drm/ttm: Handle in-memory region copies

Fix the case where the ttm pointer may be NULL causing
a NULL pointer dereference.
Signed-off-by: NJakob Bornecrantz <jakob@vmware.com>
Signed-off-by: NThomas Hellström <thellstrom@vmware.com>
Cc: stable@vger.kernel.org

drivers/gpu/drm/ttm/ttm_bo_util.c

@@ -348,7 +348,9 @@ int ttm_bo_move_memcpy(struct ttm_buffer_object *bo,
 	if (old_iomap == NULL && ttm == NULL)
 		goto out2;
 
-	if (ttm->state == tt_unpopulated) {
+	/* TTM might be null for moves within the same region.
+	 */
+	if (ttm && ttm->state == tt_unpopulated) {
 		ret = ttm->bdev->driver->ttm_tt_populate(ttm);
 		if (ret) {
 			/* if we fail here don't nuke the mm node