virtio-pci: fix level interrupts

mask notifiers are never called without msix,
so devices with backend masking like vhost don't work.
Call mask notifiers explicitly at
startup/cleanup to make it work.
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>
Tested-by: NAlexander Graf <agraf@suse.de>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

hw/virtio/virtio-pci.c

@@ -744,6 +744,7 @@ static int virtio_pci_set_guest_notifier(DeviceState *d, int n, bool assign,
                                          bool with_irqfd)
 {
     VirtIOPCIProxy *proxy = to_virtio_pci_proxy(d);
+    VirtioDeviceClass *vdc = VIRTIO_DEVICE_GET_CLASS(proxy->vdev);
     VirtQueue *vq = virtio_get_queue(proxy->vdev, n);
     EventNotifier *notifier = virtio_queue_get_guest_notifier(vq);
 
@@ -758,6 +759,10 @@ static int virtio_pci_set_guest_notifier(DeviceState *d, int n, bool assign,
         event_notifier_cleanup(notifier);
     }
 
+    if (!msix_enabled(&proxy->pci_dev) && vdc->guest_notifier_mask) {
+        vdc->guest_notifier_mask(proxy->vdev, n, !assign);
+    }
+
     return 0;
 }