virtio-net: ethtool configurable LRO

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 configures LRO for XDP.
This is conditional on VIRTIO_NET_F_CTRL_GUEST_OFFLOADS.

Virtio-net negotiates TSO4 and TSO6 separately, but ethtool does not
distinguish between the two. Display LRO as on only if any offload
is active.

RTNL is held while calling virtnet_set_features, same as on the path
from virtnet_xdp_set.

Changes v1 -> v2
  - allow ethtool config (-K) only if VIRTIO_NET_F_CTRL_GUEST_OFFLOADS
  - show LRO as enabled if any LRO variant is enabled
  - do not allow configuration while XDP is active
  - differentiate current features from the capable set, to restore
    on XDP down only those features that were active on XDP up
  - move test out of VIRTIO_NET_F_CSUM/TSO branch, which is tx only

Signed-off-by: Willem de Bruijn <willemb@google.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/virtio_net.c

@@ -236,6 +236,7 @@ struct virtnet_info {
 	u32 speed;
 
 	unsigned long guest_offloads;
+	unsigned long guest_offloads_capable;
 
 	/* failover when STANDBY feature enabled */
 	struct failover *failover;
@@ -2479,6 +2480,31 @@ 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);
+	u64 offloads;
+	int err;
+
+	if ((dev->features ^ features) & NETIF_F_LRO) {
+		if (vi->xdp_queue_pairs)
+			return -EBUSY;
+
+		if (features & NETIF_F_LRO)
+			offloads = vi->guest_offloads_capable;
+		else
+			offloads = 0;
+
+		err = virtnet_set_guest_offloads(vi, offloads);
+		if (err)
+			return err;
+		vi->guest_offloads = offloads;
+	}
+
+	return 0;
+}
+
 static const struct net_device_ops virtnet_netdev = {
 	.ndo_open            = virtnet_open,
 	.ndo_stop   	     = virtnet_close,
@@ -2493,6 +2519,7 @@ 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)
@@ -2951,6 +2978,11 @@ static int virtnet_probe(struct virtio_device *vdev)
 	}
 	if (virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_CSUM))
 		dev->features |= NETIF_F_RXCSUM;
+	if (virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_TSO4) ||
+	    virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_TSO6))
+		dev->features |= NETIF_F_LRO;
+	if (virtio_has_feature(vdev, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS))
+		dev->hw_features |= NETIF_F_LRO;
 
 	dev->vlan_features = dev->features;
 
@@ -3080,6 +3112,7 @@ static int virtnet_probe(struct virtio_device *vdev)
 	for (i = 0; i < ARRAY_SIZE(guest_offloads); i++)
 		if (virtio_has_feature(vi->vdev, guest_offloads[i]))
 			set_bit(guest_offloads[i], &vi->guest_offloads);
+	vi->guest_offloads_capable = vi->guest_offloads;
 
 	pr_debug("virtnet: registered device %s with %d RX and TX vq's\n",
 		 dev->name, max_queue_pairs);