[RFC v2 06/13] vhost: delay set_vring_ready after DRIVER_OK

[Eugenio Pérez]

To restore the device at the destination of a live migration we send the
commands through control virtqueue. For a device to read CVQ it must
have received the DRIVER_OK status bit.

However this opens a window where the device could start receiving
packets in rx queue 0 before it receives the RSS configuration. To avoid
that, we will not send vring_enable until all configuration is used by
the device.

As a first step, run vhost_set_vring_ready for all vhost_net backend after
all of them are started (with DRIVER_OK). This code should not affect
vdpa.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
---
 hw/net/vhost_net.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/hw/net/vhost_net.c b/hw/net/vhost_net.c
index c4eecc6f36..3900599465 100644
--- a/hw/net/vhost_net.c
+++ b/hw/net/vhost_net.c
@@ -399,6 +399,18 @@ int vhost_net_start(VirtIODevice *dev, NetClientState *ncs,
         } else {
             peer = qemu_get_peer(ncs, n->max_queue_pairs);
         }
+        r = vhost_net_start_one(get_vhost_net(peer), dev);
+        if (r < 0) {
+            goto err_start;
+        }
+    }
+
+    for (int j = 0; j < nvhosts; j++) {
+        if (j < data_queue_pairs) {
+            peer = qemu_get_peer(ncs, j);
+        } else {
+            peer = qemu_get_peer(ncs, n->max_queue_pairs);
+        }
 
         if (peer->vring_enable) {
             /* restore vring enable state */
@@ -408,11 +420,6 @@ int vhost_net_start(VirtIODevice *dev, NetClientState *ncs,
                 goto err_start;
             }
         }
-
-        r = vhost_net_start_one(get_vhost_net(peer), dev);
-        if (r < 0) {
-            goto err_start;
-        }
     }
 
     return 0;
-- 
2.31.1