[PATCH v3 2/2] vhost: Fix last vq queue index of devices with no cvq

["Eugenio Pérez" <eperezma@redhat.com>]

The -1 assumes that last index counts all vhost device models as having
two queues, but they count only the ones that models the data queues.

Because of that, the right change in last_index is to actually add the
cvq, not to remove the missing one.

This is not a problem to vhost-net, but it is to vhost-vdpa, which
device model trust to reach the last index to finish starting the
device.

Tested with vp_vdpa with host's vhost=on and vhost=off, with ctrl_vq=on
and ctrl_vq=off.

Fixes: 049eb15b5fc9 ("vhost: record the last virtqueue index for the virtio device")
Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
---
 hw/net/vhost_net.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/hw/net/vhost_net.c b/hw/net/vhost_net.c
index 081946dc93..fe2b8a2b83 100644
--- a/hw/net/vhost_net.c
+++ b/hw/net/vhost_net.c
@@ -329,8 +329,8 @@ int vhost_net_start(VirtIODevice *dev, NetClientState *ncs,
     int r, e, i, last_index = data_queue_pairs * 2;
     NetClientState *peer;
 
-    if (!cvq) {
-        last_index -= 1;
+    if (cvq) {
+        last_index += 1;
     }
 
     if (!k->set_guest_notifiers) {
-- 
2.27.0