Re: [RFC PATCH v4 16/20] vhost: Check for device VRING_USED_F_NO_NOTIFY at shadow virtqueue kick

[Jason Wang]

在 2021/10/1 下午3:05, Eugenio Pérez 写道:

Signed-off-by: Eugenio Pérez <epere...@redhat.com>
---
  hw/virtio/vhost-shadow-virtqueue.c | 11 ++++++++++-
  1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/hw/virtio/vhost-shadow-virtqueue.c 
b/hw/virtio/vhost-shadow-virtqueue.c
index df7e6fa3ec..775f8d36a0 100644
--- a/hw/virtio/vhost-shadow-virtqueue.c
+++ b/hw/virtio/vhost-shadow-virtqueue.c
@@ -173,6 +173,15 @@ static void vhost_svq_add(VhostShadowVirtqueue *svq, 
VirtQueueElement *elem)
      svq->ring_id_maps[qemu_head] = elem;
  }

+static void vhost_svq_kick(VhostShadowVirtqueue *svq)

+{
+    /* Make sure we are reading updated device flag */

I guess this would be better:

        /* We need to expose available array entries before checking used
         * flags. */

(Borrowed from kernel codes).

Thanks

+    smp_mb();
+    if (!(svq->vring.used->flags & VRING_USED_F_NO_NOTIFY)) {
+        event_notifier_set(&svq->kick_notifier);
+    }
+}
+
  /* Handle guest->device notifications */
  static void vhost_handle_guest_kick(EventNotifier *n)
  {
@@ -197,7 +206,7 @@ static void vhost_handle_guest_kick(EventNotifier *n)
              }

vhost_svq_add(svq, elem);

-            event_notifier_set(&svq->kick_notifier);
+            vhost_svq_kick(svq);
          }

virtio_queue_set_notification(svq->vq, true);