[PATCH v4 08/15] vdpa: rewind at get_base, not set_base

["Eugenio Pérez" <eperezma@redhat.com>]

At this moment it is only possible to migrate to a vdpa device running
with x-svq=on. As a protective measure, the rewind of the inflight
descriptors was done at the destination. That way if the source sent a
virtqueue with inuse descriptors they are always discarded.

Since this series allows to migrate also to passthrough devices with no
SVQ, the right thing to do is to rewind at the source so the base of
vrings are correct.

Support for inflight descriptors may be added in the future.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
---
v4:
* Use virtqueue_unpop at vhost_svq_stop instead of rewinding at
  vhost_vdpa_get_vring_base.
---
 hw/virtio/vhost-shadow-virtqueue.c |  8 ++++++--
 hw/virtio/vhost-vdpa.c             | 11 -----------
 2 files changed, 6 insertions(+), 13 deletions(-)

diff --git a/hw/virtio/vhost-shadow-virtqueue.c b/hw/virtio/vhost-shadow-virtqueue.c
index 4307296358..523b379439 100644
--- a/hw/virtio/vhost-shadow-virtqueue.c
+++ b/hw/virtio/vhost-shadow-virtqueue.c
@@ -694,13 +694,17 @@ void vhost_svq_stop(VhostShadowVirtqueue *svq)
         g_autofree VirtQueueElement *elem = NULL;
         elem = g_steal_pointer(&svq->desc_state[i].elem);
         if (elem) {
-            virtqueue_detach_element(svq->vq, elem, 0);
+            /*
+             * TODO: This is ok for networking, but other kinds of devices
+             * might have problems with just unpop these.
+             */
+            virtqueue_unpop(svq->vq, elem, 0);
         }
     }
 
     next_avail_elem = g_steal_pointer(&svq->next_guest_avail_elem);
     if (next_avail_elem) {
-        virtqueue_detach_element(svq->vq, next_avail_elem, 0);
+        virtqueue_unpop(svq->vq, next_avail_elem, 0);
     }
     svq->vq = NULL;
     g_free(svq->desc_next);
diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c
index f542960a64..71e3dc21fe 100644
--- a/hw/virtio/vhost-vdpa.c
+++ b/hw/virtio/vhost-vdpa.c
@@ -1218,18 +1218,7 @@ static int vhost_vdpa_set_vring_base(struct vhost_dev *dev,
                                        struct vhost_vring_state *ring)
 {
     struct vhost_vdpa *v = dev->opaque;
-    VirtQueue *vq = virtio_get_queue(dev->vdev, ring->index);
 
-    /*
-     * vhost-vdpa devices does not support in-flight requests. Set all of them
-     * as available.
-     *
-     * TODO: This is ok for networking, but other kinds of devices might
-     * have problems with these retransmissions.
-     */
-    while (virtqueue_rewind(vq, 1)) {
-        continue;
-    }
     if (v->shadow_vqs_enabled) {
         /*
          * Device vring base was set at device start. SVQ base is handled by
-- 
2.31.1