qemu: cpu: fix "full" CPU to include all "reported" CPU features

On Core i5 650 x86_64 kvm guest fail to start with error [1] for next cpu config:

  <cpu mode='host-model' check='partial'>
    <model fallback='allow'/>
    <feature policy='require' name='x2apic'/>
  </cpu>

The problem is in full CPU calculation in virQEMUCapsInitHostCPUModel.
It is supposed to include features emulated by qemu and missed on host. Some of
such features may be not included however.

For Core i5 650  host CPU is detected as Westmere and reported CPU as
SandyBridge. x2apic is missed on host and provided by installed qemu. The
feature is not mentioned in reported CPU features explicitly because SandyBridge
model include it. As a result full CPU does not include x2apic too.

Solution is to expand guest cpu features before updating fullCPU features.

[1] error: the CPU is incompatible with host CPU: \
       Host CPU does not provide required features: x2apic
Signed-off-by: NNikolay Shirokovskiy <nshirokovskiy@virtuozzo.com>
Reviewed-by: NJiri Denemark <jdenemar@redhat.com>

src/qemu/qemu_capabilities.c

@@ -2702,6 +2702,7 @@ virQEMUCapsInitHostCPUModel(virQEMUCapsPtr qemuCaps,
                             virDomainVirtType type)
 {
     virCPUDefPtr cpu = NULL;
+    virCPUDefPtr cpuExpanded = NULL;
     virCPUDefPtr migCPU = NULL;
     virCPUDefPtr hostCPU = NULL;
     virCPUDefPtr fullCPU = NULL;
@@ -2736,9 +2737,13 @@ virQEMUCapsInitHostCPUModel(virQEMUCapsPtr qemuCaps,
                                       NULL, NULL)))
             goto error;
 
-        for (i = 0; i < cpu->nfeatures; i++) {
-            if (cpu->features[i].policy == VIR_CPU_FEATURE_REQUIRE &&
-                virCPUDefUpdateFeature(fullCPU, cpu->features[i].name,
+        if (!(cpuExpanded = virCPUDefCopy(cpu)) ||
+            virCPUExpandFeatures(qemuCaps->arch, cpuExpanded) < 0)
+            goto error;
+
+        for (i = 0; i < cpuExpanded->nfeatures; i++) {
+            if (cpuExpanded->features[i].policy == VIR_CPU_FEATURE_REQUIRE &&
+                virCPUDefUpdateFeature(fullCPU, cpuExpanded->features[i].name,
                                        VIR_CPU_FEATURE_REQUIRE) < 0)
                 goto error;
         }
@@ -2760,6 +2765,7 @@ virQEMUCapsInitHostCPUModel(virQEMUCapsPtr qemuCaps,
     virQEMUCapsSetHostModel(qemuCaps, type, cpu, migCPU, fullCPU);
 
  cleanup:
+    virCPUDefFree(cpuExpanded);
     virCPUDefFree(hostCPU);
     return;