Re: [PATCH 4/4] virtio-net: sleep instead of busy waiting for cvq command

[Xuan Zhuo]

On Mon, 26 Dec 2022 15:49:08 +0800, Jason Wang <jasowang@xxxxxxxxxx> wrote:
> We used to busy waiting on the cvq command this tends to be
> problematic since:
>
> 1) CPU could wait for ever on a buggy/malicous device
> 2) There's no wait to terminate the process that triggers the cvq
>    command
>
> So this patch switch to use virtqueue_wait_for_used() to sleep with a
> timeout (1s) instead of busy polling for the cvq command forever. This

I don't think that a fixed 1S is a good choice. Some of the DPUs are very
lazy for cvq handle. In particular, we will also directly break the device.

I think it is necessary to add a Virtio-Net parameter to allow users to define
this timeout by themselves. Although I don't think this is a good way.

Thanks.


> gives the scheduler a breath and can let the process can respond to
> asignal. If the device doesn't respond in the timeout, break the
> device.
>
> Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
> ---
> Changes since V1:
> - break the device when timeout
> - get buffer manually since the virtio core check more_used() instead
> ---
>  drivers/net/virtio_net.c | 24 ++++++++++++++++--------
>  1 file changed, 16 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index efd9dd55828b..6a2ea64cfcb5 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -405,6 +405,7 @@ static void disable_rx_mode_work(struct virtnet_info *vi)
>  	vi->rx_mode_work_enabled = false;
>  	spin_unlock_bh(&vi->rx_mode_lock);
>
> +	virtqueue_wake_up(vi->cvq);
>  	flush_work(&vi->rx_mode_work);
>  }
>
> @@ -1497,6 +1498,11 @@ static bool try_fill_recv(struct virtnet_info *vi, struct receive_queue *rq,
>  	return !oom;
>  }
>
> +static void virtnet_cvq_done(struct virtqueue *cvq)
> +{
> +	virtqueue_wake_up(cvq);
> +}
> +
>  static void skb_recv_done(struct virtqueue *rvq)
>  {
>  	struct virtnet_info *vi = rvq->vdev->priv;
> @@ -1984,6 +1990,8 @@ static int virtnet_tx_resize(struct virtnet_info *vi,
>  	return err;
>  }
>
> +static int virtnet_close(struct net_device *dev);
> +
>  /*
>   * Send command via the control virtqueue and check status.  Commands
>   * supported by the hypervisor, as indicated by feature bits, should
> @@ -2026,14 +2034,14 @@ static bool virtnet_send_command(struct virtnet_info *vi, u8 class, u8 cmd,
>  	if (unlikely(!virtqueue_kick(vi->cvq)))
>  		return vi->ctrl->status == VIRTIO_NET_OK;
>
> -	/* Spin for a response, the kick causes an ioport write, trapping
> -	 * into the hypervisor, so the request should be handled immediately.
> -	 */
> -	while (!virtqueue_get_buf(vi->cvq, &tmp) &&
> -	       !virtqueue_is_broken(vi->cvq))
> -		cpu_relax();
> +	if (virtqueue_wait_for_used(vi->cvq)) {
> +		virtqueue_get_buf(vi->cvq, &tmp);
> +		return vi->ctrl->status == VIRTIO_NET_OK;
> +	}
>
> -	return vi->ctrl->status == VIRTIO_NET_OK;
> +	netdev_err(vi->dev, "CVQ command timeout, break the virtio device.");
> +	virtio_break_device(vi->vdev);
> +	return VIRTIO_NET_ERR;
>  }
>
>  static int virtnet_set_mac_address(struct net_device *dev, void *p)
> @@ -3526,7 +3534,7 @@ static int virtnet_find_vqs(struct virtnet_info *vi)
>
>  	/* Parameters for control virtqueue, if any */
>  	if (vi->has_cvq) {
> -		callbacks[total_vqs - 1] = NULL;
> +		callbacks[total_vqs - 1] = virtnet_cvq_done;
>  		names[total_vqs - 1] = "control";
>  	}
>
> --
> 2.25.1
>
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