[PATCH 3/4] drm/vmwgfx: handle NULL bo->resource in move callback

[Matthew Auld]

The ttm bo now initially has NULL bo->resource, and leaves the driver
the handle that. However it looks like we forgot to handle that for
vmwgfx.  It looks like this will just null-ptr-deref in vmw_move(), if
bo->resource is NULL.

Fix this by calling move_null() if the new resource is TTM_PL_SYSTEM,
otherwise do the multi-hop sequence to ensure can safely call into
ttm_bo_move_memcpy(), since it might also need to clear the memory.
This should give the same behaviour as before.

Fixes: 180253782038 ("drm/ttm: stop allocating dummy resources during BO creation")
Signed-off-by: Matthew Auld <matthew.auld at intel.com>
Cc: Christian König <christian.koenig at amd.com>
---
 drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c b/drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c
index 856a352a72a6..c598c5a9fe2c 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c
@@ -596,10 +596,23 @@ static int vmw_move(struct ttm_buffer_object *bo,
 		    struct ttm_resource *new_mem,
 		    struct ttm_place *hop)
 {
-	struct ttm_resource_manager *old_man = ttm_manager_type(bo->bdev, bo->resource->mem_type);
+	struct ttm_resource_manager *old_man;
 	struct ttm_resource_manager *new_man = ttm_manager_type(bo->bdev, new_mem->mem_type);
 	int ret;
 
+	if (!bo->resource) {
+		if (new_mem->mem_type != TTM_PL_SYSTEM) {
+			hop->mem_type = TTM_PL_SYSTEM;
+			hop->flags = TTM_PL_FLAG_TEMPORARY;
+			return -EMULTIHOP;
+		}
+
+		ttm_bo_move_null(bo, new_mem);
+		return 0;
+	}
+
+	old_man = ttm_manager_type(bo->bdev, bo->resource->mem_type);
+
 	if (new_man->use_tt && !vmw_memtype_is_system(new_mem->mem_type)) {
 		ret = vmw_ttm_bind(bo->bdev, bo->ttm, new_mem);
 		if (ret)
-- 
2.39.1