Re: [PATCH v2 2/2] drm/ttm, drm/i915: Update ttm_move_memcpy for async use

[Christian König <christian.koenig@xxxxxxx>]

Am 13.08.21 um 16:43 schrieb Thomas Hellström:
> The buffer object argument to ttm_move_memcpy was only used to
> determine whether the destination memory should be cleared only
> or whether we should copy data. Replace it with a "clear" bool, and
> update the callers.
>
> The intention here is to be able to use ttm_move_memcpy() async under
> a dma-fence as a fallback if an accelerated blit fails in a security-
> critical path where data might leak if the blit is not properly
> performed. For that purpose the bo is an unsuitable argument since
> its relevant members might already have changed at call time.
>
> Finally, update the ttm_move_memcpy kerneldoc that seems to have
> ended up with a stale version.
>
> Cc: Christian König <christian.koenig@xxxxxxx>
> Signed-off-by: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
> Reviewed-by: Matthew Auld <matthew.auld@xxxxxxxxx>

Reviewed-by: Christian König <christian.koenig@xxxxxxx>

> ---
>   drivers/gpu/drm/i915/gem/i915_gem_ttm.c |  2 +-
>   drivers/gpu/drm/ttm/ttm_bo_util.c       | 20 ++++++++++----------
>   include/drm/ttm/ttm_bo_driver.h         |  2 +-
>   3 files changed, 12 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> index d07de18529ab..6995c66cbe21 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> @@ -518,7 +518,7 @@ static void __i915_ttm_move(struct ttm_buffer_object *bo, bool clear,
>   						 obj->ttm.cached_io_st,
>   						 src_reg->region.start);
>   
> -		ttm_move_memcpy(bo, dst_mem->num_pages, dst_iter, src_iter);
> +		ttm_move_memcpy(clear, dst_mem->num_pages, dst_iter, src_iter);
>   	}
>   }
>   
> diff --git a/drivers/gpu/drm/ttm/ttm_bo_util.c b/drivers/gpu/drm/ttm/ttm_bo_util.c
> index 763fa6f4e07d..5c20d0541cc3 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo_util.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo_util.c
> @@ -78,22 +78,21 @@ void ttm_mem_io_free(struct ttm_device *bdev,
>   
>   /**
>    * ttm_move_memcpy - Helper to perform a memcpy ttm move operation.
> - * @bo: The struct ttm_buffer_object.
> - * @new_mem: The struct ttm_resource we're moving to (copy destination).
> - * @new_iter: A struct ttm_kmap_iter representing the destination resource.
> + * @clear: Whether to clear rather than copy.
> + * @num_pages: Number of pages of the operation.
> + * @dst_iter: A struct ttm_kmap_iter representing the destination resource.
>    * @src_iter: A struct ttm_kmap_iter representing the source resource.
>    *
>    * This function is intended to be able to move out async under a
>    * dma-fence if desired.
>    */
> -void ttm_move_memcpy(struct ttm_buffer_object *bo,
> +void ttm_move_memcpy(bool clear,
>   		     u32 num_pages,
>   		     struct ttm_kmap_iter *dst_iter,
>   		     struct ttm_kmap_iter *src_iter)
>   {
>   	const struct ttm_kmap_iter_ops *dst_ops = dst_iter->ops;
>   	const struct ttm_kmap_iter_ops *src_ops = src_iter->ops;
> -	struct ttm_tt *ttm = bo->ttm;
>   	struct dma_buf_map src_map, dst_map;
>   	pgoff_t i;
>   
> @@ -102,10 +101,7 @@ void ttm_move_memcpy(struct ttm_buffer_object *bo,
>   		return;
>   
>   	/* Don't move nonexistent data. Clear destination instead. */
> -	if (src_ops->maps_tt && (!ttm || !ttm_tt_is_populated(ttm))) {
> -		if (ttm && !(ttm->page_flags & TTM_PAGE_FLAG_ZERO_ALLOC))
> -			return;
> -
> +	if (clear) {
>   		for (i = 0; i < num_pages; ++i) {
>   			dst_ops->map_local(dst_iter, &dst_map, i);
>   			if (dst_map.is_iomem)
> @@ -149,6 +145,7 @@ int ttm_bo_move_memcpy(struct ttm_buffer_object *bo,
>   		struct ttm_kmap_iter_linear_io io;
>   	} _dst_iter, _src_iter;
>   	struct ttm_kmap_iter *dst_iter, *src_iter;
> +	bool clear;
>   	int ret = 0;
>   
>   	if (ttm && ((ttm->page_flags & TTM_PAGE_FLAG_SWAPPED) ||
> @@ -172,7 +169,10 @@ int ttm_bo_move_memcpy(struct ttm_buffer_object *bo,
>   		goto out_src_iter;
>   	}
>   
> -	ttm_move_memcpy(bo, dst_mem->num_pages, dst_iter, src_iter);
> +	clear = src_iter->ops->maps_tt && (!ttm || !ttm_tt_is_populated(ttm));
> +	if (!(clear && ttm && !(ttm->page_flags & TTM_PAGE_FLAG_ZERO_ALLOC)))
> +		ttm_move_memcpy(clear, dst_mem->num_pages, dst_iter, src_iter);
> +
>   	src_copy = *src_mem;
>   	ttm_bo_move_sync_cleanup(bo, dst_mem);
>   
> diff --git a/include/drm/ttm/ttm_bo_driver.h b/include/drm/ttm/ttm_bo_driver.h
> index 68d6069572aa..5f087575194b 100644
> --- a/include/drm/ttm/ttm_bo_driver.h
> +++ b/include/drm/ttm/ttm_bo_driver.h
> @@ -322,7 +322,7 @@ int ttm_bo_tt_bind(struct ttm_buffer_object *bo, struct ttm_resource *mem);
>    */
>   void ttm_bo_tt_destroy(struct ttm_buffer_object *bo);
>   
> -void ttm_move_memcpy(struct ttm_buffer_object *bo,
> +void ttm_move_memcpy(bool clear,
>   		     u32 num_pages,
>   		     struct ttm_kmap_iter *dst_iter,
>   		     struct ttm_kmap_iter *src_iter);