Re: [PATCH v3] virtio_ring: use shadow flags when detaching split descriptors

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Oct 08, 2026 at 02:04:23PM +0900, sung byeongchan wrote:
> From: sungbyeongchan <tjdqudcks0424@naver.com>
> 
> Split virtqueues save descriptor flags and next indexes in desc_extra
> before publishing descriptors to the device. The detach path uses the
> shadow next index, but decides whether to continue by rereading the NEXT
> flag from the shared descriptor.
> 
> Use the shadow flags for the continuation decision as well. This keeps
> all detach metadata in the same driver-owned snapshot and avoids an
> unnecessary shared-ring read.
> 
> Fixes: 72b5e8958738 ("virtio-ring: store DMA metadata in desc_extra for split virtqueue")
> Acked-by: Michael S. Tsirkin <mst@redhat.com>
> Assisted-by: LLM
> Signed-off-by: sungbyeongchan <tjdqudcks0424@naver.com>
> ---

Thanks, will apply! Can you pls confirm sungbyeongchan without space is your
preferred form to be called, and not a mistake? 


> Changes in v3:
> - Restore a concise commit message explaining the mixed shared/shadow
>   metadata problem. The v2 response had removed the whole description.
> - Keep Michael's Acked-by.
> - No code changes.
> 
> Changes in v2:
> - Drop the two paragraphs Michael identified as unnecessary.
> - Add Michael's Acked-by.
> 
>  drivers/virtio/virtio_ring.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index db678f5a80e03..b4cb433df1dec 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -905,7 +905,6 @@ static unsigned detach_buf_split_in_order(struct vring_virtqueue *vq,
>  {
>  	struct vring_desc_extra *extra;
>  	unsigned int i;
> -	__virtio16 nextflag = cpu_to_virtio16(vq->vq.vdev, VRING_DESC_F_NEXT);
>  
>  	/* Clear data ptr. */
>  	vq->split.desc_state[head].data = NULL;
> @@ -915,7 +914,7 @@ static unsigned detach_buf_split_in_order(struct vring_virtqueue *vq,
>  	/* Put back on free list: unmap first-level descriptors and find end */
>  	i = head;
>  
> -	while (vq->split.vring.desc[i].flags & nextflag) {
> +	while (extra[i].flags & VRING_DESC_F_NEXT) {
>  		i = vring_unmap_one_split(vq, &extra[i]);
>  		vq->vq.num_free++;
>  	}
> base-commit: 0c2669a9f4a1d607e7591ae50ccf3c432a0aff08
> -- 
> 2.43.0