X = undefined)
+Bit 0 : Binary (0) / BCD (1)
+
+Command table:
+
+0000 - Latch Timer 0 count for port 0x40
+ sample and hold the count to be read in port 0x40;
+ additional commands ignored until counter is read;
+ mode bits ignored.
+
+0001 - Set Timer 0 LSB mode for port 0x40
+ set timer to read LSB only and force MSB to zero;
+ mode bits set timer mode
+
+0010 - Set Timer 0 MSB mode for port 0x40
+ set timer to read MSB only and force LSB to zero;
+ mode bits set timer mode
+
+0011 - Set Timer 0 16-bit mode for port 0x40
+ set timer to read / write LSB first, then MSB;
+ mode bits set timer mode
+
+0100 - Latch Timer 1 count for port 0x41 - as described above
+0101 - Set Timer 1 LSB mode for port 0x41 - as described above
+0110 - Set Timer 1 MSB mode for port 0x41 - as described above
+0111 - Set Timer 1 16-bit mode for port 0x41 - as described above
+
+1000 - Latch Timer 2 count for port 0x42 - as described above
+1001 - Set Timer 2 LSB mode for port 0x42 - as described above
+1010 - Set Timer 2 MSB mode for port 0x42 - as described above
+1011 - Set Timer 2 16-bit mode for port 0x42 as described above
+
+1101 - General counter latch
+ Latch combination of counters into corresponding ports
+ Bit 3 = Counter 2
+ Bit 2 = Counter 1
+ Bit 1 = Counter 0
+ Bit 0 = Unused
+
+1110 - Latch timer status
+ Latch combination of counter mode into corresponding ports
+ Bit 3 = Counter 2
+ Bit 2 = Counter 1
+ Bit 1 = Counter 0
+
+ The output of ports 0x40-0x42 following this command will be:
+
+ Bit 7 = Output pin
+ Bit 6 = Count loaded (0 if timer has expired)
+ Bit 5-4 = Read / Write mode
+ 01 = MSB only
+ 10 = LSB only
+ 11 = LSB / MSB (16-bit)
+ Bit 3-1 = Mode
+ Bit 0 = Binary (0) / BCD mode (1)
+
+2.2) RTC
+
+The second device which was available in the original PC was the MC146818 real
+time clock. The original device is now obsolete, and usually emulated by the
+system chipset, sometimes by an HPET and some frankenstein IRQ routing.
+
+The RTC is accessed through CMOS variables, which uses an index register to
+control which bytes are read. Since there is only one index register, read
+of the CMOS and read of the RTC require lock protection (in addition, it is
+dangerous to allow userspace utilities such as hwclock to have direct RTC
+access, as they could corrupt kernel reads and writes of CMOS memory).
+
+The RTC generates an interrupt which is usually routed to IRQ 8. The interrupt
+can function as a periodic timer, an additional once a day alarm, and can issue
+interrupts after an update of the CMOS registers by the MC146818 is complete.
+The type of interrupt is signalled in the RTC status registers.
+
+The RTC will update the current time fields by battery power even while the
+system is off. The current time fields should not be read while an update is
+in progress, as indicated in the status register.
+
+The clock uses a 32.768kHz crystal, so bits 6-4 of register A should be
+programmed to a 32kHz divider if the RTC is to count seconds.
+
+This is the RAM map originally used for the RTC/CMOS:
+
+Location Size Description
+------------------------------------------
+00h byte Current second (BCD)
+01h byte Seconds alarm (BCD)
+02h byte Current minute (BCD)
+03h byte Minutes alarm (BCD)
+04h byte Current hour (BCD)
+05h byte Hours alarm (BCD)
+06h byte Current day of week (BCD)
+07h byte Current day of month (BCD)
+08h byte Current month (BCD)
+09h byte Current year (BCD)
+0Ah byte Register A
+ bit 7 = Update in progress
+ bit 6-4 = Divider for clock
+ 000 = 4.194 MHz
+ 001 = 1.049 MHz
+ 010 = 32 kHz
+ 10X = test modes
+ 110 = reset / disable
+ 111 = reset / disable
+ bit 3-0 = Rate selection for periodic interrupt
+ 000 = periodic timer disabled
+ 001 = 3.90625 uS
+ 010 = 7.8125 uS
+ 011 = .122070 mS
+ 100 = .244141 mS
+ ...
+ 1101 = 125 mS
+ 1110 = 250 mS
+ 1111 = 500 mS
+0Bh byte Register B
+ bit 7 = Run (0) / Halt (1)
+ bit 6 = Periodic interrupt enable
+ bit 5 = Alarm interrupt enable
+ bit 4 = Update-ended interrupt enable
+ bit 3 = Square wave interrupt enable
+ bit 2 = BCD calendar (0) / Binary (1)
+ bit 1 = 12-hour mode (0) / 24-hour mode (1)
+ bit 0 = 0 (DST off) / 1 (DST enabled)
+OCh byte Register C (read only)
+ bit 7 = interrupt request flag (IRQF)
+ bit 6 = periodic interrupt flag (PF)
+ bit 5 = alarm interrupt flag (AF)
+ bit 4 = update interrupt flag (UF)
+ bit 3-0 = reserved
+ODh byte Register D (read only)
+ bit 7 = RTC has power
+ bit 6-0 = reserved
+32h byte Current century BCD (*)
+ (*) location vendor specific and now determined from ACPI global tables
+
+2.3) APIC
+
+On Pentium and later processors, an on-board timer is available to each CPU
+as part of the Advanced Programmable Interrupt Controller. The APIC is
+accessed through memory-mapped registers and provides interrupt service to each
+CPU, used for IPIs and local timer interrupts.
+
+Although in theory the APIC is a safe and stable source for local interrupts,
+in practice, many bugs and glitches have occurred due to the special nature of
+the APIC CPU-local memory-mapped hardware. Beware that CPU errata may affect
+the use of the APIC and that workarounds may be required. In addition, some of
+these workarounds pose unique constraints for virtualization - requiring either
+extra overhead incurred from extra reads of memory-mapped I/O or additional
+functionality that may be more computationally expensive to implement.
+
+Since the APIC is documented quite well in the Intel and AMD manuals, we will
+avoid repetition of the detail here. It should be pointed out that the APIC
+timer is programmed through the LVT (local vector timer) register, is capable
+of one-shot or periodic operation, and is based on the bus clock divided down
+by the programmable divider register.
+
+2.4) HPET
+
+HPET is quite complex, and was originally intended to replace the PIT / RTC
+support of the X86 PC. It remains to be seen whether that will be the case, as
+the de facto standard of PC hardware is to emulate these older devices. Some
+systems designated as legacy free may support only the HPET as a hardware timer
+device.
+
+The HPET spec is rather loose and vague, requiring at least 3 hardware timers,
+but allowing implementation freedom to support many more. It also imposes no
+fixed rate on the timer frequency, but does impose some extremal values on
+frequency, error and slew.
+
+In general, the HPET is recommended as a high precision (compared to PIT /RTC)
+time source which is independent of local variation (as there is only one HPET
+in any given system). The HPET is also memory-mapped, and its presence is
+indicated through ACPI tables by the BIOS.
+
+Detailed specification of the HPET is beyond the current scope of this
+document, as it is also very well documented elsewhere.
+
+2.5) Offboard Timers
+
+Several cards, both proprietary (watchdog boards) and commonplace (e1000) have
+timing chips built into the cards which may have registers which are accessible
+to kernel or user drivers. To the author's knowledge, using these to generate
+a clocksource for a Linux or other kernel has not yet been attempted and is in
+general frowned upon as not playing by the agreed rules of the game. Such a
+timer device would require additional support to be virtualized properly and is
+not considered important at this time as no known operating system does this.
+
+=========================================================================
+
+3) TSC Hardware
+
+The TSC or time stamp counter is relatively simple in theory; it counts
+instruction cycles issued by the processor, which can be used as a measure of
+time. In practice, due to a number of problems, it is the most complicated
+timekeeping device to use.
+
+The TSC is represented internally as a 64-bit MSR which can be read with the
+RDMSR, RDTSC, or RDTSCP (when available) instructions. In the past, hardware
+limitations made it possible to write the TSC, but generally on old hardware it
+was only possible to write the low 32-bits of the 64-bit counter, and the upper
+32-bits of the counter were cleared. Now, however, on Intel processors family
+0Fh, for models 3, 4 and 6, and family 06h, models e and f, this restriction
+has been lifted and all 64-bits are writable. On AMD systems, the ability to
+write the TSC MSR is not an architectural guarantee.
+
+The TSC is accessible from CPL-0 and conditionally, for CPL > 0 software by
+means of the CR4.TSD bit, which when enabled, disables CPL > 0 TSC access.
+
+Some vendors have implemented an additional instruction, RDTSCP, which returns
+atomically not just the TSC, but an indicator which corresponds to the
+processor number. This can be used to index into an array of TSC variables to
+determine offset information in SMP systems where TSCs are not synchronized.
+The presence of this instruction must be determined by consulting CPUID feature
+bits.
+
+Both VMX and SVM provide extension fields in the virtualization hardware which
+allows the guest visible TSC to be offset by a constant. Newer implementations
+promise to allow the TSC to additionally be scaled, but this hardware is not
+yet widely available.
+
+3.1) TSC synchronization
+
+The TSC is a CPU-local clock in most implementations. This means, on SMP
+platforms, the TSCs of different CPUs may start at different times depending
+on when the CPUs are powered on. Generally, CPUs on the same die will share
+the same clock, however, this is not always the case.
+
+The BIOS may attempt to resynchronize the TSCs during the poweron process and
+the operating system or other system software may attempt to do this as well.
+Several hardware limitations make the problem worse - if it is not possible to
+write the full 64-bits of the TSC, it may be impossible to match the TSC in
+newly arriving CPUs to that of the rest of the system, resulting in
+unsynchronized TSCs. This may be done by BIOS or system software, but in
+practice, getting a perfectly synchronized TSC will not be possible unless all
+values are read from the same clock, which generally only is possible on single
+socket systems or those with special hardware support.
+
+3.2) TSC and CPU hotplug
+
+As touched on already, CPUs which arrive later than the boot time of the system
+may not have a TSC value that is synchronized with the rest of the system.
+Either system software, BIOS, or SMM code may actually try to establish the TSC
+to a value matching the rest of the system, but a perfect match is usually not
+a guarantee. This can have the effect of bringing a system from a state where
+TSC is synchronized back to a state where TSC synchronization flaws, however
+small, may be exposed to the OS and any virtualization environment.
+
+3.3) TSC and multi-socket / NUMA
+
+Multi-socket systems, especially large multi-socket systems are likely to have
+individual clocksources rather than a single, universally distributed clock.
+Since these clocks are driven by different crystals, they will not have
+perfectly matched frequency, and temperature and electrical variations will
+cause the CPU clocks, and thus the TSCs to drift over time. Depending on the
+exact clock and bus design, the drift may or may not be fixed in absolute
+error, and may accumulate over time.
+
+In addition, very large systems may deliberately slew the clocks of individual
+cores. This technique, known as spread-spectrum clocking, reduces EMI at the
+clock frequency and harmonics of it, which may be required to pass FCC
+standards for telecommunications and computer equipment.
+
+It is recommended not to trust the TSCs to remain synchronized on NUMA or
+multiple socket systems for these reasons.
+
+3.4) TSC and C-states
+
+C-states, or idling states of the processor, especially C1E and deeper sleep
+states may be problematic for TSC as well. The TSC may stop advancing in such
+a state, resulting in a TSC which is behind that of other CPUs when execution
+is resumed. Such CPUs must be detected and flagged by the operating system
+based on CPU and chipset identifications.
+
+The TSC in such a case may be corrected by catching it up to a known external
+clocksource.
+
+3.5) TSC frequency change / P-states
+
+To make things slightly more interesting, some CPUs may change frequency. They
+may or may not run the TSC at the same rate, and because the frequency change
+may be staggered or slewed, at some points in time, the TSC rate may not be
+known other than falling within a range of values. In this case, the TSC will
+not be a stable time source, and must be calibrated against a known, stable,
+external clock to be a usable source of time.
+
+Whether the TSC runs at a constant rate or scales with the P-state is model
+dependent and must be determined by inspecting CPUID, chipset or vendor
+specific MSR fields.
+
+In addition, some vendors have known bugs where the P-state is actually
+compensated for properly during normal operation, but when the processor is
+inactive, the P-state may be raised temporarily to service cache misses from
+other processors. In such cases, the TSC on halted CPUs could advance faster
+than that of non-halted processors. AMD Turion processors are known to have
+this problem.
+
+3.6) TSC and STPCLK / T-states
+
+External signals given to the processor may also have the effect of stopping
+the TSC. This is typically done for thermal emergency power control to prevent
+an overheating condition, and typically, there is no way to detect that this
+condition has happened.
+
+3.7) TSC virtualization - VMX
+
+VMX provides conditional trapping of RDTSC, RDMSR, WRMSR and RDTSCP
+instructions, which is enough for full virtualization of TSC in any manner. In
+addition, VMX allows passing through the host TSC plus an additional TSC_OFFSET
+field specified in the VMCS. Special instructions must be used to read and
+write the VMCS field.
+
+3.8) TSC virtualization - SVM
+
+SVM provides conditional trapping of RDTSC, RDMSR, WRMSR and RDTSCP
+instructions, which is enough for full virtualization of TSC in any manner. In
+addition, SVM allows passing through the host TSC plus an additional offset
+field specified in the SVM control block.
+
+3.9) TSC feature bits in Linux
+
+In summary, there is no way to guarantee the TSC remains in perfect
+synchronization unless it is explicitly guaranteed by the architecture. Even
+if so, the TSCs in multi-sockets or NUMA systems may still run independently
+despite being locally consistent.
+
+The following feature bits are used by Linux to signal various TSC attributes,
+but they can only be taken to be meaningful for UP or single node systems.
+
+X86_FEATURE_TSC : The TSC is available in hardware
+X86_FEATURE_RDTSCP : The RDTSCP instruction is available
+X86_FEATURE_CONSTANT_TSC : The TSC rate is unchanged with P-states
+X86_FEATURE_NONSTOP_TSC : The TSC does not stop in C-states
+X86_FEATURE_TSC_RELIABLE : TSC sync checks are skipped (VMware)
+
+4) Virtualization Problems
+
+Timekeeping is especially problematic for virtualization because a number of
+challenges arise. The most obvious problem is that time is now shared between
+the host and, potentially, a number of virtual machines. Thus the virtual
+operating system does not run with 100% usage of the CPU, despite the fact that
+it may very well make that assumption. It may expect it to remain true to very
+exacting bounds when interrupt sources are disabled, but in reality only its
+virtual interrupt sources are disabled, and the machine may still be preempted
+at any time. This causes problems as the passage of real time, the injection
+of machine interrupts and the associated clock sources are no longer completely
+synchronized with real time.
+
+This same problem can occur on native harware to a degree, as SMM mode may
+steal cycles from the naturally on X86 systems when SMM mode is used by the
+BIOS, but not in such an extreme fashion. However, the fact that SMM mode may
+cause similar problems to virtualization makes it a good justification for
+solving many of these problems on bare metal.
+
+4.1) Interrupt clocking
+
+One of the most immediate problems that occurs with legacy operating systems
+is that the system timekeeping routines are often designed to keep track of
+time by counting periodic interrupts. These interrupts may come from the PIT
+or the RTC, but the problem is the same: the host virtualization engine may not
+be able to deliver the proper number of interrupts per second, and so guest
+time may fall behind. This is especially problematic if a high interrupt rate
+is selected, such as 1000 HZ, which is unfortunately the default for many Linux
+guests.
+
+There are three approaches to solving this problem; first, it may be possible
+to simply ignore it. Guests which have a separate time source for tracking
+'wall clock' or 'real time' may not need any adjustment of their interrupts to
+maintain proper time. If this is not sufficient, it may be necessary to inject
+additional interrupts into the guest in order to increase the effective
+interrupt rate. This approach leads to complications in extreme conditions,
+where host load or guest lag is too much to compensate for, and thus another
+solution to the problem has risen: the guest may need to become aware of lost
+ticks and compensate for them internally. Although promising in theory, the
+implementation of this policy in Linux has been extremely error prone, and a
+number of buggy variants of lost tick compensation are distributed across
+commonly used Linux systems.
+
+Windows uses periodic RTC clocking as a means of keeping time internally, and
+thus requires interrupt slewing to keep proper time. It does use a low enough
+rate (ed: is it 18.2 Hz?) however that it has not yet been a problem in
+practice.
+
+4.2) TSC sampling and serialization
+
+As the highest precision time source available, the cycle counter of the CPU
+has aroused much interest from developers. As explained above, this timer has
+many problems unique to its nature as a local, potentially unstable and
+potentially unsynchronized source. One issue which is not unique to the TSC,
+but is highlighted because of its very precise nature is sampling delay. By
+definition, the counter, once read is already old. However, it is also
+possible for the counter to be read ahead of the actual use of the result.
+This is a consequence of the superscalar execution of the instruction stream,
+which may execute instructions out of order. Such execution is called
+non-serialized. Forcing serialized execution is necessary for precise
+measurement with the TSC, and requires a serializing instruction, such as CPUID
+or an MSR read.
+
+Since CPUID may actually be virtualized by a trap and emulate mechanism, this
+serialization can pose a performance issue for hardware virtualization. An
+accurate time stamp counter reading may therefore not always be available, and
+it may be necessary for an implementation to guard against "backwards" reads of
+the TSC as seen from other CPUs, even in an otherwise perfectly synchronized
+system.
+
+4.3) Timespec aliasing
+
+Additionally, this lack of serialization from the TSC poses another challenge
+when using results of the TSC when measured against another time source. As
+the TSC is much higher precision, many possible values of the TSC may be read
+while another clock is still expressing the same value.
+
+That is, you may read (T,T+10) while external clock C maintains the same value.
+Due to non-serialized reads, you may actually end up with a range which
+fluctuates - from (T-1.. T+10). Thus, any time calculated from a TSC, but
+calibrated against an external value may have a range of valid values.
+Re-calibrating this computation may actually cause time, as computed after the
+calibration, to go backwards, compared with time computed before the
+calibration.
+
+This problem is particularly pronounced with an internal time source in Linux,
+the kernel time, which is expressed in the theoretically high resolution
+timespec - but which advances in much larger granularity intervals, sometimes
+at the rate of jiffies, and possibly in catchup modes, at a much larger step.
+
+This aliasing requires care in the computation and recalibration of kvmclock
+and any other values derived from TSC computation (such as TSC virtualization
+itself).
+
+4.4) Migration
+
+Migration of a virtual machine raises problems for timekeeping in two ways.
+First, the migration itself may take time, during which interrupts cannot be
+delivered, and after which, the guest time may need to be caught up. NTP may
+be able to help to some degree here, as the clock correction required is
+typically small enough to fall in the NTP-correctable window.
+
+An additional concern is that timers based off the TSC (or HPET, if the raw bus
+clock is exposed) may now be running at different rates, requiring compensation
+in some way in the hypervisor by virtualizing these timers. In addition,
+migrating to a faster machine may preclude the use of a passthrough TSC, as a
+faster clock cannot be made visible to a guest without the potential of time
+advancing faster than usual. A slower clock is less of a problem, as it can
+always be caught up to the original rate. KVM clock avoids these problems by
+simply storing multipliers and offsets against the TSC for the guest to convert
+back into nanosecond resolution values.
+
+4.5) Scheduling
+
+Since scheduling may be based on precise timing and firing of interrupts, the
+scheduling algorithms of an operating system may be adversely affected by
+virtualization. In theory, the effect is random and should be universally
+distributed, but in contrived as well as real scenarios (guest device access,
+causes of virtualization exits, possible context switch), this may not always
+be the case. The effect of this has not been well studied.
+
+In an attempt to work around this, several implementations have provided a
+paravirtualized scheduler clock, which reveals the true amount of CPU time for
+which a virtual machine has been running.
+
+4.6) Watchdogs
+
+Watchdog timers, such as the lock detector in Linux may fire accidentally when
+running under hardware virtualization due to timer interrupts being delayed or
+misinterpretation of the passage of real time. Usually, these warnings are
+spurious and can be ignored, but in some circumstances it may be necessary to
+disable such detection.
+
+4.7) Delays and precision timing
+
+Precise timing and delays may not be possible in a virtualized system. This
+can happen if the system is controlling physical hardware, or issues delays to
+compensate for slower I/O to and from devices. The first issue is not solvable
+in general for a virtualized system; hardware control software can't be
+adequately virtualized without a full real-time operating system, which would
+require an RT aware virtualization platform.
+
+The second issue may cause performance problems, but this is unlikely to be a
+significant issue. In many cases these delays may be eliminated through
+configuration or paravirtualization.
+
+4.8) Covert channels and leaks
+
+In addition to the above problems, time information will inevitably leak to the
+guest about the host in anything but a perfect implementation of virtualized
+time. This may allow the guest to infer the presence of a hypervisor (as in a
+red-pill type detection), and it may allow information to leak between guests
+by using CPU utilization itself as a signalling channel. Preventing such
+problems would require completely isolated virtual time which may not track
+real time any longer. This may be useful in certain security or QA contexts,
+but in general isn't recommended for real-world deployment scenarios.