qemu: Use updated CPU when starting QEMU if possible

If QEMU is new enough and we have the live updated CPU definition in
either save or migration cookie, we can use it to enforce ABI. The
original guest CPU from domain XML will be stored in private data.

Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: Pavel Hrdina <phrdina@redhat.com>

src/qemu/qemu_domain.c

@@ -9240,3 +9240,43 @@ virSaveCookieCallbacks virQEMUDriverDomainSaveCookie = {
     .parse = qemuDomainSaveCookieParse,
     .format = qemuDomainSaveCookieFormat,
 };
+
+
+/**
+ * qemuDomainUpdateCPU:
+ * @vm: domain which is being started
+ * @cpu: CPU updated when the domain was running previously (before migration,
+ *       snapshot, or save)
+ * @origCPU: where to store the original CPU from vm->def in case @cpu was
+ *           used instead
+ *
+ * Replace the CPU definition with the updated one when QEMU is new enough to
+ * allow us to check extra features it is about to enable or disable when
+ * starting a domain. The original CPU is stored in @origCPU.
+ *
+ * Returns 0 on success, -1 on error.
+ */
+int
+qemuDomainUpdateCPU(virDomainObjPtr vm,
+                    virCPUDefPtr cpu,
+                    virCPUDefPtr *origCPU)
+{
+    qemuDomainObjPrivatePtr priv = vm->privateData;
+
+    *origCPU = NULL;
+
+    if (!cpu || !vm->def->cpu ||
+        !virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_QUERY_CPU_MODEL_EXPANSION) ||
+        virCPUDefIsEqual(vm->def->cpu, cpu, false))
+        return 0;
+
+    if (!(cpu = virCPUDefCopy(cpu)))
+        return -1;
+
+    VIR_DEBUG("Replacing CPU def with the updated one");
+
+    *origCPU = vm->def->cpu;
+    vm->def->cpu = cpu;
+
+    return 0;
+}

src/qemu/qemu_domain.h

@@ -919,4 +919,9 @@ char *qemuDomainDiskBackingStoreGetName(virDomainDiskDefPtr disk,
 virStorageSourcePtr qemuDomainGetStorageSourceByDevstr(const char *devstr,
                                                        virDomainDefPtr def);
 
+int
+qemuDomainUpdateCPU(virDomainObjPtr vm,
+                    virCPUDefPtr cpu,
+                    virCPUDefPtr *origCPU);
+
 #endif /* __QEMU_DOMAIN_H__ */

src/qemu/qemu_driver.c

@@ -1779,7 +1779,7 @@ static virDomainPtr qemuDomainCreateXML(virConnectPtr conn,
         goto cleanup;
     }
 
-    if (qemuProcessStart(conn, driver, vm, QEMU_ASYNC_JOB_START,
+    if (qemuProcessStart(conn, driver, vm, NULL, QEMU_ASYNC_JOB_START,
                          NULL, -1, NULL, NULL,
                          VIR_NETDEV_VPORT_PROFILE_OP_CREATE,
                          start_flags) < 0) {
@@ -6506,8 +6506,8 @@ qemuDomainSaveImageStartVM(virConnectPtr conn,
         }
     }
 
-    if (qemuProcessStart(conn, driver, vm, asyncJob,
+    if (qemuProcessStart(conn, driver, vm, cookie ? cookie->cpu : NULL,
-                         "stdio", *fd, path, NULL,
+                         asyncJob, "stdio", *fd, path, NULL,
                          VIR_NETDEV_VPORT_PROFILE_OP_RESTORE,
                          VIR_QEMU_PROCESS_START_PAUSED) == 0)
         restored = true;
@@ -7124,7 +7124,7 @@ qemuDomainObjStart(virConnectPtr conn,
         }
     }
 
-    ret = qemuProcessStart(conn, driver, vm, asyncJob,
+    ret = qemuProcessStart(conn, driver, vm, NULL, asyncJob,
                            NULL, -1, NULL, NULL,
                            VIR_NETDEV_VPORT_PROFILE_OP_CREATE, start_flags);
     virDomainAuditStart(vm, "booted", ret >= 0);
@@ -15294,6 +15294,8 @@ qemuDomainRevertToSnapshot(virDomainSnapshotPtr snapshot,
     virCapsPtr caps = NULL;
     bool was_running = false;
     bool was_stopped = false;
+    qemuDomainSaveCookiePtr cookie;
+    virCPUDefPtr origCPU = NULL;
 
     virCheckFlags(VIR_DOMAIN_SNAPSHOT_REVERT_RUNNING |
                   VIR_DOMAIN_SNAPSHOT_REVERT_PAUSED |
@@ -15399,6 +15401,8 @@ qemuDomainRevertToSnapshot(virDomainSnapshotPtr snapshot,
             goto endjob;
     }
 
+    cookie = (qemuDomainSaveCookiePtr) snap->def->cookie;
+
     switch ((virDomainState) snap->def->state) {
     case VIR_DOMAIN_RUNNING:
     case VIR_DOMAIN_PAUSED:
@@ -15410,6 +15414,15 @@ qemuDomainRevertToSnapshot(virDomainSnapshotPtr snapshot,
          * to have finer control.  */
         if (virDomainObjIsActive(vm)) {
             /* Transitions 5, 6, 8, 9 */
+            /* Replace the CPU in config and put the original one in priv
+             * once we're done.
+             */
+            if (cookie && cookie->cpu && config->cpu) {
+                origCPU = config->cpu;
+                if (!(config->cpu = virCPUDefCopy(cookie->cpu)))
+                    goto endjob;
+            }
+
             /* Check for ABI compatibility. We need to do this check against
              * the migratable XML or it will always fail otherwise */
             if (config &&
@@ -15469,8 +15482,11 @@ qemuDomainRevertToSnapshot(virDomainSnapshotPtr snapshot,
                  * failed loadvm attempt? */
                 goto endjob;
             }
-            if (config)
+            if (config) {
                 virDomainObjAssignDef(vm, config, false, NULL);
+                virCPUDefFree(priv->origCPU);
+                VIR_STEAL_PTR(priv->origCPU, origCPU);
+            }
         } else {
             /* Transitions 2, 3 */
         load:
@@ -15479,6 +15495,7 @@ qemuDomainRevertToSnapshot(virDomainSnapshotPtr snapshot,
                 virDomainObjAssignDef(vm, config, false, NULL);
 
             rc = qemuProcessStart(snapshot->domain->conn, driver, vm,
+                                  cookie ? cookie->cpu : NULL,
                                   QEMU_ASYNC_JOB_START, NULL, -1, NULL, snap,
                                   VIR_NETDEV_VPORT_PROFILE_OP_CREATE,
                                   VIR_QEMU_PROCESS_START_PAUSED);
@@ -15572,7 +15589,7 @@ qemuDomainRevertToSnapshot(virDomainSnapshotPtr snapshot,
             start_flags |= paused ? VIR_QEMU_PROCESS_START_PAUSED : 0;
 
             qemuDomainEventQueue(driver, event);
-            rc = qemuProcessStart(snapshot->domain->conn, driver, vm,
+            rc = qemuProcessStart(snapshot->domain->conn, driver, vm, NULL,
                                   QEMU_ASYNC_JOB_START, NULL, -1, NULL, NULL,
                                   VIR_NETDEV_VPORT_PROFILE_OP_CREATE,
                                   start_flags);
@@ -15644,6 +15661,7 @@ qemuDomainRevertToSnapshot(virDomainSnapshotPtr snapshot,
     virObjectUnref(caps);
     virObjectUnref(cfg);
     virNWFilterUnlockFilterUpdates();
+    virCPUDefFree(origCPU);
 
     return ret;
 }

src/qemu/qemu_migration.c

@@ -2681,7 +2681,7 @@ qemuMigrationPrepareAny(virQEMUDriverPtr driver,
         goto stopjob;
     }
 
-    if (qemuProcessInit(driver, vm, QEMU_ASYNC_JOB_MIGRATION_IN,
+    if (qemuProcessInit(driver, vm, mig->cpu, QEMU_ASYNC_JOB_MIGRATION_IN,
                         true, VIR_QEMU_PROCESS_START_AUTODESTROY) < 0)
         goto stopjob;
     stopProcess = true;

src/qemu/qemu_process.c

@@ -3946,6 +3946,13 @@ qemuProcessUpdateLiveGuestCPU(virQEMUDriverPtr driver,
         if (qemuProcessVerifyCPUFeatures(def, cpu) < 0)
             goto cleanup;
 
+        /* Don't update the CPU if we already did so when starting a domain
+         * during migration, restore or snapshot revert. */
+        if (priv->origCPU) {
+            ret = 0;
+            goto cleanup;
+        }
+
         if (!(orig = virCPUDefCopy(def->cpu)))
             goto cleanup;
 
@@ -4864,6 +4871,7 @@ qemuProcessStartValidate(virQEMUDriverPtr driver,
 int
 qemuProcessInit(virQEMUDriverPtr driver,
                 virDomainObjPtr vm,
+                virCPUDefPtr updatedCPU,
                 qemuDomainAsyncJob asyncJob,
                 bool migration,
                 unsigned int flags)
@@ -4872,6 +4880,7 @@ qemuProcessInit(virQEMUDriverPtr driver,
     virCapsPtr caps = NULL;
     qemuDomainObjPrivatePtr priv = vm->privateData;
     int stopFlags;
+    virCPUDefPtr origCPU = NULL;
     int ret = -1;
 
     VIR_DEBUG("vm=%p name=%s id=%d migration=%d",
@@ -4896,6 +4905,9 @@ qemuProcessInit(virQEMUDriverPtr driver,
                                                       vm->def->os.machine)))
         goto cleanup;
 
+    if (qemuDomainUpdateCPU(vm, updatedCPU, &origCPU) < 0)
+        goto cleanup;
+
     if (qemuProcessStartValidate(driver, vm, priv->qemuCaps, caps, flags) < 0)
         goto cleanup;
 
@@ -4928,11 +4940,14 @@ qemuProcessInit(virQEMUDriverPtr driver,
 
         if (qemuDomainSetPrivatePaths(driver, vm) < 0)
             goto stop;
+
+        VIR_STEAL_PTR(priv->origCPU, origCPU);
     }
 
     ret = 0;
 
  cleanup:
+    virCPUDefFree(origCPU);
     virObjectUnref(cfg);
     virObjectUnref(caps);
     return ret;
@@ -5963,6 +5978,7 @@ int
 qemuProcessStart(virConnectPtr conn,
                  virQEMUDriverPtr driver,
                  virDomainObjPtr vm,
+                 virCPUDefPtr updatedCPU,
                  qemuDomainAsyncJob asyncJob,
                  const char *migrateFrom,
                  int migrateFd,
@@ -5993,7 +6009,8 @@ qemuProcessStart(virConnectPtr conn,
     if (!migrateFrom && !snapshot)
         flags |= VIR_QEMU_PROCESS_START_NEW;
 
-    if (qemuProcessInit(driver, vm, asyncJob, !!migrateFrom, flags) < 0)
+    if (qemuProcessInit(driver, vm, updatedCPU,
+                        asyncJob, !!migrateFrom, flags) < 0)
         goto cleanup;
 
     if (migrateFrom) {
@@ -6072,7 +6089,8 @@ qemuProcessCreatePretendCmd(virConnectPtr conn,
     flags |= VIR_QEMU_PROCESS_START_PRETEND;
     flags |= VIR_QEMU_PROCESS_START_NEW;
 
-    if (qemuProcessInit(driver, vm, QEMU_ASYNC_JOB_NONE, !!migrateURI, flags) < 0)
+    if (qemuProcessInit(driver, vm, NULL, QEMU_ASYNC_JOB_NONE,
+                        !!migrateURI, flags) < 0)
         goto cleanup;
 
     if (qemuProcessPrepareDomain(conn, driver, vm, flags) < 0)
@@ -6476,6 +6494,8 @@ void qemuProcessStop(virQEMUDriverPtr driver,
 
     /* clean up migration data */
     VIR_FREE(priv->migTLSAlias);
+    virCPUDefFree(priv->origCPU);
+    priv->origCPU = NULL;
 
     /* clear previously used namespaces */
     virBitmapFree(priv->namespaces);

src/qemu/qemu_process.h

@@ -75,6 +75,7 @@ typedef enum {
 int qemuProcessStart(virConnectPtr conn,
                      virQEMUDriverPtr driver,
                      virDomainObjPtr vm,
+                     virCPUDefPtr updatedCPU,
                      qemuDomainAsyncJob asyncJob,
                      const char *migrateFrom,
                      int stdin_fd,
@@ -93,6 +94,7 @@ virCommandPtr qemuProcessCreatePretendCmd(virConnectPtr conn,
 
 int qemuProcessInit(virQEMUDriverPtr driver,
                     virDomainObjPtr vm,
+                    virCPUDefPtr updatedCPU,
                     qemuDomainAsyncJob asyncJob,
                     bool migration,
                     unsigned int flags);