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@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;
