libvirt: Provide VIR_MIGRATE_PARAM_PERSIST_XML during live migration

The VIR_MIGRATE_PARAM_PERSIST_XML parameter was introduced in libvirt
v1.3.4 and is used to provide the new persistent configuration for the
destination during a live migration:

https://libvirt.org/html/libvirt-libvirt-domain.html#VIR_MIGRATE_PARAM_PERSIST_XML

Without this parameter the persistent configuration on the destination
will be the same as the original persistent configuration on the source
when the VIR_MIGRATE_PERSIST_DEST flag is provided.

As Nova does not currently provide the VIR_MIGRATE_PARAM_PERSIST_XML
param but does provide the VIR_MIGRATE_PERSIST_DEST flag this means that
a soft reboot by Nova of the instance after a live migration can revert
the domain back to the original persistent configuration from the
source.

Note that this is only possible in Nova as a soft reboot actually
results in the virDomainShutdown and virDomainLaunch libvirt APIs being
called that recreate the domain using the persistent configuration.
virDomainReboot does not result in this but is not called at this time.

The impact of this on the instance after the soft reboot is pretty
severe, host devices referenced in the original persistent configuration
on the source may not exist or could even be used by other users on the
destination. CPU and NUMA affinity could also differ drastically between
the two hosts resulting in the instance being unable to start etc.

As MIN_LIBVIRT_VERSION is now > v1.3.4 this change simply includes the
VIR_MIGRATE_PARAM_PERSIST_XML param using the same updated XML for the
destination as is already provided to VIR_MIGRATE_PARAM_DEST_XML.

Conflicts:
    nova/tests/unit/virt/libvirt/test_driver.py
    nova/virt/libvirt/driver.py

NOTE(melwitt): Conflicts in driver.py are because changes:

  I6ac601e633ab2b0a67b4802ff880865255188a93
    (libvirt: Provide VGPU inventory for a single GPU type)
  I947bf0ad34a48e9182a3dc016f47f0c9f71c9d7b
    ([libvirt] Allow multiple volume attachments)
  Ibfa64f18bbd2fb70db7791330ed1a64fe61c1355
    (libvirt: QEMU native LUKS decryption for encrypted volumes)
  If2035cac931c42c440d61ba97ebc7e9e92141a28
    (libvirt: Rework 'EBUSY' (SIGKILL) error handling code path)
  Ibf210dd27972fed2651d6c9bd73a0bcf352c8bab
    (libvirt: create vGPU for instance)

are not in Pike. Conflict in test_driver.py is because the Pike
backport of change I9b545ca8aa6dd7b41ddea2d333190c9fbed19bc1 explicitly
asserts byte string destination_xml in
_test_live_migration_block_migration_flags and the change is not in
Queens where this is being backported from.

Co-authored-by: Tadayoshi Hosoya <tad-hosoya@wr.jp.nec.com>
Closes-Bug: #1890501
Change-Id: Ia3f1d8e83cbc574ce5cb440032e12bbcb1e10e98
(cherry picked from commit 1bb8ee9)
(cherry picked from commit bbf9d1d)
(cherry picked from commit 6a07edb)
(cherry picked from commit b9ea91d)
(cherry picked from commit c438fd9)
(cherry picked from commit a721ca5)

nova/tests/unit/virt/libvirt/test_driver.py

@@ -8536,6 +8536,76 @@ def test_is_shared_block_storage_nfs(self):
                 'instance', data, block_device_info=bdi))
         self.assertEqual(0, mock_get_instance_disk_info.call_count)
 
+    @mock.patch.object(fakelibvirt.virDomain, "migrateToURI3")
+    @mock.patch('nova.virt.libvirt.migration.get_updated_guest_xml')
+    @mock.patch.object(fakelibvirt.Connection, 'getLibVersion')
+    def test_live_migration_persistent_xml(
+        self, mock_get_version, mock_get_updated_xml, mock_migrateToURI3):
+        """Assert that persistent_xml only provided when libvirt is >= v1.3.4
+        """
+        drvr = libvirt_driver.LibvirtDriver(fake.FakeVirtAPI(), False)
+        instance = self.test_instance
+        dest = '127.0.0.1'
+        block_migration = False
+        migrate_data = objects.LibvirtLiveMigrateData(
+            graphics_listen_addr_vnc='10.0.0.1',
+            graphics_listen_addr_spice='10.0.0.2',
+            serial_listen_addr='127.0.0.1',
+            target_connect_addr='127.0.0.1',
+            bdms=[],
+            block_migration=block_migration)
+        guest = libvirt_guest.Guest(fakelibvirt.virDomain)
+        device_names = ['vda']
+
+        mock_get_updated_xml.return_value = mock.sentinel.dest_xml
+
+        # persistent_xml was introduced in v1.3.4 so provide v1.3.3
+        v1_3_3 = versionutils.convert_version_to_int((1, 3, 3))
+        mock_get_version.return_value = v1_3_3
+
+        drvr._live_migration_operation(
+            self.context, instance, dest, block_migration, migrate_data,
+            guest, device_names)
+
+        expected_uri = drvr._live_migration_uri(dest)
+        expected_flags = 0
+        expected_params = {
+            'bandwidth': 0,
+            'destination_xml': mock.sentinel.dest_xml,
+            'migrate_disks': device_names,
+            'migrate_uri': 'tcp://127.0.0.1'
+        }
+
+        # Assert that migrateToURI3 is called without the persistent_xml param
+        mock_get_version.assert_called()
+        mock_migrateToURI3.assert_called_once_with(
+            expected_uri, params=expected_params, flags=expected_flags)
+
+        # reset mocks and try again with v1.3.4
+        mock_get_version.reset_mock()
+        mock_migrateToURI3.reset_mock()
+
+        # persistent_xml was introduced in v1.3.4 so provide it this time
+        v1_3_4 = versionutils.convert_version_to_int((1, 3, 4))
+        mock_get_version.return_value = v1_3_4
+
+        drvr._live_migration_operation(
+            self.context, instance, dest,
+            block_migration, migrate_data, guest, device_names)
+
+        expected_params = {
+            'bandwidth': 0,
+            'destination_xml': mock.sentinel.dest_xml,
+            'persistent_xml': mock.sentinel.dest_xml,
+            'migrate_disks': device_names,
+            'migrate_uri': 'tcp://127.0.0.1'
+        }
+
+        # Assert that migrateToURI3 is called with the persistent_xml param
+        mock_get_version.assert_called()
+        mock_migrateToURI3.assert_called_once_with(
+                expected_uri, params=expected_params, flags=expected_flags)
+
     def test_live_migration_update_graphics_xml(self):
         self.compute = manager.ComputeManager()
         instance_dict = dict(self.test_instance)
@@ -9059,19 +9129,21 @@ def test_live_migration_fails_without_serial_console_address(self):
 
     @mock.patch.object(host.Host, 'has_min_version', return_value=True)
     @mock.patch.object(fakelibvirt.virDomain, "migrateToURI3")
-    @mock.patch('nova.virt.libvirt.migration.get_updated_guest_xml',
-                return_value='')
+    @mock.patch('nova.virt.libvirt.migration.get_updated_guest_xml')
     @mock.patch('nova.virt.libvirt.guest.Guest.get_xml_desc',
                 return_value='<xml></xml>')
     def test_live_migration_uses_migrateToURI3(
             self, mock_old_xml, mock_new_xml, mock_migrateToURI3,
             mock_min_version):
+
+        mock_new_xml.return_value = mock.sentinel.new_xml
         # Preparing mocks
         disk_paths = ['vda', 'vdb']
         params = {
             'migrate_disks': ['vda', 'vdb'],
             'bandwidth': CONF.libvirt.live_migration_bandwidth,
-            'destination_xml': '',
+            'destination_xml': mock.sentinel.new_xml,
+            'persistent_xml': mock.sentinel.new_xml,
         }
         mock_migrateToURI3.side_effect = fakelibvirt.libvirtError("ERR")
 
@@ -9126,6 +9198,7 @@ def _test_live_migration_block_migration_flags(self,
             'migrate_disks': device_names,
             'bandwidth': CONF.libvirt.live_migration_bandwidth,
             'destination_xml': b'<xml/>',
+            'persistent_xml': b'<xml/>',
         }
         mock_migrateToURI3.assert_called_once_with(
             drvr._live_migration_uri('dest'), params=params,
@@ -9154,18 +9227,21 @@ def test_live_migration_block_migration_all_filtered(self):
 
     @mock.patch.object(host.Host, 'has_min_version', return_value=True)
     @mock.patch.object(fakelibvirt.virDomain, "migrateToURI3")
-    @mock.patch('nova.virt.libvirt.migration.get_updated_guest_xml',
-                return_value='')
+    @mock.patch('nova.virt.libvirt.migration.get_updated_guest_xml')
     @mock.patch('nova.virt.libvirt.guest.Guest.get_xml_desc', return_value='')
     def test_block_live_migration_tunnelled_migrateToURI3(
             self, mock_old_xml, mock_new_xml,
             mock_migrateToURI3, mock_min_version):
         self.flags(live_migration_tunnelled=True, group='libvirt')
+
+        mock_new_xml.return_value = mock.sentinel.new_xml
+
         # Preparing mocks
         disk_paths = []
         params = {
             'bandwidth': CONF.libvirt.live_migration_bandwidth,
-            'destination_xml': '',
+            'destination_xml': mock.sentinel.new_xml,
+            'persistent_xml': mock.sentinel.new_xml,
         }
         # Start test
         migrate_data = objects.LibvirtLiveMigrateData(

nova/virt/libvirt/driver.py

@@ -302,6 +302,11 @@ def repr_method(self):
                                 'mbmt': 'mbm_total',
                                }
 
+# libvirt >= v1.3.4 introduced VIR_MIGRATE_PARAM_PERSIST_XML that needs to be
+# provided when the VIR_MIGRATE_PERSIST_DEST flag is used to ensure the updated
+# domain XML is persisted on the destination.
+MIN_LIBVIRT_MIGRATE_PARAM_PERSIST_XML = (1, 3, 4)
+
 
 class LibvirtDriver(driver.ComputeDriver):
     capabilities = {
@@ -6519,6 +6524,12 @@ def _live_migration_operation(self, context, instance, dest,
                     libvirt.VIR_MIGRATE_TUNNELLED != 0):
                     params.pop('migrate_disks')
 
+                # NOTE(lyarwood): Only available from v1.3.4
+                if self._host.has_min_version(
+                    MIN_LIBVIRT_MIGRATE_PARAM_PERSIST_XML
+                ):
+                    params['persistent_xml'] = new_xml_str
+
             # TODO(sahid): This should be in
             # post_live_migration_at_source but no way to retrieve
             # ports acquired on the host for the guest at this