RE: [PATCH v2 2/2] vhost: fix slot index calculation in async vhost

["Xia, Chenbo" <chenbo.xia@intel.com>]

> -----Original Message-----
> From: Jiang, Cheng1 <cheng1.jiang@intel.com>
> Sent: Tuesday, October 11, 2022 11:08 AM
> To: maxime.coquelin@redhat.com; Xia, Chenbo <chenbo.xia@intel.com>
> Cc: dev@dpdk.org; Hu, Jiayu <jiayu.hu@intel.com>; Ding, Xuan
> <xuan.ding@intel.com>; Ma, WenwuX <wenwux.ma@intel.com>; Wang, YuanX
> <yuanx.wang@intel.com>; Yang, YvonneX <yvonnex.yang@intel.com>; He,
> Xingguang <xingguang.he@intel.com>; Jiang, Cheng1 <cheng1.jiang@intel.com>;
> stable@dpdk.org
> Subject: [PATCH v2 2/2] vhost: fix slot index calculation in async vhost
> 
> When the packet receiving failure and the DMA ring full occur
> simultaneously in the asynchronous vhost, the slot_idx needs to be
> decreased by 1. For packed virtqueue, the slot index should be
> ring_size - 1, if the slot_idx is currently 0, since the ring size is
> not necessarily the power of 2.
> 
> Fixes: 84d5204310d7 ("vhost: support async dequeue for split ring")
> Fixes: fe8477ebbd94 ("vhost: support async packed ring dequeue")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Cheng Jiang <cheng1.jiang@intel.com>
> ---
>  lib/vhost/virtio_net.c | 16 ++++++++++++++--
>  1 file changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/vhost/virtio_net.c b/lib/vhost/virtio_net.c
> index 457ac2e92a..efebd063d7 100644
> --- a/lib/vhost/virtio_net.c
> +++ b/lib/vhost/virtio_net.c
> @@ -3457,6 +3457,7 @@ virtio_dev_tx_async_split(struct virtio_net *dev,
> struct vhost_virtqueue *vq,
>  				allocerr_warned = true;
>  			}
>  			dropped = true;
> +			slot_idx--;
>  			break;
>  		}
> 
> @@ -3647,6 +3648,12 @@ virtio_dev_tx_async_packed(struct virtio_net *dev,
> struct vhost_virtqueue *vq,
>  		if (unlikely(virtio_dev_tx_async_single_packed(dev, vq,
> mbuf_pool, pkt,
>  				slot_idx, legacy_ol_flags))) {
>  			rte_pktmbuf_free_bulk(&pkts_prealloc[pkt_idx], count -
> pkt_idx);
> +
> +			if (slot_idx == 0)
> +				slot_idx = vq->size - 1;
> +			else
> +				slot_idx--;
> +
>  			break;
>  		}
> 
> @@ -3674,8 +3681,13 @@ virtio_dev_tx_async_packed(struct virtio_net *dev,
> struct vhost_virtqueue *vq,
>  			async->buffer_idx_packed += vq->size - pkt_err;
> 
>  		while (pkt_err-- > 0) {
> -			rte_pktmbuf_free(pkts_info[slot_idx % vq->size].mbuf);
> -			slot_idx--;
> +			rte_pktmbuf_free(pkts_info[slot_idx].mbuf);
> +			descs_err += pkts_info[slot_idx].descs;
> +
> +			if (slot_idx == 0)
> +				slot_idx = vq->size - 1;
> +			else
> +				slot_idx--;
>  		}
> 
>  		/* recover available ring */
> --
> 2.35.1

Reviewed-by: Chenbo Xia <chenbo.xia@intel.com>