Previous function misses the just picked avail buffer from the queue.
This way keeps blocking the used queue forever, but is cleaner to check
before calling to vhost_svq_get_buf.

Fixes: 100890f7cad50 ("vhost: Shadow virtqueue buffers forwarding")
Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
---
 hw/virtio/vhost-shadow-virtqueue.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/hw/virtio/vhost-shadow-virtqueue.c b/hw/virtio/vhost-shadow-virtqueue.c
index 56c96ebd13..9280285435 100644
--- a/hw/virtio/vhost-shadow-virtqueue.c
+++ b/hw/virtio/vhost-shadow-virtqueue.c
@@ -405,19 +405,21 @@ static void vhost_svq_flush(VhostShadowVirtqueue *svq,
         vhost_svq_disable_notification(svq);
         while (true) {
             uint32_t len;
-            g_autofree VirtQueueElement *elem = vhost_svq_get_buf(svq, &len);
-            if (!elem) {
-                break;
-            }
+            g_autofree VirtQueueElement *elem = NULL;
 
             if (unlikely(i >= svq->vring.num)) {
                 qemu_log_mask(LOG_GUEST_ERROR,
                          "More than %u used buffers obtained in a %u size SVQ",
                          i, svq->vring.num);
-                virtqueue_fill(vq, elem, len, i);
-                virtqueue_flush(vq, i);
+                virtqueue_flush(vq, svq->vring.num);
                 return;
             }
+
+            elem = vhost_svq_get_buf(svq, &len);
+            if (!elem) {
+                break;
+            }
+
             virtqueue_fill(vq, elem, len, i++);
         }
 
-- 
2.31.1

On Thu, Jul 7, 2022 at 2:40 AM Eugenio Pérez <eperezma@redhat.com> wrote:
>
> Previous function misses the just picked avail buffer from the queue.
> This way keeps blocking the used queue forever, but is cleaner to check
> before calling to vhost_svq_get_buf.
>
> Fixes: 100890f7cad50 ("vhost: Shadow virtqueue buffers forwarding")
> Signed-off-by: Eugenio Pérez <eperezma@redhat.com>

Acked-by: Jason Wang <jasowang@redhat.com>

> ---
>  hw/virtio/vhost-shadow-virtqueue.c | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/hw/virtio/vhost-shadow-virtqueue.c b/hw/virtio/vhost-shadow-virtqueue.c
> index 56c96ebd13..9280285435 100644
> --- a/hw/virtio/vhost-shadow-virtqueue.c
> +++ b/hw/virtio/vhost-shadow-virtqueue.c
> @@ -405,19 +405,21 @@ static void vhost_svq_flush(VhostShadowVirtqueue *svq,
>          vhost_svq_disable_notification(svq);
>          while (true) {
>              uint32_t len;
> -            g_autofree VirtQueueElement *elem = vhost_svq_get_buf(svq, &len);
> -            if (!elem) {
> -                break;
> -            }
> +            g_autofree VirtQueueElement *elem = NULL;
>
>              if (unlikely(i >= svq->vring.num)) {
>                  qemu_log_mask(LOG_GUEST_ERROR,
>                           "More than %u used buffers obtained in a %u size SVQ",
>                           i, svq->vring.num);
> -                virtqueue_fill(vq, elem, len, i);
> -                virtqueue_flush(vq, i);
> +                virtqueue_flush(vq, svq->vring.num);
>                  return;
>              }
> +
> +            elem = vhost_svq_get_buf(svq, &len);
> +            if (!elem) {
> +                break;
> +            }
> +
>              virtqueue_fill(vq, elem, len, i++);
>          }
>
> --
> 2.31.1
>