[RFC PATCH v5 02/26] vhost: Fix last queue index of devices with no cvq

[Eugenio Pérez]

The -1 assumes that all devices with no cvq have an spare vq allocated
for them, but with no offer of VIRTIO_NET_F_CTRL_VQ. This may not be the
case, and the device may have a pair number of queues.

To fix this, just resort to the lower even number of queues.

Fixes: 049eb15b5fc9 ("vhost: record the last virtqueue index for the virtio 
device")
Signed-off-by: Eugenio Pérez <epere...@redhat.com>
---
 hw/net/vhost_net.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/net/vhost_net.c b/hw/net/vhost_net.c
index 0d888f29a6..edf56a597f 100644
--- a/hw/net/vhost_net.c
+++ b/hw/net/vhost_net.c
@@ -330,7 +330,7 @@ int vhost_net_start(VirtIODevice *dev, NetClientState *ncs,
     NetClientState *peer;
 
     if (!cvq) {
-        last_index -= 1;
+        last_index &= ~1ULL;
     }
 
     if (!k->set_guest_notifiers) {
-- 
2.27.0