On 3/20/24 17:14, Michael S. Tsirkin wrote:
On Wed, Mar 20, 2024 at 03:24:16PM +1000, Gavin Shan wrote:
On 3/20/24 10:49, Michael S. Tsirkin wrote:>
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 6f7e5010a673..79456706d0bd 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -685,7 +685,8 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
/* Put entry in available array (but don't update avail->idx until they
* do sync). */
avail = vq->split.avail_idx_shadow & (vq->split.vring.num - 1);
- vq->split.vring.avail->ring[avail] = cpu_to_virtio16(_vq->vdev, head);
+ u16 headwithflag = head | (q->split.avail_idx_shadow & ~(vq->split.vring.num - 1));
+ vq->split.vring.avail->ring[avail] = cpu_to_virtio16(_vq->vdev, headwithflag);
/* Descriptors and available array need to be set before we expose the
* new available array entries. */
Ok, Michael. I continued with my debugging code. It still looks like a
hardware bug on NVidia's grace-hopper. I really think NVidia needs to be
involved for the discussion, as suggested by you.
Firstly, I bind the vhost process and vCPU thread to CPU#71 and CPU#70.
Note that I have only one vCPU in my configuration.
Secondly, the debugging code is enhanced so that the available head for
(last_avail_idx - 1) is read for twice and recorded. It means the available
head for one specific available index is read for twice. I do see the
available heads are different from the consecutive reads. More details
are shared as below.
From the guest side
===================
virtio_net virtio0: output.0:id 86 is not a head!
head to be released: 047 062 112
avail_idx:
000 49665
001 49666 <--
:
015 49664
avail_head:
000 062
001 047 <--
:
015 112
From the host side
==================
avail_idx
000 49663
001 49666 <---
:
avail_head
000 062 (062)
001 047 (047) <---
:
015 086 (112) // head 086 is returned from the first read,
// but head 112 is returned from the second read
vhost_get_vq_desc: Inconsistent head in two read (86 -> 112) for avail_idx 49664
Thanks,
Gavin
