Subject: Re: [PATCH RFC 1/2] virtio_net: implement VIRTIO_CONFIG_S_NEEDS_RESET

From: "Michael S. Tsirkin" <[email-masked]>
Date: Tue, 29 Aug 2017 23:20:33 +0300

On Tue, Aug 29, 2017 at 04:07:58PM -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").
> 
> Since that patch, the virtio-net driver has added a virtnet_reset
> function that implements the requested behavior through calls to the
> power management freeze and restore functions.
> 
> That function has recently been reverted when its sole caller was
> updated. Bring it back and listen for the request from the host on
> the config channel.
> 
> Implement the feature analogous to other config requests. In
> particular, acknowledge the request in the same manner as the
> NET_S_ANNOUNCE link announce request, by responding with a new
> VIRTIO_NET_CTRL_${TYPE} command. On reception, the host must check
> the config status register for success or failure.

Pls make it clearer why do you need these interface extensions.

> The existing freeze handler verifies that no config changes are
> running concurrently. Elide this check for reset. The request is
> always handled from the config workqueue. No other config requests
> can be active or scheduled concurrently on vi->config.

You need to prevent packet TX from being in progress.

> 
> Signed-off-by: Willem de Bruijn <[email-masked]>
> ---
>  drivers/net/virtio_net.c        | 69 +++++++++++++++++++++++++++++++++++------
>  include/uapi/linux/virtio_net.h |  4 +++

virtio dev or another virtio TC list must be Cc'd on any proposed API changes.

>  2 files changed, 64 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 52ae78ca3d38..5e349226f7c1 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1458,12 +1458,11 @@ static void virtnet_netpoll(struct net_device *dev)
>  }
>  #endif
>  
> -static void virtnet_ack_link_announce(struct virtnet_info *vi)
> +static void virtnet_ack(struct virtnet_info *vi, u8 class, u8 cmd)
>  {
>  	rtnl_lock();
> -	if (!virtnet_send_command(vi, VIRTIO_NET_CTRL_ANNOUNCE,
> -				  VIRTIO_NET_CTRL_ANNOUNCE_ACK, NULL))
> -		dev_warn(&vi->dev->dev, "Failed to ack link announce.\n");
> +	if (!virtnet_send_command(vi, class, cmd, NULL))
> +		dev_warn(&vi->dev->dev, "Failed to ack %u.%u\n", class, cmd);
>  	rtnl_unlock();
>  }
>  
> @@ -1857,13 +1856,16 @@ 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_reset)
>  {
>  	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 work handler is accessing the device,
> +	 * unless this call is made from the reset work handler itself.
> +	 */
> +	if (!in_reset)
> +		flush_work(&vi->config_work);
>  
>  	netif_device_detach(vi->dev);
>  	netif_tx_disable(vi->dev);
> @@ -1878,6 +1880,7 @@ 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)
>  {
> @@ -1906,6 +1909,45 @@ 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;
> +	bool failed;
> +	int ret;
> +
> +	virtio_config_disable(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);
> +
> +	/* Restore the failed status (see virtio_device_restore). */
> +	if (failed)
> +		virtio_add_status(dev, VIRTIO_CONFIG_S_FAILED);
> +
> +	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;
> @@ -2085,7 +2127,16 @@ static void virtnet_config_changed_work(struct work_struct *work)
>  
>  	if (v & VIRTIO_NET_S_ANNOUNCE) {
>  		netdev_notify_peers(vi->dev);
> -		virtnet_ack_link_announce(vi);
> +		virtnet_ack(vi, VIRTIO_NET_CTRL_ANNOUNCE,
> +			    VIRTIO_NET_CTRL_ANNOUNCE_ACK);
> +	}
> +
> +	if (vi->vdev->config->get_status(vi->vdev) &
> +	    VIRTIO_CONFIG_S_NEEDS_RESET) {
> +		virtnet_reset(vi);
> +		virtnet_ack(vi, VIRTIO_NET_CTRL_RESET,
> +			    VIRTIO_NET_CTRL_RESET_ACK);
> +
>  	}
>  
>  	/* Ignore unknown (future) status bits */
> @@ -2708,7 +2759,7 @@ 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;
> diff --git a/include/uapi/linux/virtio_net.h b/include/uapi/linux/virtio_net.h
> index fc353b518288..188fdc528f13 100644
> --- a/include/uapi/linux/virtio_net.h
> +++ b/include/uapi/linux/virtio_net.h
> @@ -245,4 +245,8 @@ struct virtio_net_ctrl_mq {
>  #define VIRTIO_NET_CTRL_GUEST_OFFLOADS   5
>  #define VIRTIO_NET_CTRL_GUEST_OFFLOADS_SET        0
>  
> +/* Signal that the driver received and executed the reset command. */
> +#define VIRTIO_NET_CTRL_RESET			6
> +#define VIRTIO_NET_CTRL_RESET_ACK		0
> +
>  #endif /* _UAPI_LINUX_VIRTIO_NET_H */
> -- 
> 2.14.1.342.g6490525c54-goog