[PATCH 2/3] vhost: fix virtqueue access lock in datapath

[Eelco Chaudron]

On 23 Oct 2023, at 11:55, David Marchand wrote:

> Now that a r/w lock is used, the access_ok field should only be updated
> under a write lock.
>
> Since the datapath code only takes a read lock on the virtqueue to check
> access_ok, this lock must be released and a write lock taken before
> calling vring_translate().
>
> Fixes: 03f77d66d966 ("vhost: change virtqueue access lock to a read/write one")
> Cc: stable at dpdk.org
>
> Signed-off-by: David Marchand <david.marchand at redhat.com>

Only one question, but whatever the outcome is the change looks good to me.

Acked-by: Eelco Chaudron <echaudro at redhat.com>

> ---
>  lib/vhost/virtio_net.c | 60 +++++++++++++++++++++++++++++++-----------
>  1 file changed, 44 insertions(+), 16 deletions(-)
>
> diff --git a/lib/vhost/virtio_net.c b/lib/vhost/virtio_net.c
> index 759a78e3e3..4116f79d4f 100644
> --- a/lib/vhost/virtio_net.c
> +++ b/lib/vhost/virtio_net.c
> @@ -1694,6 +1694,17 @@ virtio_dev_rx_packed(struct virtio_net *dev,
>  	return pkt_idx;
>  }
>
> +static void
> +virtio_dev_vring_translate(struct virtio_net *dev, struct vhost_virtqueue *vq)
> +{

Would it be an idea to annotate this function that it needs to be called with the “read locks” (and that it will free them) to avoid the duplicate:

+		vhost_user_iotlb_rd_unlock(vq);
+		rte_rwlock_read_unlock(&vq->access_lock);

> +	rte_rwlock_write_lock(&vq->access_lock);
> +	vhost_user_iotlb_rd_lock(vq);
> +	if (!vq->access_ok)
> +		vring_translate(dev, vq);
> +	vhost_user_iotlb_rd_unlock(vq);
> +	rte_rwlock_write_unlock(&vq->access_lock);
> +}
> +
>  static __rte_always_inline uint32_t
>  virtio_dev_rx(struct virtio_net *dev, struct vhost_virtqueue *vq,
>  	struct rte_mbuf **pkts, uint32_t count)
> @@ -1708,9 +1719,13 @@ virtio_dev_rx(struct virtio_net *dev, struct vhost_virtqueue *vq,
>
>  	vhost_user_iotlb_rd_lock(vq);
>
> -	if (unlikely(!vq->access_ok))
> -		if (unlikely(vring_translate(dev, vq) < 0))
> -			goto out;
> +	if (unlikely(!vq->access_ok)) {
> +		vhost_user_iotlb_rd_unlock(vq);
> +		rte_rwlock_read_unlock(&vq->access_lock);
> +
> +		virtio_dev_vring_translate(dev, vq);
> +		goto out_no_unlock;
> +	}
>
>  	count = RTE_MIN((uint32_t)MAX_PKT_BURST, count);
>  	if (count == 0)
> @@ -1729,6 +1744,7 @@ virtio_dev_rx(struct virtio_net *dev, struct vhost_virtqueue *vq,
>  out_access_unlock:
>  	rte_rwlock_read_unlock(&vq->access_lock);
>
> +out_no_unlock:
>  	return nb_tx;
>  }
>
> @@ -2523,9 +2539,13 @@ virtio_dev_rx_async_submit(struct virtio_net *dev, struct vhost_virtqueue *vq,
>
>  	vhost_user_iotlb_rd_lock(vq);
>
> -	if (unlikely(!vq->access_ok))
> -		if (unlikely(vring_translate(dev, vq) < 0))
> -			goto out;
> +	if (unlikely(!vq->access_ok)) {
> +		vhost_user_iotlb_rd_unlock(vq);
> +		rte_rwlock_read_unlock(&vq->access_lock);
> +
> +		virtio_dev_vring_translate(dev, vq);
> +		goto out_no_unlock;
> +	}
>
>  	count = RTE_MIN((uint32_t)MAX_PKT_BURST, count);
>  	if (count == 0)
> @@ -2546,6 +2566,7 @@ virtio_dev_rx_async_submit(struct virtio_net *dev, struct vhost_virtqueue *vq,
>  out_access_unlock:
>  	rte_rwlock_write_unlock(&vq->access_lock);
>
> +out_no_unlock:
>  	return nb_tx;
>  }
>
> @@ -3576,11 +3597,13 @@ rte_vhost_dequeue_burst(int vid, uint16_t queue_id,
>
>  	vhost_user_iotlb_rd_lock(vq);
>
> -	if (unlikely(!vq->access_ok))
> -		if (unlikely(vring_translate(dev, vq) < 0)) {
> -			count = 0;
> -			goto out;
> -		}
> +	if (unlikely(!vq->access_ok)) {
> +		vhost_user_iotlb_rd_unlock(vq);
> +		rte_rwlock_read_unlock(&vq->access_lock);
> +
> +		virtio_dev_vring_translate(dev, vq);
> +		goto out_no_unlock;
> +	}
>
>  	/*
>  	 * Construct a RARP broadcast packet, and inject it to the "pkts"
> @@ -3641,6 +3664,7 @@ rte_vhost_dequeue_burst(int vid, uint16_t queue_id,
>  	if (unlikely(rarp_mbuf != NULL))
>  		count += 1;
>
> +out_no_unlock:
>  	return count;
>  }
>
> @@ -4190,11 +4214,14 @@ rte_vhost_async_try_dequeue_burst(int vid, uint16_t queue_id,
>
>  	vhost_user_iotlb_rd_lock(vq);
>
> -	if (unlikely(vq->access_ok == 0))
> -		if (unlikely(vring_translate(dev, vq) < 0)) {
> -			count = 0;
> -			goto out;
> -		}
> +	if (unlikely(vq->access_ok == 0)) {
> +		vhost_user_iotlb_rd_unlock(vq);
> +		rte_rwlock_read_unlock(&vq->access_lock);
> +
> +		virtio_dev_vring_translate(dev, vq);
> +		count = 0;
> +		goto out_no_unlock;
> +	}
>
>  	/*
>  	 * Construct a RARP broadcast packet, and inject it to the "pkts"
> @@ -4260,5 +4287,6 @@ rte_vhost_async_try_dequeue_burst(int vid, uint16_t queue_id,
>  	if (unlikely(rarp_mbuf != NULL))
>  		count += 1;
>
> +out_no_unlock:
>  	return count;
>  }
> -- 
> 2.41.0