[PATCH 12/12] vdpa: fix network breakage after cancelling migration

[Si-Wei Liu <si-wei.liu@oracle.com>]

Fix an issue where cancellation of ongoing migration ends up
with no network connectivity.

When canceling migration, SVQ will be switched back to the
passthrough mode, but the right call fd is not programed to
the device and the svq's own call fd is still used. At the
point of this transitioning period, the shadow_vqs_enabled
hadn't been set back to false yet, causing the installation
of call fd inadvertently bypassed.

Fixes: a8ac88585da1 ("vhost: Add Shadow VirtQueue call forwarding capabilities")
Cc: Eugenio Pérez <eperezma@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Si-Wei Liu <si-wei.liu@oracle.com>
---
 hw/virtio/vhost-vdpa.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c
index 004110f..dfeca8b 100644
--- a/hw/virtio/vhost-vdpa.c
+++ b/hw/virtio/vhost-vdpa.c
@@ -1468,7 +1468,15 @@ static int vhost_vdpa_set_vring_call(struct vhost_dev *dev,
 
     /* Remember last call fd because we can switch to SVQ anytime. */
     vhost_svq_set_svq_call_fd(svq, file->fd);
-    if (v->shadow_vqs_enabled) {
+    /*
+     * When SVQ is transitioning to off, shadow_vqs_enabled has
+     * not been set back to false yet, but the underlying call fd
+     * will have to switch back to the guest notifier to signal the
+     * passthrough virtqueues. In other situations, SVQ's own call
+     * fd shall be used to signal the device model.
+     */
+    if (v->shadow_vqs_enabled &&
+        v->shared->svq_switching != SVQ_TSTATE_DISABLING) {
         return 0;
     }
 
-- 
1.8.3.1