libvirt: Fix the rescue race for vGPU instances

When rescuing an instance having a vGPU, we were not using the vGPU.
There would then be a race condition during the rescue where the vGPU
could be passed to another instance.
Instead, we should just make sure the vGPU would also be in the rescued
instance.

Change-Id: I7150e15694bb149ae67da37b5e43b6ea7507fe82
Closes-bug: #1762688
(cherry picked from commit 1c59397e09)

doc/source/admin/virtual-gpu.rst

@@ -172,7 +172,8 @@ Caveats
 
 .. note::
 
-       All the caveats are related to the Queens release
+   This information is correct as of the 17.0.0 Queens release. Where
+   improvements have been made or issues fixed, they are noted per item.
 
 For libvirt:
 
@@ -199,6 +200,8 @@ For libvirt:
   instance immediately after rescue. However, rebuilding the rescued instance
   only helps if there are other free vGPUs on the host.
 
+  .. note:: This has been resolved in the Rocky release [#]_.
+
 For XenServer:
 
 * Suspend and live migration with vGPUs attached depends on support from the
@@ -219,6 +222,7 @@ For XenServer:
   resize. If you want to migrate an instance, make sure to rebuild it after the
   migration.
 
+.. [#] https://bugs.launchpad.net/nova/+bug/1762688
 
 .. Links
 .. _Intel GVT-g: https://01.org/igvt-g

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

@@ -18811,6 +18811,8 @@ class LibvirtDriverTestCase(test.NoDBTestCase):
             self.drvr.detach_interface(self.context, instance, network_info[0])
         self.mox.VerifyAll()
 
+    @mock.patch('nova.virt.libvirt.LibvirtDriver.'
+                '_get_all_assigned_mediated_devices')
     @mock.patch('nova.virt.libvirt.utils.write_to_file')
     # NOTE(mdbooth): The following 4 mocks are required to execute
     #                get_guest_xml().
@@ -18822,11 +18824,14 @@ class LibvirtDriverTestCase(test.NoDBTestCase):
                      mock_instance_metadata, mock_supports_direct_io,
                      mock_build_device_metadata, mock_set_host_enabled,
                      mock_write_to_file,
+                     mock_get_mdev,
                      exists=None):
         self.flags(instances_path=self.useFixture(fixtures.TempDir()).path)
         mock_build_device_metadata.return_value = None
         mock_supports_direct_io.return_value = True
 
+        mock_get_mdev.return_value = {uuids.mdev1: uuids.inst1}
+
         backend = self.useFixture(
             fake_imagebackend.ImageBackendFixture(exists=exists))
 
@@ -18890,6 +18895,11 @@ class LibvirtDriverTestCase(test.NoDBTestCase):
         self.assertEqual(expected_kernel_ramdisk_paths,
                          kernel_ramdisk_paths)
 
+        # The generated domain XML should also contain any existing mdev
+        self.assertEqual(
+            [uuids.mdev1],
+            doc.xpath("devices/*[@type='mdev']/source/address/@uuid"))
+
     @mock.patch('nova.virt.configdrive.ConfigDriveBuilder._make_iso9660')
     def test_rescue_config_drive(self, mock_mkisofs):
         instance = self._create_instance({'config_drive': str(True)})

nova/virt/libvirt/driver.py

@@ -3013,11 +3013,16 @@ class LibvirtDriver(driver.ComputeDriver):
         gen_confdrive = functools.partial(self._create_configdrive,
                                           context, instance, injection_info,
                                           rescue=True)
+        # NOTE(sbauza): Since rescue recreates the guest XML, we need to
+        # remember the existing mdevs for reusing them.
+        mdevs = self._get_all_assigned_mediated_devices(instance)
+        mdevs = list(mdevs.keys())
         self._create_image(context, instance, disk_info['mapping'],
                            injection_info=injection_info, suffix='.rescue',
                            disk_images=rescue_images)
         xml = self._get_guest_xml(context, instance, network_info, disk_info,
-                                  image_meta, rescue=rescue_images)
+                                  image_meta, rescue=rescue_images,
+                                  mdevs=mdevs)
         self._destroy(instance)
         self._create_domain(xml, post_xml_callback=gen_confdrive)