vfio/migration: Allow migration of multiple P2P supporting devices

Now that P2P support has been added to VFIO migration, allow migration
of multiple devices if all of them support P2P migration.

Single device migration is allowed regardless of P2P migration support.

Signed-off-by: Avihai Horon <avihaih@nvidia.com>
Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Tested-by: YangHang Liu <yanghliu@redhat.com>
Signed-off-by: Cédric Le Goater <clg@redhat.com>

hw/vfio/common.c

@@ -363,21 +363,31 @@ bool vfio_mig_active(void)
 
 static Error *multiple_devices_migration_blocker;
 
-static unsigned int vfio_migratable_device_num(void)
+/*
+ * Multiple devices migration is allowed only if all devices support P2P
+ * migration. Single device migration is allowed regardless of P2P migration
+ * support.
+ */
+static bool vfio_multiple_devices_migration_is_supported(void)
 {
     VFIOGroup *group;
     VFIODevice *vbasedev;
     unsigned int device_num = 0;
+    bool all_support_p2p = true;
 
     QLIST_FOREACH(group, &vfio_group_list, next) {
         QLIST_FOREACH(vbasedev, &group->device_list, next) {
             if (vbasedev->migration) {
                 device_num++;
+
+                if (!(vbasedev->migration->mig_flags & VFIO_MIGRATION_P2P)) {
+                    all_support_p2p = false;
+                }
             }
         }
     }
 
-    return device_num;
+    return all_support_p2p || device_num <= 1;
 }
 
 int vfio_block_multiple_devices_migration(VFIODevice *vbasedev, Error **errp)
@@ -385,19 +395,19 @@ int vfio_block_multiple_devices_migration(VFIODevice *vbasedev, Error **errp)
     int ret;
 
     if (multiple_devices_migration_blocker ||
-        vfio_migratable_device_num() <= 1) {
+        vfio_multiple_devices_migration_is_supported()) {
         return 0;
     }
 
     if (vbasedev->enable_migration == ON_OFF_AUTO_ON) {
-        error_setg(errp, "Migration is currently not supported with multiple "
+        error_setg(errp, "Multiple VFIO devices migration is supported only if "
-                         "VFIO devices");
+                         "all of them support P2P migration");
         return -EINVAL;
     }
 
     error_setg(&multiple_devices_migration_blocker,
-               "Migration is currently not supported with multiple "
+               "Multiple VFIO devices migration is supported only if all of "
-               "VFIO devices");
+               "them support P2P migration");
     ret = migrate_add_blocker(multiple_devices_migration_blocker, errp);
     if (ret < 0) {
         error_free(multiple_devices_migration_blocker);
@@ -410,7 +420,7 @@ int vfio_block_multiple_devices_migration(VFIODevice *vbasedev, Error **errp)
 void vfio_unblock_multiple_devices_migration(void)
 {
     if (!multiple_devices_migration_blocker ||
-        vfio_migratable_device_num() > 1) {
+        !vfio_multiple_devices_migration_is_supported()) {
         return;
     }