Messages in this thread | | | Subject | Re: [PATCH 1/3] virtio_ring: always warn when descriptor chain exceeds queue size | From | Jason Wang <> | Date | Tue, 23 Mar 2021 10:38:41 +0800 |
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在 2021/3/22 下午4:17, Michael S. Tsirkin 写道: > 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?
Will do.
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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