vhost: Fix device's used descriptor dequeue

Only the first one of them were properly enqueued back.

Fixes: 100890f7ca ("vhost: Shadow virtqueue buffers forwarding")

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
Message-Id: <20220512175747.142058-3-eperezma@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

diff --git a/hw/virtio/vhost-shadow-virtqueue.c b/hw/virtio/vhost-shadow-virtqueue.c
index 1d6552b..a8376ef 100644 (file)
--- a/hw/virtio/vhost-shadow-virtqueue.c
+++ b/hw/virtio/vhost-shadow-virtqueue.c
@@ -334,12 +334,22 @@ static void vhost_svq_disable_notification(VhostShadowVirtqueue *svq)
     svq->vring.avail->flags |= cpu_to_le16(VRING_AVAIL_F_NO_INTERRUPT);
 }
 
+static uint16_t vhost_svq_last_desc_of_chain(const VhostShadowVirtqueue *svq,
+                                             uint16_t num, uint16_t i)
+{
+    for (uint16_t j = 0; j < (num - 1); ++j) {
+        i = le16_to_cpu(svq->desc_next[i]);
+    }
+
+    return i;
+}
+
 static VirtQueueElement *vhost_svq_get_buf(VhostShadowVirtqueue *svq,
                                            uint32_t *len)
 {
     const vring_used_t *used = svq->vring.used;
     vring_used_elem_t used_elem;
-    uint16_t last_used;
+    uint16_t last_used, last_used_chain, num;
 
     if (!vhost_svq_more_used(svq)) {
         return NULL;
@@ -365,7 +375,10 @@ static VirtQueueElement *vhost_svq_get_buf(VhostShadowVirtqueue *svq,
         return NULL;
     }
 
-    svq->desc_next[used_elem.id] = svq->free_head;
+    num = svq->ring_id_maps[used_elem.id]->in_num +
+          svq->ring_id_maps[used_elem.id]->out_num;
+    last_used_chain = vhost_svq_last_desc_of_chain(svq, num, used_elem.id);
+    svq->desc_next[last_used_chain] = svq->free_head;
     svq->free_head = used_elem.id;
 
     *len = used_elem.len;