Add compatibility for CPU model config with libvirt < 0.9.10

Libvirt versions prior to 0.9.10 do not support the simpler
'mode' attribute for choosing CPU model. So with such libvirt
releases we must explicitly construct the guest CPU model
from the host capabilities info when mode=host-model. We
can not support mode=host-passthrough at all with these
earlier libvirt versions

This change can be reverted in the future, if the value of
the MIN_LIBVIRT_VERSION constant is increased to 0.9.10
or later

Fixes: bug #1003373
Implements: blueprint libvirt-xml-cpu-model
Change-Id: I3e55ffccf38be18454f810efeb5c201aab94ddb0
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>

1 files changed, 40 insertions, 3 deletions

diff --git a/nova/virt/libvirt/driver.py b/nova/virt/libvirt/driver.py
index 950494d97..f41cdba8a 100644
--- a/nova/virt/libvirt/driver.py
+++ b/nova/virt/libvirt/driver.py
@@ -231,6 +231,9 @@ LIBVIRT_POWER_STATE = {
 }
 
 MIN_LIBVIRT_VERSION = (0, 9, 6)
+# When the above version matches/exceeds this version
+# delete it & corresponding code using it
+MIN_LIBVIRT_HOST_CPU_VERSION = (0, 9, 10)
 
 
 def _late_load_cheetah():
@@ -1469,6 +1472,27 @@ class LibvirtDriver(driver.ComputeDriver):
         caps.parse_str(xmlstr)
         return caps
 
+    def get_host_cpu_for_guest(self):
+        """Returns an instance of config.LibvirtConfigGuestCPU
+           representing the host's CPU model & topology with
+           policy for configuring a guest to match"""
+
+        caps = self.get_host_capabilities()
+        hostcpu = caps.host.cpu
+        guestcpu = config.LibvirtConfigGuestCPU()
+
+        guestcpu.model = hostcpu.model
+        guestcpu.vendor = hostcpu.vendor
+        guestcpu.arch = hostcpu.arch
+
+        guestcpu.match = "exact"
+
+        for hostfeat in hostcpu.features:
+            guestfeat = config.LibvirtConfigGuestCPUFeature(hostfeat.name)
+            guestfeat.policy = "require"
+
+        return guestcpu
+
     def get_guest_cpu_config(self):
         mode = FLAGS.libvirt_cpu_mode
         model = FLAGS.libvirt_cpu_model
@@ -1494,9 +1518,22 @@ class LibvirtDriver(driver.ComputeDriver):
         LOG.debug(_("CPU mode '%(mode)s' model '%(model)s' was chosen")
                   % {'mode': mode, 'model': (model or "")})
 
-        cpu = config.LibvirtConfigGuestCPU()
-        cpu.mode = mode
-        cpu.model = model
+        # TODO(berrange): in the future, when MIN_LIBVIRT_VERSION is
+        # updated to be at least this new, we can kill off the elif
+        # blocks here
+        if self.has_min_version(MIN_LIBVIRT_HOST_CPU_VERSION):
+            cpu = config.LibvirtConfigGuestCPU()
+            cpu.mode = mode
+            cpu.model = model
+        elif mode == "custom":
+            cpu = config.LibvirtConfigGuestCPU()
+            cpu.model = model
+        elif mode == "host-model":
+            cpu = self.get_host_cpu_for_guest()
+        elif mode == "host-passthrough":
+            msg = _("Passthrough of the host CPU was requested but "
+                    "this libvirt version does not support this feature")
+            raise exception.NovaException(msg)
 
         return cpu