net: veth: do not manipulate GRO when using XDP

Commit d3256efd ("veth: allow enabling NAPI even without XDP") tried to fix
the fact that GRO was not possible without XDP, because veth did not use NAPI
without XDP. However, it also introduced the behaviour that GRO is always
enabled, when XDP is enabled.

While it might be desired for most cases, it is confusing for the user at best
as the GRO flag suddenly changes, when an XDP program is attached. It also
introduces some complexities in state management as was partially addressed in
commit fe9f8013 ("net: veth: clear GRO when clearing XDP even when down").

But the biggest problem is that it is not possible to disable GRO at all, when
an XDP program is attached, which might be needed for some use cases.

Fix this by not touching the GRO flag on XDP enable/disable as the code already
supports switching to NAPI if either GRO or XDP is requested.

Link: https://lore.kernel.org/lkml/20240311124015.38106-1-ignat@cloudflare.com/
Fixes: d3256efd ("veth: allow enabling NAPI even without XDP")
Fixes: fe9f8013 ("net: veth: clear GRO when clearing XDP even when down")
Signed-off-by: Ignat Korchagin <ignat@cloudflare.com>
Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/veth.c

@@ -1464,8 +1464,6 @@ static netdev_features_t veth_fix_features(struct net_device *dev,
 		if (peer_priv->_xdp_prog)
 			features &= ~NETIF_F_GSO_SOFTWARE;
 	}
-	if (priv->_xdp_prog)
-		features |= NETIF_F_GRO;
 
 	return features;
 }
@@ -1569,14 +1567,6 @@ static int veth_xdp_set(struct net_device *dev, struct bpf_prog *prog,
 		}
 
 		if (!old_prog) {
-			if (!veth_gro_requested(dev)) {
-				/* user-space did not require GRO, but adding
-				 * XDP is supposed to get GRO working
-				 */
-				dev->features |= NETIF_F_GRO;
-				netdev_features_change(dev);
-			}
-
 			peer->hw_features &= ~NETIF_F_GSO_SOFTWARE;
 			peer->max_mtu = max_mtu;
 		}
@@ -1592,14 +1582,6 @@ static int veth_xdp_set(struct net_device *dev, struct bpf_prog *prog,
 			if (dev->flags & IFF_UP)
 				veth_disable_xdp(dev);
 
-			/* if user-space did not require GRO, since adding XDP
-			 * enabled it, clear it now
-			 */
-			if (!veth_gro_requested(dev)) {
-				dev->features &= ~NETIF_F_GRO;
-				netdev_features_change(dev);
-			}
-
 			if (peer) {
 				peer->hw_features |= NETIF_F_GSO_SOFTWARE;
 				peer->max_mtu = ETH_MAX_MTU;