Re: [PATCH v2] vdpa: Fix endian bugs in shadow virtqueue

[Eugenio Perez Martin <eperezma@redhat.com>]

On Wed, Feb 12, 2025 at 5:49 PM Konstantin Shkolnyy <kshk@linux.ibm.com> wrote:
>
> VDPA didn't work on a big-endian machine due to missing/incorrect
> CPU<->LE data format conversions.
>

Fixes: 10857ec0ad ("vhost: Add VhostShadowVirtqueue")

> Signed-off-by: Konstantin Shkolnyy <kshk@linux.ibm.com>

Acked-by: Eugenio Pérez <eperezma@redhat.com>

Thanks!

> ---
> Changes in v2: Change desc_next[] from LE format to "CPU".
>
>  hw/virtio/vhost-shadow-virtqueue.c | 18 ++++++++++--------
>  1 file changed, 10 insertions(+), 8 deletions(-)
>
> diff --git a/hw/virtio/vhost-shadow-virtqueue.c b/hw/virtio/vhost-shadow-virtqueue.c
> index 37aca8b431..4af0d7c669 100644
> --- a/hw/virtio/vhost-shadow-virtqueue.c
> +++ b/hw/virtio/vhost-shadow-virtqueue.c
> @@ -165,10 +165,10 @@ static bool vhost_svq_vring_write_descs(VhostShadowVirtqueue *svq, hwaddr *sg,
>          descs[i].len = cpu_to_le32(iovec[n].iov_len);
>
>          last = i;
> -        i = cpu_to_le16(svq->desc_next[i]);
> +        i = svq->desc_next[i];
>      }
>
> -    svq->free_head = le16_to_cpu(svq->desc_next[last]);
> +    svq->free_head = svq->desc_next[last];
>      return true;
>  }
>
> @@ -228,10 +228,12 @@ static void vhost_svq_kick(VhostShadowVirtqueue *svq)
>      smp_mb();
>
>      if (virtio_vdev_has_feature(svq->vdev, VIRTIO_RING_F_EVENT_IDX)) {
> -        uint16_t avail_event = *(uint16_t *)(&svq->vring.used->ring[svq->vring.num]);
> +        uint16_t avail_event = le16_to_cpu(
> +                *(uint16_t *)(&svq->vring.used->ring[svq->vring.num]));
>          needs_kick = vring_need_event(avail_event, svq->shadow_avail_idx, svq->shadow_avail_idx - 1);
>      } else {
> -        needs_kick = !(svq->vring.used->flags & VRING_USED_F_NO_NOTIFY);
> +        needs_kick =
> +                !(svq->vring.used->flags & cpu_to_le16(VRING_USED_F_NO_NOTIFY));
>      }
>
>      if (!needs_kick) {
> @@ -365,7 +367,7 @@ static bool vhost_svq_more_used(VhostShadowVirtqueue *svq)
>          return true;
>      }
>
> -    svq->shadow_used_idx = cpu_to_le16(*(volatile uint16_t *)used_idx);
> +    svq->shadow_used_idx = le16_to_cpu(*(volatile uint16_t *)used_idx);
>
>      return svq->last_used_idx != svq->shadow_used_idx;
>  }
> @@ -383,7 +385,7 @@ static bool vhost_svq_enable_notification(VhostShadowVirtqueue *svq)
>  {
>      if (virtio_vdev_has_feature(svq->vdev, VIRTIO_RING_F_EVENT_IDX)) {
>          uint16_t *used_event = (uint16_t *)&svq->vring.avail->ring[svq->vring.num];
> -        *used_event = svq->shadow_used_idx;
> +        *used_event = cpu_to_le16(svq->shadow_used_idx);
>      } else {
>          svq->vring.avail->flags &= ~cpu_to_le16(VRING_AVAIL_F_NO_INTERRUPT);
>      }
> @@ -408,7 +410,7 @@ static uint16_t vhost_svq_last_desc_of_chain(const VhostShadowVirtqueue *svq,
>                                               uint16_t num, uint16_t i)
>  {
>      for (uint16_t j = 0; j < (num - 1); ++j) {
> -        i = le16_to_cpu(svq->desc_next[i]);
> +        i = svq->desc_next[i];
>      }
>
>      return i;
> @@ -683,7 +685,7 @@ void vhost_svq_start(VhostShadowVirtqueue *svq, VirtIODevice *vdev,
>      svq->desc_state = g_new0(SVQDescState, svq->vring.num);
>      svq->desc_next = g_new0(uint16_t, svq->vring.num);
>      for (unsigned i = 0; i < svq->vring.num - 1; i++) {
> -        svq->desc_next[i] = cpu_to_le16(i + 1);
> +        svq->desc_next[i] = i + 1;
>      }
>  }
>
> --
> 2.34.1
>