[Stable-8.2.3 80/87] hw/net/virtio-net: fix qemu set used ring flag even vhost started

[Michael Tokarev]

From: Yajun Wu <yajunw@nvidia.com>

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:

        #0  virtio_queue_split_set_notification (vq=0x7ff5f4c920a8, enable=0) 
at ../hw/virtio/virtio.c:511
        #1  0x0000559d6dbf033b in virtio_queue_set_notification 
(vq=0x7ff5f4c920a8, enable=0) at ../hw/virtio/virtio.c:576
        #2  0x0000559d6dbbbdbc in virtio_net_handle_tx_bh (vdev=0x559d703a6aa0, 
vq=0x7ff5f4c920a8) at ../hw/net/virtio-net.c:2801
        #3  0x0000559d6dbf4791 in virtio_queue_notify_vq (vq=0x7ff5f4c920a8) at 
../hw/virtio/virtio.c:2248
        #4  0x0000559d6dbf79da in virtio_queue_host_notifier_read 
(n=0x7ff5f4c9211c) at ../hw/virtio/virtio.c:3525
        #5  0x0000559d6d9a5814 in virtio_bus_cleanup_host_notifier 
(bus=0x559d703a6a20, n=1) at ../hw/virtio/virtio-bus.c:321
        #6  0x0000559d6dbf83c9 in virtio_device_stop_ioeventfd_impl 
(vdev=0x559d703a6aa0) at ../hw/virtio/virtio.c:3774
        #7  0x0000559d6d9a55c8 in virtio_bus_stop_ioeventfd 
(bus=0x559d703a6a20) at ../hw/virtio/virtio-bus.c:259
        #8  0x0000559d6d9a53e8 in virtio_bus_grab_ioeventfd 
(bus=0x559d703a6a20) at ../hw/virtio/virtio-bus.c:199
        #9  0x0000559d6dbf841c in virtio_device_grab_ioeventfd 
(vdev=0x559d703a6aa0) at ../hw/virtio/virtio.c:3783
        #10 0x0000559d6d9bde18 in vhost_dev_enable_notifiers 
(hdev=0x559d707edd70, vdev=0x559d703a6aa0) at ../hw/virtio/vhost.c:1592
        #11 0x0000559d6d89a0b8 in vhost_net_start_one (net=0x559d707edd70, 
dev=0x559d703a6aa0) at ../hw/net/vhost_net.c:266
        #12 0x0000559d6d89a6df in vhost_net_start (dev=0x559d703a6aa0, 
ncs=0x559d7048d890, data_queue_pairs=31, cvq=0) at ../hw/net/vhost_net.c:412
        #13 0x0000559d6dbb5b89 in virtio_net_vhost_status (n=0x559d703a6aa0, 
status=15 '\017') at ../hw/net/virtio-net.c:311
        #14 0x0000559d6dbb5e34 in virtio_net_set_status (vdev=0x559d703a6aa0, 
status=15 '\017') at ../hw/net/virtio-net.c:392
        #15 0x0000559d6dbb60d8 in virtio_net_set_link_status 
(nc=0x559d7048d890) at ../hw/net/virtio-net.c:455
        #16 0x0000559d6da64863 in qmp_set_link (name=0x559d6f0b83d0 "hostnet1", 
up=true, errp=0x7ffdd76569f0) at ../net/net.c:1459
        #17 0x0000559d6da7226e in net_vhost_user_event (opaque=0x559d6f0b83d0, 
event=CHR_EVENT_OPENED) at ../net/vhost-user.c:301
        #18 0x0000559d6ddc7f63 in chr_be_event (s=0x559d6f2ffea0, 
event=CHR_EVENT_OPENED) at ../chardev/char.c:62
        #19 0x0000559d6ddc7fdc in qemu_chr_be_event (s=0x559d6f2ffea0, 
event=CHR_EVENT_OPENED) at ../chardev/char.c:82

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.

Signed-off-by: Yajun Wu <yajunw@nvidia.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Message-ID: <20240402045109.97729-1-yajunw@nvidia.com>
[PMD: Use unlikely()]
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
(cherry picked from commit 4c54f5bc8e1d38f15cc35b6a6932d8fbe219c692)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index a29c1fafd4..8451dbee41 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -2809,6 +2809,10 @@ 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 (unlikely(n->vhost_started)) {
+        return;
+    }
+
     if (unlikely((n->status & VIRTIO_NET_S_LINK_UP) == 0)) {
         virtio_net_drop_tx_queue_data(vdev, vq);
         return;
-- 
2.39.2