drm/ttm: warn when resv objs are mixed in a bulk_move

The BOs in a bulk move must share all the same reservation object
to make sure that we lock the whole bulk during eviction.

Actually document and enforce that with a warning.
Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240312105555.3065-1-christian.koenig@amd.com

drivers/gpu/drm/ttm/ttm_resource.c

@@ -105,6 +105,7 @@ static void ttm_lru_bulk_move_add(struct ttm_lru_bulk_move *bulk,
 		pos->first = res;
 		pos->last = res;
 	} else {
+		WARN_ON(pos->first->bo->base.resv != res->bo->base.resv);
 		ttm_lru_bulk_move_pos_tail(pos, res);
 	}
 }

include/drm/ttm/ttm_resource.h

@@ -251,6 +251,9 @@ struct ttm_lru_bulk_move_pos {
  *
  * Container for the current bulk move state. Should be used with
  * ttm_lru_bulk_move_init() and ttm_bo_set_bulk_move().
+ * All BOs in a bulk_move structure need to share the same reservation object to
+ * ensure that the bulk as a whole is locked for eviction even if only one BO of
+ * the bulk is evicted.
  */
 struct ttm_lru_bulk_move {
 	struct ttm_lru_bulk_move_pos pos[TTM_NUM_MEM_TYPES][TTM_MAX_BO_PRIORITY];