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From: Ignat Korchagin <ignat@cloudflare.com>
To: "David S . Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>,
	Paolo Abeni <pabeni@redhat.com>,
	netdev@vger.kernel.org,
	linux-kernel@vger.kernel.org
Cc: kernel-team@cloudflare.com,
	Ignat Korchagin <ignat@cloudflare.com>
Subject: [PATCH] net: veth: do not manipulate GRO when using XDP
Date: Mon, 11 Mar 2024 12:40:15 +0000
Message-Id: <20240311124015.38106-1-ignat@cloudflare.com>
Precedence: bulk
MIME-Version: 1.0
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Commit d3256efd8e8b ("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 sudddenly changes, when an XDP program is attached. It also
introduces some complexities in state management as was partially addressed in
commit fe9f801355f0 ("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.

Signed-off-by: Ignat Korchagin <ignat@cloudflare.com>
---
 drivers/net/veth.c | 18 ------------------
 1 file changed, 18 deletions(-)

diff --git a/drivers/net/veth.c b/drivers/net/veth.c
index cd4a6fe458f9..f0b2c4d5fe43 100644
--- a/drivers/net/veth.c
+++ b/drivers/net/veth.c
@@ -1533,8 +1533,6 @@ 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;
 }
@@ -1638,14 +1636,6 @@ 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;
 		}
@@ -1661,14 +1651,6 @@ 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;
-- 
2.39.2