libvhost-user: support resuming vq->last_avail_idx based on used_idx

This is the same workaround as commit 523b018dde3b765, which was lost
with libvhost-user transition in commit e10e798c85c2331.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/contrib/libvhost-user/libvhost-user.c b/contrib/libvhost-user/libvhost-user.c
index 35fa0c5e56..d27d6303db 100644
--- a/contrib/libvhost-user/libvhost-user.c
+++ b/contrib/libvhost-user/libvhost-user.c
@@ -521,6 +521,19 @@ vu_set_vring_addr_exec(VuDev *dev, VhostUserMsg *vmsg)
 
     vq->used_idx = vq->vring.used->idx;
 
+    if (vq->last_avail_idx != vq->used_idx) {
+        bool resume = dev->iface->queue_is_processed_in_order &&
+            dev->iface->queue_is_processed_in_order(dev, index);
+
+        DPRINT("Last avail index != used index: %u != %u%s\n",
+               vq->last_avail_idx, vq->used_idx,
+               resume ? ", resuming" : "");
+
+        if (resume) {
+            vq->shadow_avail_idx = vq->last_avail_idx = vq->used_idx;
+        }
+    }
+
     return false;
 }