Subject: Re: [PATCH net-next] virtio_net: implement VIRTIO_CONFIG_S_NEEDS_RESET

From: "Michael S. Tsirkin" <[email-masked]>
Date: Sun, 15 Oct 2017 03:45:42 +0300

On Fri, Oct 13, 2017 at 11:51:40AM -0400, Willem de Bruijn wrote:
> From: Willem de Bruijn <[email-masked]>
> 
> Implement the reset communication request defined in the VIRTIO 1.0
> specification and introduces in Linux in commit c00bbcf862896 ("virtio:
> add VIRTIO_CONFIG_S_NEEDS_RESET device status bit").
> 
> Use the virtnet_reset function introduced in commit 2de2f7f40ef9
> ("virtio_net: XDP support for adjust_head"). That was removed in
> commit 4941d472bf95 ("virtio-net: do not reset during XDP set"),
> because no longer used. Bring it back, minus the xdp specific code.
> 
> Before tearing down any state, virtnet_freeze_down quiesces the
> device with netif_tx_disable. virtnet_reset also ensures that no
> other config operations can run concurrently.
> 
> On successful reset, the host can observe that the flag has been
> cleared. There is no need for the explicit control flag introduced
> in the previous RFC of this patch.
> 
> Changes
>   RFC -> v1
>   - drop VIRTIO_NET_CTRL_RESET_ACK message
>   - drop VIRTIO_F_CAN_RESET flag to notify guest support
> 
> Signed-off-by: Willem de Bruijn <[email-masked]>
> ---
>  drivers/net/virtio_net.c | 48 ++++++++++++++++++++++++++++++++++++++++++++----
>  1 file changed, 44 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index fc059f193e7d..8e768b54844f 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1903,13 +1903,14 @@ static const struct ethtool_ops virtnet_ethtool_ops = {
>  	.set_link_ksettings = virtnet_set_link_ksettings,
>  };
>  
> -static void virtnet_freeze_down(struct virtio_device *vdev)
> +static void virtnet_freeze_down(struct virtio_device *vdev, bool in_config)
>  {
>  	struct virtnet_info *vi = vdev->priv;
>  	int i;
>  
> -	/* Make sure no work handler is accessing the device */
> -	flush_work(&vi->config_work);
> +	/* Make sure no other work handler is accessing the device */
> +	if (!in_config)
> +		flush_work(&vi->config_work);
>  
>  	netif_device_detach(vi->dev);
>  	netif_tx_disable(vi->dev);
> @@ -1924,6 +1925,7 @@ static void virtnet_freeze_down(struct virtio_device *vdev)
>  }
>  
>  static int init_vqs(struct virtnet_info *vi);
> +static void remove_vq_common(struct virtnet_info *vi);
>  
>  static int virtnet_restore_up(struct virtio_device *vdev)
>  {
> @@ -1952,6 +1954,40 @@ static int virtnet_restore_up(struct virtio_device *vdev)
>  	return err;
>  }
>  
> +static int virtnet_reset(struct virtnet_info *vi)
> +{
> +	struct virtio_device *dev = vi->vdev;
> +	int ret;
> +
> +	virtio_config_disable(dev);
> +	dev->failed = dev->config->get_status(dev) & VIRTIO_CONFIG_S_FAILED;
> +	virtnet_freeze_down(dev, true);
> +	remove_vq_common(vi);
> +
> +	virtio_add_status(dev, VIRTIO_CONFIG_S_ACKNOWLEDGE);
> +	virtio_add_status(dev, VIRTIO_CONFIG_S_DRIVER);
> +
> +	ret = virtio_finalize_features(dev);
> +	if (ret)
> +		goto err;
> +
> +	ret = virtnet_restore_up(dev);
> +	if (ret)
> +		goto err;
> +
> +	ret = virtnet_set_queues(vi, vi->curr_queue_pairs);
> +	if (ret)
> +		goto err;
> +
> +	virtio_add_status(dev, VIRTIO_CONFIG_S_DRIVER_OK);
> +	virtio_config_enable(dev);
> +	return 0;
> +
> +err:
> +	virtio_add_status(dev, VIRTIO_CONFIG_S_FAILED);
> +	return ret;
> +}
> +
>  static int virtnet_set_guest_offloads(struct virtnet_info *vi, u64 offloads)
>  {
>  	struct scatterlist sg;

I have a question here though. How do things like MAC address
get restored?

What about the rx mode?

vlans?

Also, it seems that LINK_ANNOUNCE requests will get ignored
even if they got set before the reset, leading to downtime.

> @@ -2136,6 +2172,10 @@ static void virtnet_config_changed_work(struct work_struct *work)
>  		virtnet_ack_link_announce(vi);
>  	}
>  
> +	if (vi->vdev->config->get_status(vi->vdev) &
> +	    VIRTIO_CONFIG_S_NEEDS_RESET)
> +		virtnet_reset(vi);
> +
>  	/* Ignore unknown (future) status bits */
>  	v &= VIRTIO_NET_S_LINK_UP;
>  
> @@ -2756,7 +2796,7 @@ static __maybe_unused int virtnet_freeze(struct virtio_device *vdev)
>  	struct virtnet_info *vi = vdev->priv;
>  
>  	virtnet_cpu_notif_remove(vi);
> -	virtnet_freeze_down(vdev);
> +	virtnet_freeze_down(vdev, false);
>  	remove_vq_common(vi);
>  
>  	return 0;
> -- 
> 2.15.0.rc0.271.g36b669edcc-goog