[RFC v2 13/13] vhost: Use VRING_AVAIL_F_NO_INTERRUPT at device call on shadow virtqueue

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

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
---
 hw/virtio/vhost-shadow-virtqueue.c | 28 +++++++++++++++++++++++++++-
 1 file changed, 27 insertions(+), 1 deletion(-)

diff --git a/hw/virtio/vhost-shadow-virtqueue.c b/hw/virtio/vhost-shadow-virtqueue.c
index 7df98fc43f..e3879a4622 100644
--- a/hw/virtio/vhost-shadow-virtqueue.c
+++ b/hw/virtio/vhost-shadow-virtqueue.c
@@ -71,10 +71,35 @@ typedef struct VhostShadowVirtqueue {
     /* Next head to consume from device */
     uint16_t used_idx;
 
+    /* Cache for the exposed notification flag */
+    bool notification;
+
     /* Descriptors copied from guest */
     vring_desc_t descs[];
 } VhostShadowVirtqueue;
 
+static void vhost_shadow_vq_set_notification(VhostShadowVirtqueue *svq,
+                                             bool enable)
+{
+    uint16_t notification_flag;
+
+    if (svq->notification == enable) {
+        return;
+    }
+
+    notification_flag = virtio_tswap16(svq->vdev, VRING_AVAIL_F_NO_INTERRUPT);
+
+    svq->notification = enable;
+    if (enable) {
+        svq->vring.avail->flags &= ~notification_flag;
+    } else {
+        svq->vring.avail->flags |= notification_flag;
+    }
+
+    /* Make sure device reads our flag */
+    smp_mb();
+}
+
 static void vhost_vring_write_descs(VhostShadowVirtqueue *svq,
                                     const struct iovec *iovec,
                                     size_t num, bool more_descs, bool write)
@@ -251,7 +276,7 @@ static void vhost_shadow_vq_handle_call_no_test(EventNotifier *n)
     do {
         unsigned i = 0;
 
-        /* TODO: Use VRING_AVAIL_F_NO_INTERRUPT */
+        vhost_shadow_vq_set_notification(svq, false);
         while (true) {
             g_autofree VirtQueueElement *elem = vhost_shadow_vq_get_buf(svq);
             if (!elem) {
@@ -269,6 +294,7 @@ static void vhost_shadow_vq_handle_call_no_test(EventNotifier *n)
             svq->masked_notifier.signaled = true;
             event_notifier_set(svq->masked_notifier.n);
         }
+        vhost_shadow_vq_set_notification(svq, true);
     } while (vhost_shadow_vq_more_used(svq));
 
     if (masked_notifier) {
-- 
2.27.0