On Mon, Mar 22, 2021 at 11:22:15AM +0800, Jason Wang wrote:
>
> 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
It would be quite strange for packed and split to differ here:
so for packed would you say there's no limit on # of descriptors at all?
I am guessing I just forgot to move this part from
the format specific to the common part of the spec.
This needs discussion in the TC mailing list - want to start a thread
there?
>
> >
> > Reported-by: Stefan Hajnoczi <stefanha@xxxxxxxxxx>
> > Signed-off-by: Connor Kuehl <ckuehl@xxxxxxxxxx>
> > ---
> > 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;
