From: Bin Wu <wu.wubin@huawei.com>
Date: Fri, 31 Oct 2014 00:40:16 +0000 (+0000)
Subject: hw/virtio/vring/event_idx: fix the vring_avail_event error
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=a3614c65cfc3ba2958b69befdc156101953f8a8c;p=qemu.git

hw/virtio/vring/event_idx: fix the vring_avail_event error

The event idx in virtio is an effective way to reduce the number of
interrupts and exits of the guest. When the guest puts an request
into the virtio ring, it doesn't exit immediately to inform the
backend. Instead, the guest checks the "avail" event idx to determine
the notification.

In virtqueue_pop, when a request is poped, the current avail event
idx should be set to the number of vq->last_avail_idx.

Signed-off-by: Bin Wu <wu.wubin@huawei.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
---

diff --git a/hw/virtio/dataplane/vring.c b/hw/virtio/dataplane/vring.c
index 372706a234..61f6d83686 100644
--- a/hw/virtio/dataplane/vring.c
+++ b/hw/virtio/dataplane/vring.c
@@ -352,10 +352,6 @@ int vring_pop(VirtIODevice *vdev, Vring *vring,
         goto out;
     }
 
-    if (vdev->guest_features & (1 << VIRTIO_RING_F_EVENT_IDX)) {
-        vring_avail_event(&vring->vr) = vring->vr.avail->idx;
-    }
-
     i = head;
     do {
         if (unlikely(i >= num)) {
@@ -392,6 +388,10 @@ int vring_pop(VirtIODevice *vdev, Vring *vring,
 
     /* On success, increment avail index. */
     vring->last_avail_idx++;
+    if (vdev->guest_features & (1 << VIRTIO_RING_F_EVENT_IDX)) {
+        vring_avail_event(&vring->vr) = vring->last_avail_idx;
+    }
+
     return head;
 
 out:
diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 2c236bf271..013979a6b8 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -469,7 +469,7 @@ int virtqueue_pop(VirtQueue *vq, VirtQueueElement *elem)
 
     i = head = virtqueue_get_head(vq, vq->last_avail_idx++);
     if (vdev->guest_features & (1 << VIRTIO_RING_F_EVENT_IDX)) {
-        vring_avail_event(vq, vring_avail_idx(vq));
+        vring_avail_event(vq, vq->last_avail_idx);
     }
 
     if (vring_desc_flags(vdev, desc_pa, i) & VRING_DESC_F_INDIRECT) {