qemu: Update CPU definition according to QEMU

When starting a domain with custom guest CPU specification QEMU may add
or remove some CPU features. There are several reasons for this, e.g.,
QEMU/KVM does not support some requested features or the definition of
the requested CPU model in libvirt's cpu_map.xml differs from the one
QEMU is using. We can't really avoid this because CPU models are allowed
to change with machine types and libvirt doesn't know (and probably
doesn't even want to know) about such changes.

Thus when we want to make sure guest ABI doesn't change when a domain
gets migrated to another host, we need to update our live CPU definition
according to the CPU QEMU created. Once updated, we will change CPU
checking to VIR_CPU_CHECK_FULL to make sure the virtual CPU created
after migration exactly matches the one on the source.

https://bugzilla.redhat.com/show_bug.cgi?id=822148
https://bugzilla.redhat.com/show_bug.cgi?id=824989

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

src/cpu/cpu.c

@@ -712,6 +712,50 @@ virCPUUpdate(virArch arch,
 }
 
 
+/**
+ * virCPUUpdateLive:
+ *
+ * @arch: CPU architecture
+ * @cpu: guest CPU definition to be updated
+ * @dataEnabled: CPU data of the virtual CPU
+ * @dataDisabled: CPU data with features requested by @cpu but disabled by the
+ *                hypervisor
+ *
+ * Update custom mode CPU according to the virtual CPU created by the
+ * hypervisor.
+ *
+ * Returns -1 on error,
+ *          0 when the CPU was successfully updated,
+ *          1 when the operation does not make sense on the CPU or it is not
+ *            supported for the given architecture.
+ */
+int
+virCPUUpdateLive(virArch arch,
+                 virCPUDefPtr cpu,
+                 virCPUDataPtr dataEnabled,
+                 virCPUDataPtr dataDisabled)
+{
+    struct cpuArchDriver *driver;
+
+    VIR_DEBUG("arch=%s, cpu=%p, dataEnabled=%p, dataDisabled=%p",
+              virArchToString(arch), cpu, dataEnabled, dataDisabled);
+
+    if (!(driver = cpuGetSubDriver(arch)))
+        return -1;
+
+    if (!driver->updateLive)
+        return 1;
+
+    if (cpu->mode != VIR_CPU_MODE_CUSTOM)
+        return 1;
+
+    if (driver->updateLive(cpu, dataEnabled, dataDisabled) < 0)
+        return -1;
+
+    return 0;
+}
+
+
 /**
  * virCPUCheckFeature:
  *

src/cpu/cpu.h

@@ -86,6 +86,11 @@ typedef int
 (*virCPUArchUpdate)(virCPUDefPtr guest,
                     const virCPUDef *host);
 
+typedef int
+(*virCPUArchUpdateLive)(virCPUDefPtr cpu,
+                        virCPUDataPtr dataEnabled,
+                        virCPUDataPtr dataDisabled);
+
 typedef int
 (*virCPUArchCheckFeature)(const virCPUDef *cpu,
                           const char *feature);
@@ -122,6 +127,7 @@ struct cpuArchDriver {
     virCPUArchGetHost   getHost;
     cpuArchBaseline     baseline;
     virCPUArchUpdate    update;
+    virCPUArchUpdateLive updateLive;
     virCPUArchCheckFeature checkFeature;
     virCPUArchDataCheckFeature dataCheckFeature;
     virCPUArchDataFormat dataFormat;
@@ -198,6 +204,12 @@ virCPUUpdate(virArch arch,
              const virCPUDef *host)
     ATTRIBUTE_NONNULL(2);
 
+int
+virCPUUpdateLive(virArch arch,
+                 virCPUDefPtr cpu,
+                 virCPUDataPtr dataEnabled,
+                 virCPUDataPtr dataDisabled)
+    ATTRIBUTE_NONNULL(2);
 
 int
 virCPUCheckFeature(virArch arch,

src/cpu/cpu_x86.c

@@ -2677,6 +2677,64 @@ virCPUx86Update(virCPUDefPtr guest,
 }
 
 
+static int
+virCPUx86UpdateLive(virCPUDefPtr cpu,
+                    virCPUDataPtr dataEnabled,
+                    virCPUDataPtr dataDisabled)
+{
+    virCPUx86MapPtr map;
+    virCPUx86ModelPtr model = NULL;
+    virCPUx86Data enabled = VIR_CPU_X86_DATA_INIT;
+    virCPUx86Data disabled = VIR_CPU_X86_DATA_INIT;
+    size_t i;
+    int ret = -1;
+
+    if (!(map = virCPUx86GetMap()))
+        return -1;
+
+    if (!(model = x86ModelFromCPU(cpu, map, -1)))
+        goto cleanup;
+
+    if (dataEnabled &&
+        x86DataCopy(&enabled, &dataEnabled->data.x86) < 0)
+        goto cleanup;
+
+    if (dataDisabled &&
+        x86DataCopy(&disabled, &dataDisabled->data.x86) < 0)
+        goto cleanup;
+
+    x86DataSubtract(&enabled, &model->data);
+
+    for (i = 0; i < map->nfeatures; i++) {
+        virCPUx86FeaturePtr feature = map->features[i];
+
+        if (x86DataIsSubset(&enabled, &feature->data)) {
+            VIR_DEBUG("Adding feature '%s' enabled by the hypervisor",
+                      feature->name);
+            if (virCPUDefUpdateFeature(cpu, feature->name,
+                                       VIR_CPU_FEATURE_REQUIRE) < 0)
+                goto cleanup;
+        }
+
+        if (x86DataIsSubset(&disabled, &feature->data)) {
+            VIR_DEBUG("Removing feature '%s' disabled by the hypervisor",
+                      feature->name);
+            if (virCPUDefUpdateFeature(cpu, feature->name,
+                                       VIR_CPU_FEATURE_DISABLE) < 0)
+                goto cleanup;
+        }
+    }
+
+    ret = 0;
+
+ cleanup:
+    x86ModelFree(model);
+    virCPUx86DataClear(&enabled);
+    virCPUx86DataClear(&disabled);
+    return ret;
+}
+
+
 static int
 virCPUx86CheckFeature(const virCPUDef *cpu,
                       const char *name)
@@ -2854,6 +2912,7 @@ struct cpuArchDriver cpuDriverX86 = {
 #endif
     .baseline   = x86Baseline,
     .update     = virCPUx86Update,
+    .updateLive = virCPUx86UpdateLive,
     .checkFeature = virCPUx86CheckFeature,
     .dataCheckFeature = virCPUx86DataCheckFeature,
     .dataFormat = virCPUx86DataFormat,

src/libvirt_private.syms

@@ -1016,6 +1016,7 @@ virCPUGetHost;
 virCPUGetModels;
 virCPUTranslate;
 virCPUUpdate;
+virCPUUpdateLive;
 
 
 # cpu/cpu_x86.h

src/qemu/qemu_process.c

@@ -3840,12 +3840,13 @@ qemuProcessVerifyCPUFeatures(virDomainDefPtr def,
 
 
 static int
-qemuProcessVerifyGuestCPU(virQEMUDriverPtr driver,
-                          virDomainObjPtr vm,
-                          qemuDomainAsyncJob asyncJob)
+qemuProcessUpdateLiveGuestCPU(virQEMUDriverPtr driver,
+                              virDomainObjPtr vm,
+                              qemuDomainAsyncJob asyncJob)
 {
     virDomainDefPtr def = vm->def;
     virCPUDataPtr cpu = NULL;
+    virCPUDataPtr disabled = NULL;
     qemuDomainObjPrivatePtr priv = vm->privateData;
     int rc;
     int ret = -1;
@@ -3854,7 +3855,7 @@ qemuProcessVerifyGuestCPU(virQEMUDriverPtr driver,
         if (qemuDomainObjEnterMonitorAsync(driver, vm, asyncJob) < 0)
             goto cleanup;
 
-        rc = qemuMonitorGetGuestCPU(priv->mon, def->os.arch, &cpu, NULL);
+        rc = qemuMonitorGetGuestCPU(priv->mon, def->os.arch, &cpu, &disabled);
 
         if (qemuDomainObjExitMonitor(driver, vm) < 0)
             goto cleanup;
@@ -3871,12 +3872,18 @@ qemuProcessVerifyGuestCPU(virQEMUDriverPtr driver,
 
         if (qemuProcessVerifyCPUFeatures(def, cpu) < 0)
             goto cleanup;
+
+        if ((rc = virCPUUpdateLive(def->os.arch, def->cpu, cpu, disabled)) < 0)
+            goto cleanup;
+        else if (rc == 0)
+            def->cpu->check = VIR_CPU_CHECK_FULL;
     }
 
     ret = 0;
 
  cleanup:
     virCPUDataFree(cpu);
+    virCPUDataFree(disabled);
     return ret;
 }
 
@@ -5720,8 +5727,8 @@ qemuProcessLaunch(virConnectPtr conn,
     if (qemuConnectAgent(driver, vm) < 0)
         goto cleanup;
 
-    VIR_DEBUG("Detecting if required emulator features are present");
-    if (qemuProcessVerifyGuestCPU(driver, vm, asyncJob) < 0)
+    VIR_DEBUG("Verifying and updating provided guest CPU");
+    if (qemuProcessUpdateLiveGuestCPU(driver, vm, asyncJob) < 0)
         goto cleanup;
 
     VIR_DEBUG("Setting up post-init cgroup restrictions");