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-*** BIG FAT WARNING ***
-The kvm module is currently in EXPERIMENTAL state for s390. This means that
-the interface to the module is not yet considered to remain stable. Thus, be
-prepared that we keep breaking your userspace application and guest
-compatibility over and over again until we feel happy with the result. Make sure
-your guest kernel, your host kernel, and your userspace launcher are in a
-consistent state.
-
-This Documentation describes the unique ioctl calls to /dev/kvm, the resulting
-kvm-vm file descriptors, and the kvm-vcpu file descriptors that differ from x86.
-
-1. ioctl calls to /dev/kvm
-KVM does support the following ioctls on s390 that are common with other
-architectures and do behave the same:
-KVM_GET_API_VERSION
-KVM_CREATE_VM (*) see note
-KVM_CHECK_EXTENSION
-KVM_GET_VCPU_MMAP_SIZE
-
-Notes:
-* KVM_CREATE_VM may fail on s390, if the calling process has multiple
-threads and has not called KVM_S390_ENABLE_SIE before.
-
-In addition, on s390 the following architecture specific ioctls are supported:
-ioctl: KVM_S390_ENABLE_SIE
-args: none
-see also: include/linux/kvm.h
-This call causes the kernel to switch on PGSTE in the user page table. This
-operation is needed in order to run a virtual machine, and it requires the
-calling process to be single-threaded. Note that the first call to KVM_CREATE_VM
-will implicitly try to switch on PGSTE if the user process has not called
-KVM_S390_ENABLE_SIE before. User processes that want to launch multiple threads
-before creating a virtual machine have to call KVM_S390_ENABLE_SIE, or will
-observe an error calling KVM_CREATE_VM. Switching on PGSTE is a one-time
-operation, is not reversible, and will persist over the entire lifetime of
-the calling process. It does not have any user-visible effect other than a small
-performance penalty.
-
-2. ioctl calls to the kvm-vm file descriptor
-KVM does support the following ioctls on s390 that are common with other
-architectures and do behave the same:
-KVM_CREATE_VCPU
-KVM_SET_USER_MEMORY_REGION (*) see note
-KVM_GET_DIRTY_LOG (**) see note
-
-Notes:
-* kvm does only allow exactly one memory slot on s390, which has to start
- at guest absolute address zero and at a user address that is aligned on any
- page boundary. This hardware "limitation" allows us to have a few unique
- optimizations. The memory slot doesn't have to be filled
- with memory actually, it may contain sparse holes. That said, with different
- user memory layout this does still allow a large flexibility when
- doing the guest memory setup.
-** KVM_GET_DIRTY_LOG doesn't work properly yet. The user will receive an empty
-log. This ioctl call is only needed for guest migration, and we intend to
-implement this one in the future.
-
-In addition, on s390 the following architecture specific ioctls for the kvm-vm
-file descriptor are supported:
-ioctl: KVM_S390_INTERRUPT
-args: struct kvm_s390_interrupt *
-see also: include/linux/kvm.h
-This ioctl is used to submit a floating interrupt for a virtual machine.
-Floating interrupts may be delivered to any virtual cpu in the configuration.
-Only some interrupt types defined in include/linux/kvm.h make sense when
-submitted as floating interrupts. The following interrupts are not considered
-to be useful as floating interrupts, and a call to inject them will result in
--EINVAL error code: program interrupts and interprocessor signals. Valid
-floating interrupts are:
-KVM_S390_INT_VIRTIO
-KVM_S390_INT_SERVICE
-
-3. ioctl calls to the kvm-vcpu file descriptor
-KVM does support the following ioctls on s390 that are common with other
-architectures and do behave the same:
-KVM_RUN
-KVM_GET_REGS
-KVM_SET_REGS
-KVM_GET_SREGS
-KVM_SET_SREGS
-KVM_GET_FPU
-KVM_SET_FPU
-
-In addition, on s390 the following architecture specific ioctls for the
-kvm-vcpu file descriptor are supported:
-ioctl: KVM_S390_INTERRUPT
-args: struct kvm_s390_interrupt *
-see also: include/linux/kvm.h
-This ioctl is used to submit an interrupt for a specific virtual cpu.
-Only some interrupt types defined in include/linux/kvm.h make sense when
-submitted for a specific cpu. The following interrupts are not considered
-to be useful, and a call to inject them will result in -EINVAL error code:
-service processor calls and virtio interrupts. Valid interrupt types are:
-KVM_S390_PROGRAM_INT
-KVM_S390_SIGP_STOP
-KVM_S390_RESTART
-KVM_S390_SIGP_SET_PREFIX
-KVM_S390_INT_EMERGENCY
-
-ioctl: KVM_S390_STORE_STATUS
-args: unsigned long
-see also: include/linux/kvm.h
-This ioctl stores the state of the cpu at the guest real address given as
-argument, unless one of the following values defined in include/linux/kvm.h
-is given as argument:
-KVM_S390_STORE_STATUS_NOADDR - the CPU stores its status to the save area in
-absolute lowcore as defined by the principles of operation
-KVM_S390_STORE_STATUS_PREFIXED - the CPU stores its status to the save area in
-its prefix page just like the dump tool that comes with zipl. This is useful
-to create a system dump for use with lkcdutils or crash.
-
-ioctl: KVM_S390_SET_INITIAL_PSW
-args: struct kvm_s390_psw *
-see also: include/linux/kvm.h
-This ioctl can be used to set the processor status word (psw) of a stopped cpu
-prior to running it with KVM_RUN. Note that this call is not required to modify
-the psw during sie intercepts that fall back to userspace because struct kvm_run
-does contain the psw, and this value is evaluated during reentry of KVM_RUN
-after the intercept exit was recognized.
-
-ioctl: KVM_S390_INITIAL_RESET
-args: none
-see also: include/linux/kvm.h
-This ioctl can be used to perform an initial cpu reset as defined by the
-principles of operation. The target cpu has to be in stopped state.