Re: [RFC PATCH] virtio-net: use NETIF_F_GRO_HW instead of NETIF_F_LRO

Commit a02e8964eaf92 ("virtio-net: ethtool configurable LRO") tries to
advertise LRO on behalf of the guest offloading features and allow the
administrator to enable and disable those features via ethtool.

This may lead several issues:

- For the device that doesn't support control guest offloads, the
  "LRO" can't be disabled so we will get a warn in the
  dev_disable_lro()
- For the device that have the control guest offloads, the guest
  offloads were disabled in the case of bridge etc which may slow down
  the traffic.

Try to fix this by using NETIF_F_GRO_HW instead so we're not
guaranteed to be re-segmented as original. Or we may want a new netdev
feature like RX_GSO since the guest offloads for virtio-net is
actually to receive GSO packet.

Or we can try not advertise LRO is control guest offloads is not
enabled. This solves the warning but will still slow down the traffic.

Signed-off-by: Jason Wang <redacted>
---
 drivers/net/virtio_net.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 0416a7e00914..10c382b08bce 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c

@@ -63,7 +63,7 @@ static const unsigned long guest_offloads[] = {
        VIRTIO_NET_F_GUEST_CSUM
 };

-#define GUEST_OFFLOAD_LRO_MASK ((1ULL << VIRTIO_NET_F_GUEST_TSO4) | \
+#define GUEST_OFFLOAD_GRO_HW_MASK ((1ULL << VIRTIO_NET_F_GUEST_TSO4) | \
                                (1ULL << VIRTIO_NET_F_GUEST_TSO6) | \
                                (1ULL << VIRTIO_NET_F_GUEST_ECN)  | \
                                (1ULL << VIRTIO_NET_F_GUEST_UFO))

@@ -2481,7 +2481,7 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog,
                virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_ECN) ||
                virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_UFO) ||
                virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_CSUM))) {
-               NL_SET_ERR_MSG_MOD(extack, "Can't set XDP while host is implementing LRO/CSUM, disable LRO/CSUM first");
+               NL_SET_ERR_MSG_MOD(extack, "Can't set XDP while host is implementing GRO_HW/CSUM, disable GRO_HW/CSUM first");
                return -EOPNOTSUPP;
        }

@@ -2612,15 +2612,15 @@ static int virtnet_set_features(struct net_device *dev,
        u64 offloads;
        int err;

-       if ((dev->features ^ features) & NETIF_F_LRO) {
+       if ((dev->features ^ features) & NETIF_F_GRO_HW) {
                if (vi->xdp_enabled)
                        return -EBUSY;

-               if (features & NETIF_F_LRO)
+               if (features & NETIF_F_GRO_HW)
                        offloads = vi->guest_offloads_capable;
                else
                        offloads = vi->guest_offloads_capable &
-                                  ~GUEST_OFFLOAD_LRO_MASK;
+                                  ~GUEST_OFFLOAD_GRO_HW_MASK;

                err = virtnet_set_guest_offloads(vi, offloads);
                if (err)

@@ -3100,9 +3100,9 @@ static int virtnet_probe(struct virtio_device *vdev)
                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;
+               dev->features |= NETIF_F_GRO_HW;
        if (virtio_has_feature(vdev, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS))
-               dev->hw_features |= NETIF_F_LRO;
+               dev->hw_features |= NETIF_F_GRO_HW;

        dev->vlan_features = dev->features;

--