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

[sashiko-bot@kernel.org]

> 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.
> 
> A device can change the flag after publication and make
> detach_buf_split_in_order() detach an adjacent active descriptor. This
> overcounts num_free and may put a descriptor on the free list twice.
> 
> 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.
> 
> A VDUSE/virtio-vdpa test which changed NEXT after publication made six
> valid completions return seven descriptors, with one descriptor ID
> duplicated on refill. With this change, the same test returned six
> unique descriptors, while the unmodified control remained unchanged.
> 
> Fixes: 72b5e8958738 ("virtio-ring: store DMA metadata in desc_extra for split virtqueue")
> Assisted-by: LLM
> Signed-off-by: sungbyeongchan <tjdqudcks0424@naver.com>

Sashiko has reviewed this patch and found no issues. It looks great!

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Sashiko AI review · https://sashiko.dev/#/patchset/20261006100400.842345-1-tjdqudcks0424@naver.com?part=1