qemu: Use more data for comparing CPUs

With QEMU older than 2.9.0 libvirt uses CPUID instruction to determine
what CPU features are supported on the host. This was later used when
checking compatibility of guest CPUs. Since QEMU 2.9.0 we ask QEMU for
the host CPU data. But the two methods we use usually provide disjoint
sets of CPU features because QEMU/KVM does not support all features
provided by the host CPU and on the other hand it can enable some
feature even if the host CPU does not support them.

So if there is a domain which requires a CPU features disabled by
QEMU/KVM, libvirt will refuse to start it with QEMU > 2.9.0 as its guest
CPU is incompatible with the host CPU data we got from QEMU. But such
domain would happily start on older QEMU (of course, the features would
be missing the guest CPU). To fix this regression, we need to combine
both CPU feature sets when checking guest CPU compatibility.

https://bugzilla.redhat.com/show_bug.cgi?id=1439933

Signed-off-by: Jiri Denemark <jdenemar@redhat.com>

src/qemu/qemu_capabilities.c

@@ -386,6 +386,10 @@ struct _virQEMUCapsHostCPUData {
     virCPUDefPtr reported;
     /* Migratable host CPU definition used for updating guest CPU. */
     virCPUDefPtr migratable;
+    /* CPU definition with features detected by libvirt using virCPUGetHost
+     * combined with features reported by QEMU. This is used for backward
+     * compatible comparison between a guest CPU and a host CPU. */
+    virCPUDefPtr full;
 };
 
 /*
@@ -2142,6 +2146,10 @@ virQEMUCapsHostCPUDataCopy(virQEMUCapsHostCPUDataPtr dst,
         !(dst->migratable = virCPUDefCopy(src->migratable)))
         return -1;
 
+    if (src->full &&
+        !(dst->full = virCPUDefCopy(src->full)))
+        return -1;
+
     return 0;
 }
 
@@ -2152,6 +2160,7 @@ virQEMUCapsHostCPUDataClear(virQEMUCapsHostCPUDataPtr cpuData)
     qemuMonitorCPUModelInfoFree(cpuData->info);
     virCPUDefFree(cpuData->reported);
     virCPUDefFree(cpuData->migratable);
+    virCPUDefFree(cpuData->full);
 
     memset(cpuData, 0, sizeof(*cpuData));
 }
@@ -2493,6 +2502,11 @@ virQEMUCapsGetHostModel(virQEMUCapsPtr qemuCaps,
 
     case VIR_QEMU_CAPS_HOST_CPU_MIGRATABLE:
         return cpuData->migratable;
+
+    case VIR_QEMU_CAPS_HOST_CPU_FULL:
+        /* 'full' is non-NULL only if we have data from both QEMU and
+         * virCPUGetHost */
+        return cpuData->full ? cpuData->full : cpuData->reported;
     }
 
     return NULL;
@@ -2503,12 +2517,14 @@ static void
 virQEMUCapsSetHostModel(virQEMUCapsPtr qemuCaps,
                         virDomainVirtType type,
                         virCPUDefPtr reported,
-                        virCPUDefPtr migratable)
+                        virCPUDefPtr migratable,
+                        virCPUDefPtr full)
 {
     virQEMUCapsHostCPUDataPtr cpuData = virQEMUCapsGetHostCPUData(qemuCaps, type);
 
     cpuData->reported = reported;
     cpuData->migratable = migratable;
+    cpuData->full = full;
 }
 
 
@@ -3385,6 +3401,8 @@ virQEMUCapsInitHostCPUModel(virQEMUCapsPtr qemuCaps,
     virCPUDefPtr cpu = NULL;
     virCPUDefPtr migCPU = NULL;
     virCPUDefPtr hostCPU = NULL;
+    virCPUDefPtr fullCPU = NULL;
+    size_t i;
     int rc;
 
     if (!caps || !virQEMUCapsGuestIsNative(caps->host.arch, qemuCaps->arch))
@@ -3404,6 +3422,18 @@ virQEMUCapsInitHostCPUModel(virQEMUCapsPtr qemuCaps,
                                      virQEMUCapsCPUFilterFeatures,
                                      qemuCaps) < 0)
             goto error;
+    } else if (type == VIR_DOMAIN_VIRT_KVM &&
+               virCPUGetHostIsSupported(qemuCaps->arch)) {
+        if (!(fullCPU = virCPUGetHost(qemuCaps->arch, VIR_CPU_TYPE_GUEST,
+                                      NULL, NULL, 0)))
+            goto error;
+
+        for (i = 0; i < cpu->nfeatures; i++) {
+            if (cpu->features[i].policy == VIR_CPU_FEATURE_REQUIRE &&
+                virCPUDefUpdateFeature(fullCPU, cpu->features[i].name,
+                                       VIR_CPU_FEATURE_REQUIRE) < 0)
+                goto error;
+        }
     }
 
     if (!(migCPU = virQEMUCapsNewHostCPUModel()))
@@ -3419,7 +3449,7 @@ virQEMUCapsInitHostCPUModel(virQEMUCapsPtr qemuCaps,
             goto error;
     }
 
-    virQEMUCapsSetHostModel(qemuCaps, type, cpu, migCPU);
+    virQEMUCapsSetHostModel(qemuCaps, type, cpu, migCPU, fullCPU);
 
  cleanup:
     virCPUDefFree(hostCPU);
@@ -3428,6 +3458,7 @@ virQEMUCapsInitHostCPUModel(virQEMUCapsPtr qemuCaps,
  error:
     virCPUDefFree(cpu);
     virCPUDefFree(migCPU);
+    virCPUDefFree(fullCPU);
     virResetLastError();
     goto cleanup;
 }

src/qemu/qemu_capabilities.h

@@ -455,6 +455,10 @@ typedef enum {
     VIR_QEMU_CAPS_HOST_CPU_REPORTED,
     /* Migratable host CPU definition used for updating guest CPU. */
     VIR_QEMU_CAPS_HOST_CPU_MIGRATABLE,
+    /* CPU definition with features detected by libvirt using virCPUGetHost
+     * combined with features reported by QEMU. This is used for backward
+     * compatible comparison between a guest CPU and a host CPU. */
+    VIR_QEMU_CAPS_HOST_CPU_FULL,
 } virQEMUCapsHostCPUType;
 
 virCPUDefPtr virQEMUCapsGetHostModel(virQEMUCapsPtr qemuCaps,

src/qemu/qemu_process.c

@@ -5305,7 +5305,7 @@ qemuProcessUpdateGuestCPU(virDomainDefPtr def,
     if (def->cpu->check == VIR_CPU_CHECK_PARTIAL &&
         virCPUCompare(caps->host.arch,
                       virQEMUCapsGetHostModel(qemuCaps, def->virtType,
-                                              VIR_QEMU_CAPS_HOST_CPU_REPORTED),
+                                              VIR_QEMU_CAPS_HOST_CPU_FULL),
                       def->cpu, true) < 0)
         return -1;