virtio-net: ethtool configurable RXCSUM

Allow user configuring RXCSUM separately with ethtool -K,
reusing the existing virtnet_set_guest_offloads helper
that configures RXCSUM for XDP. This is conditional on
VIRTIO_NET_F_CTRL_GUEST_OFFLOADS.

If Rx checksum is disabled, LRO should also be disabled.

Signed-off-by: Tonghao Zhang <xiangxia.m.yue@gmail.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Link: https://lore.kernel.org/r/20201012015820.62042-1-xiangxia.m.yue@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/virtio_net.c

@@ -68,6 +68,8 @@ static const unsigned long guest_offloads[] = {
 				(1ULL << VIRTIO_NET_F_GUEST_ECN)  | \
 				(1ULL << VIRTIO_NET_F_GUEST_UFO))
 
+#define GUEST_OFFLOAD_CSUM_MASK (1ULL << VIRTIO_NET_F_GUEST_CSUM)
+
 struct virtnet_stat_desc {
 	char desc[ETH_GSTRING_LEN];
 	size_t offset;
@@ -2522,29 +2524,48 @@ static int virtnet_get_phys_port_name(struct net_device *dev, char *buf,
 	return 0;
 }
 
+static netdev_features_t virtnet_fix_features(struct net_device *netdev,
+					      netdev_features_t features)
+{
+	/* If Rx checksum is disabled, LRO should also be disabled. */
+	if (!(features & NETIF_F_RXCSUM))
+		features &= ~NETIF_F_LRO;
+
+	return features;
+}
+
 static int virtnet_set_features(struct net_device *dev,
 				netdev_features_t features)
 {
 	struct virtnet_info *vi = netdev_priv(dev);
-	u64 offloads;
+	u64 offloads = vi->guest_offloads;
 	int err;
 
+	/* Don't allow configuration while XDP is active. */
+	if (vi->xdp_queue_pairs)
+		return -EBUSY;
+
 	if ((dev->features ^ features) & NETIF_F_LRO) {
-		if (vi->xdp_queue_pairs)
-			return -EBUSY;
-
 		if (features & NETIF_F_LRO)
-			offloads = vi->guest_offloads_capable;
+			offloads |= GUEST_OFFLOAD_LRO_MASK &
+				    vi->guest_offloads_capable;
 		else
-			offloads = vi->guest_offloads_capable &
-				   ~GUEST_OFFLOAD_LRO_MASK;
-
-		err = virtnet_set_guest_offloads(vi, offloads);
-		if (err)
-			return err;
-		vi->guest_offloads = offloads;
+			offloads &= ~GUEST_OFFLOAD_LRO_MASK;
 	}
 
+	if ((dev->features ^ features) & NETIF_F_RXCSUM) {
+		if (features & NETIF_F_RXCSUM)
+			offloads |= GUEST_OFFLOAD_CSUM_MASK &
+				    vi->guest_offloads_capable;
+		else
+			offloads &= ~GUEST_OFFLOAD_CSUM_MASK;
+	}
+
+	err = virtnet_set_guest_offloads(vi, offloads);
+	if (err)
+		return err;
+
+	vi->guest_offloads = offloads;
 	return 0;
 }
 
@@ -2563,6 +2584,7 @@ static const struct net_device_ops virtnet_netdev = {
 	.ndo_features_check	= passthru_features_check,
 	.ndo_get_phys_port_name	= virtnet_get_phys_port_name,
 	.ndo_set_features	= virtnet_set_features,
+	.ndo_fix_features	= virtnet_fix_features,
 };
 
 static void virtnet_config_changed_work(struct work_struct *work)
@@ -3013,8 +3035,10 @@ static int virtnet_probe(struct virtio_device *vdev)
 	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))
+	if (virtio_has_feature(vdev, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS)) {
+		dev->hw_features |= NETIF_F_RXCSUM;
 		dev->hw_features |= NETIF_F_LRO;
+	}
 
 	dev->vlan_features = dev->features;