Subject: Re: [PATCH net-next] virtio-net: ethtool configurable LRO

From: "Michael S. Tsirkin" <[email-masked]>
Date: Wed, 19 Dec 2018 18:16:03 -0500

On Wed, Dec 19, 2018 at 05:32:27PM -0500, Willem de Bruijn wrote:
> From: Willem de Bruijn <[email-masked]>
> 
> Virtio-net devices negotiate LRO support with the host.
> Display the initially negotiated state with ethtool -k.
> 
> Also allow configuring it with ethtool -K, reusing the existing
> virtnet_set_guest_offloads helper that disables LRO for XDP.
> 
> Virtio-net negotiates TSO4 and TSO6 separately, but ethtool does not
> distinguish between the two. In the unlikely legacy case where the
> host only supports one of the two, maintain the current state.
> 
> RTNL is held while calling virtnet_set_features, same as on the path
> from virtnet_xdp_set.
> 
> Tested:
>   Verified that large-receive-offload is "off [fixed]" when not
>   negotiated during initial probe and "on" otherwise.
> 
>   Measured packet size when scp-ing a large file to the guest with
>   nstat (IpExtInOctets / IpInDelivers). Verified that packet size
>   exceeds MTU only if ethtool -k shows LRO and/or GRO as enabled.
> 
> Signed-off-by: Willem de Bruijn <[email-masked]>

So I see a bug here:

	virtnet_send_command calls:
		/* Caller should know better */
		BUG_ON(!virtio_has_feature(vi->vdev, VIRTIO_NET_F_CTRL_VQ));

works fine for XDP because that checks VIRTIO_NET_F_CTRL_GUEST_OFFLOADS
in virtnet_xdp_set.

> ---
>  drivers/net/virtio_net.c | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index ea672145f6a66..9890ef30ef32e 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -2479,6 +2479,22 @@ static int virtnet_get_phys_port_name(struct net_device *dev, char *buf,
>  	return 0;
>  }
>  
> +static int virtnet_set_features(struct net_device *dev,
> +				netdev_features_t features)
> +{
> +	struct virtnet_info *vi = netdev_priv(dev);
> +	int ret = 0;
> +
> +	if ((dev->features ^ features) & NETIF_F_LRO) {
> +		if (features & NETIF_F_LRO)
> +			ret = virtnet_restore_guest_offloads(vi);
> +		else
> +			ret = virtnet_clear_guest_offloads(vi);
> +	}
> +
> +	return ret;
> +}
> +
>  static const struct net_device_ops virtnet_netdev = {
>  	.ndo_open            = virtnet_open,
>  	.ndo_stop   	     = virtnet_close,
> @@ -2493,6 +2509,7 @@ static const struct net_device_ops virtnet_netdev = {
>  	.ndo_xdp_xmit		= virtnet_xdp_xmit,
>  	.ndo_features_check	= passthru_features_check,
>  	.ndo_get_phys_port_name	= virtnet_get_phys_port_name,
> +	.ndo_set_features	= virtnet_set_features,
>  };
>  
>  static void virtnet_config_changed_work(struct work_struct *work)
> @@ -2942,6 +2959,11 @@ static int virtnet_probe(struct virtio_device *vdev)
>  			dev->hw_features |= NETIF_F_TSO6;
>  		if (virtio_has_feature(vdev, VIRTIO_NET_F_HOST_ECN))
>  			dev->hw_features |= NETIF_F_TSO_ECN;
> +		if (virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_TSO4) &&
> +		    virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_TSO6)) {
> +			dev->hw_features |= NETIF_F_LRO;
> +			dev->features |= NETIF_F_LRO;
> +		}
>  
>  		dev->features |= NETIF_F_GSO_ROBUST;
>  
> -- 
> 2.20.1.415.g653613c723-goog