Messages in this thread Patch in this message | | | Subject | Re: [PATCH 1/3] virtio_ring: always warn when descriptor chain exceeds queue size | From | Jason Wang <> | Date | Mon, 22 Mar 2021 11:22:15 +0800 |
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在 2021/3/18 下午9:52, Connor Kuehl 写道: > From section 2.6.5.3.1 (Driver Requirements: Indirect Descriptors) > of the virtio spec: > > "A driver MUST NOT create a descriptor chain longer than the Queue > Size of the device." > > This text suggests that the warning should trigger even if > indirect descriptors are in use.
So I think at least the commit log needs some tweak.
For split virtqueue. We had:
2.6.5.2 Driver Requirements: The Virtqueue Descriptor Table
Drivers MUST NOT add a descriptor chain longer than 2^32 bytes in total; this implies that loops in the descriptor chain are forbidden!
2.6.5.3.1 Driver Requirements: Indirect Descriptors
A driver MUST NOT create a descriptor chain longer than the Queue Size of the device.
If I understand the spec correctly, the check is only needed for a single indirect descriptor table?
For packed virtqueue. We had:
2.7.17 Driver Requirements: Scatter-Gather Support
A driver MUST NOT create a descriptor list longer than allowed by the device.
A driver MUST NOT create a descriptor list longer than the Queue Size.
2.7.19 Driver Requirements: Indirect Descriptors
A driver MUST NOT create a descriptor chain longer than allowed by the device.
So it looks to me the packed part is fine.
Note that if I understand the spec correctly 2.7.17 implies 2.7.19.
Thanks
> > Reported-by: Stefan Hajnoczi <stefanha@redhat.com> > Signed-off-by: Connor Kuehl <ckuehl@redhat.com> > --- > drivers/virtio/virtio_ring.c | 7 ++++--- > 1 file changed, 4 insertions(+), 3 deletions(-) > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > index 71e16b53e9c1..1bc290f9ba13 100644 > --- a/drivers/virtio/virtio_ring.c > +++ b/drivers/virtio/virtio_ring.c > @@ -444,11 +444,12 @@ static inline int virtqueue_add_split(struct virtqueue *_vq, > > head = vq->free_head; > > + WARN_ON_ONCE(total_sg > vq->split.vring.num); > + > if (virtqueue_use_indirect(_vq, total_sg)) > desc = alloc_indirect_split(_vq, total_sg, gfp); > else { > desc = NULL; > - WARN_ON_ONCE(total_sg > vq->split.vring.num && !vq->indirect); > } > > if (desc) { > @@ -1118,6 +1119,8 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq, > > BUG_ON(total_sg == 0); > > + WARN_ON_ONCE(total_sg > vq->packed.vring.num); > + > if (virtqueue_use_indirect(_vq, total_sg)) > return virtqueue_add_indirect_packed(vq, sgs, total_sg, > out_sgs, in_sgs, data, gfp); > @@ -1125,8 +1128,6 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq, > head = vq->packed.next_avail_idx; > avail_used_flags = vq->packed.avail_used_flags; > > - WARN_ON_ONCE(total_sg > vq->packed.vring.num && !vq->indirect); > - > desc = vq->packed.vring.desc; > i = head; > descs_used = total_sg;
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