On Mon, Jul 18, 2022 at 8:05 PM Eugenio Pérez <epere...@redhat.com> wrote:
>
> The SVQ vring used idx usually match with the guest visible one, as long
> as all the guest buffers (GPA) maps to exactly one buffer within qemu's
> VA. However, as we can see in virtqueue_map_desc, a single guest buffer
> could map to many buffers in SVQ vring.
>
> Also, its also a mistake to rewind them at the source of migration.
> Since VirtQueue is able to migrate the inflight descriptors, its
> responsability of the destination to perform the rewind just in case it
> cannot report the inflight descriptors to the device.
>
> This makes easier to migrate between backends or to recover them in
> vhost devices that support set in flight descriptors.
>
> Fixes: 6d0b22266633 ("vdpa: Adapt vhost_vdpa_get_vring_base to SVQ")
> Signed-off-by: Eugenio Pérez <epere...@redhat.com>
Acked-by: Jason Wang <jasow...@redhat.com>
>
> --
> v2: Squash both fixes in one.
> ---
> hw/virtio/vhost-vdpa.c | 24 ++++++++++++------------
> 1 file changed, 12 insertions(+), 12 deletions(-)
>
> diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c
> index 795ed5a049..4458c8d23e 100644
> --- a/hw/virtio/vhost-vdpa.c
> +++ b/hw/virtio/vhost-vdpa.c
> @@ -1178,7 +1178,18 @@ 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
> @@ -1194,21 +1205,10 @@ static int vhost_vdpa_get_vring_base(struct vhost_dev
> *dev,
> struct vhost_vring_state *ring)
> {
> struct vhost_vdpa *v = dev->opaque;
> - int vdpa_idx = ring->index - dev->vq_index;
> int ret;
>
> if (v->shadow_vqs_enabled) {
> - VhostShadowVirtqueue *svq = g_ptr_array_index(v->shadow_vqs,
> vdpa_idx);
> -
> - /*
> - * Setting base as last used idx, so destination will see as
> available
> - * all the entries that the device did not use, including the
> in-flight
> - * processing ones.
> - *
> - * TODO: This is ok for networking, but other kinds of devices might
> - * have problems with these retransmissions.
> - */
> - ring->num = svq->last_used_idx;
> + ring->num = virtio_queue_get_last_avail_idx(dev->vdev, ring->index);
> return 0;
> }
>
> --
> 2.31.1
>
