Re: [Qemu-devel] [PATCH v1 13/16] virtio: add vhost-net migration of packed ring

[Maxime Coquelin <maxime.coquelin@redhat.com>]

On 11/22/18 3:06 PM, wexu@redhat.com wrote:
> From: Wei Xu <wexu@redhat.com>
> 
> tweaked vhost-net code to test migration.
> 
> @@ -1414,64 +1430,20 @@ long vhost_vring_ioctl(struct vhost_dev
>              r = -EFAULT;
>              break;
>          }
> +               vq->last_avail_idx = s.num & 0x7FFF;
> +               /* Forget the cached index value. */
> +               vq->avail_idx = vq->last_avail_idx;
> +               if (vhost_has_feature(vq, VIRTIO_F_RING_PACKED)) {
> +                       vq->last_avail_wrap_counter = !!(s.num & 0x8000);
> +                       vq->avail_wrap_counter = vq->last_avail_wrap_counter;
> +
> +                       vq->last_used_idx = (s.num & 0x7fFF0000) >> 16;
> +                       vq->last_used_wrap_counter = !!(s.num & 0x80000000);
> +               }
> +               break;
> +       case VHOST_GET_VRING_BASE:
> +               s.index = idx;
> +                s.num = vq->last_avail_idx;
> +               if (vhost_has_feature(vq, VIRTIO_F_RING_PACKED)) {
> +                       s.num |= vq->last_avail_wrap_counter << 15;
> +                       s.num |= vq->last_used_idx << 16;
> +                       s.num |= vq->last_used_wrap_counter << 31;

We agreed to only have avail idx and its wrap counter for vhost-user,
I guess we should have the same for Kernel backend?

This is what we have for vhost-user backend:
bit[0:14] last_avail_idx
bit[15] last_avail_wrap_counter

> +               }
> +               if (copy_to_user(argp, &s, sizeof(s)))
> +                       r = -EFAULT;
> +               break;
> 
> Signed-off-by: Wei Xu <wexu@redhat.com>
> ---
>   hw/virtio/virtio.c         | 35 ++++++++++++++++++++++++++++++-----
>   include/hw/virtio/virtio.h |  4 ++--
>   2 files changed, 32 insertions(+), 7 deletions(-)
> 
> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> index 64d5c04..7487d3d 100644
> --- a/hw/virtio/virtio.c
> +++ b/hw/virtio/virtio.c
> @@ -2963,19 +2963,40 @@ hwaddr virtio_queue_get_used_size(VirtIODevice *vdev, int n)
>       }
>   }
>   
> -uint16_t virtio_queue_get_last_avail_idx(VirtIODevice *vdev, int n)
> +int virtio_queue_get_last_avail_idx(VirtIODevice *vdev, int n)
>   {
> -    return vdev->vq[n].last_avail_idx;
> +    int idx;
> +
> +    if (virtio_host_has_feature(vdev, VIRTIO_F_RING_PACKED)) {
> +        idx = vdev->vq[n].last_avail_idx;
> +        idx |= ((int)vdev->vq[n].avail_wrap_counter) << 15;
> +        idx |= (vdev->vq[n].used_idx) << 16;
> +        idx |= ((int)vdev->vq[n].used_wrap_counter) << 31;
> +    } else {
> +        idx = (int)vdev->vq[n].last_avail_idx;
> +    }
> +    return idx;
>   }
>   
> -void virtio_queue_set_last_avail_idx(VirtIODevice *vdev, int n, uint16_t idx)
> +void virtio_queue_set_last_avail_idx(VirtIODevice *vdev, int n, int idx)
>   {
> -    vdev->vq[n].last_avail_idx = idx;
> -    vdev->vq[n].shadow_avail_idx = idx;
> +    if (virtio_vdev_has_feature(vdev, VIRTIO_F_RING_PACKED)) {
> +        vdev->vq[n].last_avail_idx = idx & 0x7fff;
> +        vdev->vq[n].avail_wrap_counter = !!(idx & 0x8000);
> +        vdev->vq[n].used_idx = (idx & 0x7fff0000) >> 16;
> +        vdev->vq[n].used_wrap_counter = !!(idx & 0x80000000);
> +    } else {
> +        vdev->vq[n].last_avail_idx = idx;
> +        vdev->vq[n].shadow_avail_idx = idx;
> +    }
>   }
>   
>   void virtio_queue_restore_last_avail_idx(VirtIODevice *vdev, int n)
>   {
> +    if (virtio_vdev_has_feature(vdev, VIRTIO_F_RING_PACKED)) {
> +        return;
> +    }
> +
>       rcu_read_lock();
>       if (vdev->vq[n].vring.desc) {
>           vdev->vq[n].last_avail_idx = vring_used_idx(&vdev->vq[n]);
> @@ -2986,6 +3007,10 @@ void virtio_queue_restore_last_avail_idx(VirtIODevice *vdev, int n)
>   
>   void virtio_queue_update_used_idx(VirtIODevice *vdev, int n)
>   {
> +    if (virtio_vdev_has_feature(vdev, VIRTIO_F_RING_PACKED)) {
> +        return;
> +    }
> +
>       rcu_read_lock();
>       if (vdev->vq[n].vring.desc) {
>           vdev->vq[n].used_idx = vring_used_idx(&vdev->vq[n]);
> diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
> index 9c1fa07..a6fdf3f 100644
> --- a/include/hw/virtio/virtio.h
> +++ b/include/hw/virtio/virtio.h
> @@ -272,8 +272,8 @@ hwaddr virtio_queue_get_used_addr(VirtIODevice *vdev, int n);
>   hwaddr virtio_queue_get_desc_size(VirtIODevice *vdev, int n);
>   hwaddr virtio_queue_get_avail_size(VirtIODevice *vdev, int n);
>   hwaddr virtio_queue_get_used_size(VirtIODevice *vdev, int n);
> -uint16_t virtio_queue_get_last_avail_idx(VirtIODevice *vdev, int n);
> -void virtio_queue_set_last_avail_idx(VirtIODevice *vdev, int n, uint16_t idx);
> +int virtio_queue_get_last_avail_idx(VirtIODevice *vdev, int n);
> +void virtio_queue_set_last_avail_idx(VirtIODevice *vdev, int n, int idx);
>   void virtio_queue_restore_last_avail_idx(VirtIODevice *vdev, int n);
>   void virtio_queue_invalidate_signalled_used(VirtIODevice *vdev, int n);
>   void virtio_queue_update_used_idx(VirtIODevice *vdev, int n);
>