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

[Willem de Bruijn <willemdebruijn.kernel@gmail.com>]

From: Willem de Bruijn <willemb@google.com>

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 <willemb@google.com>
---
 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