vhost: toggle device callbacks using used event idx

Actually use the new field of the used ring and tell the device if SVQ
wants to be notified.

The code is not reachable at the moment.

Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>

diff --git a/hw/virtio/vhost-shadow-virtqueue.c b/hw/virtio/vhost-shadow-virtqueue.c
index a518f8477244c99fbd57325109ed8b9443455283..f5c0fad3fc47094069ed45f37d9052c44dd18ea7 100644 (file)
--- a/hw/virtio/vhost-shadow-virtqueue.c
+++ b/hw/virtio/vhost-shadow-virtqueue.c
@@ -369,15 +369,27 @@ static bool vhost_svq_more_used(VhostShadowVirtqueue *svq)
  */
 static bool vhost_svq_enable_notification(VhostShadowVirtqueue *svq)
 {
-    svq->vring.avail->flags &= ~cpu_to_le16(VRING_AVAIL_F_NO_INTERRUPT);
-    /* Make sure the flag is written before the read of used_idx */
+    if (virtio_vdev_has_feature(svq->vdev, VIRTIO_RING_F_EVENT_IDX)) {
+        uint16_t *used_event = (uint16_t *)&svq->vring.avail->ring[svq->vring.num];
+        *used_event = svq->shadow_used_idx;
+    } else {
+        svq->vring.avail->flags &= ~cpu_to_le16(VRING_AVAIL_F_NO_INTERRUPT);
+    }
+
+    /* Make sure the event is enabled before the read of used_idx */
     smp_mb();
     return !vhost_svq_more_used(svq);
 }
 
 static void vhost_svq_disable_notification(VhostShadowVirtqueue *svq)
 {
-    svq->vring.avail->flags |= cpu_to_le16(VRING_AVAIL_F_NO_INTERRUPT);
+    /*
+     * No need to disable notification in the event idx case, since used event
+     * index is already an index too far away.
+     */
+    if (!virtio_vdev_has_feature(svq->vdev, VIRTIO_RING_F_EVENT_IDX)) {
+        svq->vring.avail->flags |= cpu_to_le16(VRING_AVAIL_F_NO_INTERRUPT);
+    }
 }
 
 static uint16_t vhost_svq_last_desc_of_chain(const VhostShadowVirtqueue *svq,