Re: [RFC v2 04/13] vdpa: rewind at get_base, not set_base

[Jason Wang]

On Fri, Jan 13, 2023 at 1:24 AM Eugenio Pérez <eperezma@redhat.com> wrote:
>
> 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 base of vrings
> are correct.
>
> Support for inflight descriptors may be added in the future.
>
> Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> ---
>  include/hw/virtio/vhost-backend.h |  4 +++
>  hw/virtio/vhost-vdpa.c            | 46 +++++++++++++++++++------------
>  hw/virtio/vhost.c                 |  3 ++
>  3 files changed, 36 insertions(+), 17 deletions(-)
>
> diff --git a/include/hw/virtio/vhost-backend.h 
> b/include/hw/virtio/vhost-backend.h
> index c5ab49051e..ec3fbae58d 100644
> --- a/include/hw/virtio/vhost-backend.h
> +++ b/include/hw/virtio/vhost-backend.h
> @@ -130,6 +130,9 @@ typedef bool (*vhost_force_iommu_op)(struct vhost_dev 
> *dev);
>
>  typedef int (*vhost_set_config_call_op)(struct vhost_dev *dev,
>                                         int fd);
> +
> +typedef void (*vhost_reset_status_op)(struct vhost_dev *dev);
> +
>  typedef struct VhostOps {
>      VhostBackendType backend_type;
>      vhost_backend_init vhost_backend_init;
> @@ -177,6 +180,7 @@ typedef struct VhostOps {
>      vhost_get_device_id_op vhost_get_device_id;
>      vhost_force_iommu_op vhost_force_iommu;
>      vhost_set_config_call_op vhost_set_config_call;
> +    vhost_reset_status_op vhost_reset_status;
>  } VhostOps;
>
>  int vhost_backend_update_device_iotlb(struct vhost_dev *dev,
> diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c
> index 542e003101..28a52ddc78 100644
> --- a/hw/virtio/vhost-vdpa.c
> +++ b/hw/virtio/vhost-vdpa.c
> @@ -1132,14 +1132,23 @@ static int vhost_vdpa_dev_start(struct vhost_dev 
> *dev, bool started)
>      if (started) {
>          memory_listener_register(&v->listener, &address_space_memory);
>          return vhost_vdpa_add_status(dev, VIRTIO_CONFIG_S_DRIVER_OK);
> -    } else {
> -        vhost_vdpa_reset_device(dev);
> -        vhost_vdpa_add_status(dev, VIRTIO_CONFIG_S_ACKNOWLEDGE |
> -                                   VIRTIO_CONFIG_S_DRIVER);
> -        memory_listener_unregister(&v->listener);
> +    }
>
> -        return 0;
> +    return 0;
> +}
> +
> +static void vhost_vdpa_reset_status(struct vhost_dev *dev)
> +{
> +    struct vhost_vdpa *v = dev->opaque;
> +
> +    if (dev->vq_index + dev->nvqs != dev->vq_index_end) {
> +        return;
>      }
> +
> +    vhost_vdpa_reset_device(dev);
> +    vhost_vdpa_add_status(dev, VIRTIO_CONFIG_S_ACKNOWLEDGE |
> +                                VIRTIO_CONFIG_S_DRIVER);
> +    memory_listener_unregister(&v->listener);
>  }
>
>  static int vhost_vdpa_set_log_base(struct vhost_dev *dev, uint64_t base,
> @@ -1182,18 +1191,7 @@ 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
> @@ -1212,6 +1210,19 @@ static int vhost_vdpa_get_vring_base(struct vhost_dev 
> *dev,
>      int ret;
>
>      if (v->shadow_vqs_enabled) {
> +        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;
> +        }
> +
>          ring->num = virtio_queue_get_last_avail_idx(dev->vdev, ring->index);
>          return 0;
>      }
> @@ -1326,4 +1337,5 @@ const VhostOps vdpa_ops = {
>          .vhost_vq_get_addr = vhost_vdpa_vq_get_addr,
>          .vhost_force_iommu = vhost_vdpa_force_iommu,
>          .vhost_set_config_call = vhost_vdpa_set_config_call,
> +        .vhost_reset_status = vhost_vdpa_reset_status,

Can we simply use the NetClient stop method here?

Thanks

>  };
> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> index eb8c4c378c..a266396576 100644
> --- a/hw/virtio/vhost.c
> +++ b/hw/virtio/vhost.c
> @@ -2049,6 +2049,9 @@ void vhost_dev_stop(struct vhost_dev *hdev, 
> VirtIODevice *vdev, bool vrings)
>                               hdev->vqs + i,
>                               hdev->vq_index + i);
>      }
> +    if (hdev->vhost_ops->vhost_reset_status) {
> +        hdev->vhost_ops->vhost_reset_status(hdev);
> +    }
>
>      if (vhost_dev_has_iommu(hdev)) {
>          if (hdev->vhost_ops->vhost_set_iotlb_callback) {
> --
> 2.31.1
>