Re: [PATCH v4 4/5] accel/amdxdna: refuse to flush an imported BO

[Lizhi Hou <lizhi.hou@amd.com>]

On 8/17/26 16:07, Taimuraz Kaitmazov wrote:
> SYNC_BO clflushes an imported BO's scatterlist. An importer may not do
> that: the memory belongs to the exporter, and dma-buf gives the importer
> no interface to ask for maintenance on it. Refuse the request instead.
>
> is_import_bo() is (obj)->attach, which covers more than foreign buffers.
> A userptr BO arrives through a ubuf, and on a carveout device every share
> BO and the device heap arrive through a cbuf, so SYNC_BO answers
> -EOPNOTSUPP for those too, including the AMDXDNA_BO_DEV path that flushes
> through its heap.
>
> Only the ubuf case gives up maintenance it was getting: on a 64 MiB
> userptr BO a 4 KiB sync and a full sync both cost 659 us, this arm having
> ignored the range. amdxdna_cbuf_map() fills in only the DMA address and
> length, so drm_clflush_sg() already walks zero pages on carveout memory.
> Userspace maintains these through the mapping it already holds, as XRT's
> buffer::sync() does unless it is told to sync through the driver.
>
> Suggested-by: Lizhi Hou <lizhi.hou@amd.com>
> Signed-off-by: Taimuraz Kaitmazov <taimuraz@kaitmazov.com>
> ---
>   drivers/accel/amdxdna/amdxdna_gem.c | 7 ++++---
>   1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/accel/amdxdna/amdxdna_gem.c b/drivers/accel/amdxdna/amdxdna_gem.c
> index 4f38f985c74e..a713a9982d34 100644
> --- a/drivers/accel/amdxdna/amdxdna_gem.c
> +++ b/drivers/accel/amdxdna/amdxdna_gem.c
> @@ -1224,6 +1224,9 @@ static int amdxdna_flush_bo(struct amdxdna_gem_obj *abo, u64 offset, u64 size)
>   {
>   	u64 end;
>   
> +	if (is_import_bo(abo))
> +		return -EOPNOTSUPP;
> +
>   	if (offset >= abo->mem.size)
>   		return -EINVAL;
>   
> @@ -1234,9 +1237,7 @@ static int amdxdna_flush_bo(struct amdxdna_gem_obj *abo, u64 offset, u64 size)
>   	if (!size)
>   		return 0;
>   
> -	if (is_import_bo(abo))
> -		drm_clflush_sg(abo->base.sgt);
> -	else if (amdxdna_gem_vmap(abo))
> +	if (amdxdna_gem_vmap(abo))
Reviewed-by: Lizhi Hou <lizhi.hou@amd.com>
>   		drm_clflush_virt_range(amdxdna_gem_vmap(abo) + offset, size);
>   	else if (abo->base.pages)
>   		drm_clflush_pages(abo->base.pages, abo->mem.size >> PAGE_SHIFT);