Re: [PATCH] virtio-net: fix qemu set used ring flag even vhost started

[Michael Tokarev]

02.04.2024 07:51, Yajun Wu:

When vhost-user or vhost-kernel is handling virtio net datapath, qemu
should not touch used ring.

But with vhost-user socket reconnect scenario, in a very rare case (has
pending kick event). VRING_USED_F_NO_NOTIFY is set by qemu in
following code path:

...

This issue causes guest kernel stop kicking device and traffic stop.

Add vhost_started check in virtio_net_handle_tx_bh to fix this wrong
VRING_USED_F_NO_NOTIFY set.

This seems to be qemu-stable material, even if the case when the issue
happens is "very rare", -- is it not?

Thanks,

/mjt

Signed-off-by: Yajun Wu <yaj...@nvidia.com>
Reviewed-by: Jiri Pirko <j...@nvidia.com>
---
  hw/net/virtio-net.c | 4 ++++
  1 file changed, 4 insertions(+)

diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index a6ff000cd9..8035e01fdf 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -2865,6 +2865,10 @@ static void virtio_net_handle_tx_bh(VirtIODevice *vdev, 
VirtQueue *vq)
      VirtIONet *n = VIRTIO_NET(vdev);
      VirtIONetQueue *q = &n->vqs[vq2q(virtio_get_queue_index(vq))];

+ if (n->vhost_started) {

+        return;
+    }
+
      if (unlikely((n->status & VIRTIO_NET_S_LINK_UP) == 0)) {
          virtio_net_drop_tx_queue_data(vdev, vq);
          return;