vfio/migration: Move from STOP_COPY to STOP in vfio_save_cleanup()

Changing the device state from STOP_COPY to STOP can take time as the
device may need to free resources and do other operations as part of the
transition. Currently, this is done in vfio_save_complete_precopy() and
therefore it is counted in the migration downtime.

To avoid this, change the device state from STOP_COPY to STOP in
vfio_save_cleanup(), which is called after migration has completed and
thus is not part of migration downtime.

Signed-off-by: Avihai Horon <avihaih@nvidia.com>
Tested-by: YangHang Liu <yanghliu@redhat.com>
Signed-off-by: Cédric Le Goater <clg@redhat.com>

hw/vfio/migration.c

@@ -383,6 +383,19 @@ static void vfio_save_cleanup(void *opaque)
     VFIODevice *vbasedev = opaque;
     VFIOMigration *migration = vbasedev->migration;
 
+    /*
+     * Changing device state from STOP_COPY to STOP can take time. Do it here,
+     * after migration has completed, so it won't increase downtime.
+     */
+    if (migration->device_state == VFIO_DEVICE_STATE_STOP_COPY) {
+        /*
+         * If setting the device in STOP state fails, the device should be
+         * reset. To do so, use ERROR state as a recover state.
+         */
+        vfio_migration_set_state(vbasedev, VFIO_DEVICE_STATE_STOP,
+                                 VFIO_DEVICE_STATE_ERROR);
+    }
+
     g_free(migration->data_buffer);
     migration->data_buffer = NULL;
     migration->precopy_init_size = 0;
@@ -508,12 +521,6 @@ static int vfio_save_complete_precopy(QEMUFile *f, void *opaque)
         return ret;
     }
 
-    /*
-     * If setting the device in STOP state fails, the device should be reset.
-     * To do so, use ERROR state as a recover state.
-     */
-    ret = vfio_migration_set_state(vbasedev, VFIO_DEVICE_STATE_STOP,
-                                   VFIO_DEVICE_STATE_ERROR);
     trace_vfio_save_complete_precopy(vbasedev->name, ret);
 
     return ret;