netdev - Re: [PATCH bpf] selftests/bpf: fix xdp_redirect xdp-features for xdp

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Date:   Sat, 15 Apr 2023 13:06:18 +0200
From:   Lorenzo Bianconi <lorenzo@...nel.org>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org,
        lorenzo.bianconi@...hat.com, ast@...nel.org, andrii@...nel.org,
        martin.lau@...ux.dev, joamaki@...il.com
Subject: Re: [PATCH bpf] selftests/bpf: fix xdp_redirect xdp-features for
 xdp_bonding selftest

> On 4/15/23 12:10 AM, Lorenzo Bianconi wrote:
> > > On 4/14/23 11:21 PM, Lorenzo Bianconi wrote:
> > > > NETDEV_XDP_ACT_NDO_XMIT is not enabled by default for veth driver but it
> > > > depends on the device configuration. Fix XDP_REDIRECT xdp-features in
> > > > xdp_bonding selftest loading a dummy XDP program on veth2_2 device.
> > > > 
> > > > Fixes: fccca038f300 ("veth: take into account device reconfiguration for xdp_features flag")
> > > 
> > > Hm, does that mean we're changing^breaking existing user behavior iff after
> > > fccca038f300 you can only make it work by loading dummy prog?
> > 
> > nope, even before in order to enable ndo_xdp_xmit for veth you should load a dummy
> > program on the device peer or enable gro on the device peer:
> > 
> > https://github.com/torvalds/linux/blob/master/drivers/net/veth.c#L477
> > 
> > we are just reflecting this behaviour in the xdp_features flag.
> 
> Ok, I'm confused then why it passed before?

ack, you are right. I guess the issue is in veth driver code. In order to
enable NETDEV_XDP_ACT_NDO_XMIT for device "veth0", we need to check the peer
veth1 configuration since the check in veth_xdp_xmit() is on the peer rx queue.
Something like:

diff --git a/drivers/net/veth.c b/drivers/net/veth.c
index e1b38fbf1dd9..4b3c6647edc6 100644
--- a/drivers/net/veth.c
+++ b/drivers/net/veth.c
@@ -1262,11 +1262,12 @@ static void veth_set_xdp_features(struct net_device *dev)
 
 	peer = rtnl_dereference(priv->peer);
 	if (peer && peer->real_num_tx_queues <= dev->real_num_rx_queues) {
+		struct veth_priv *priv_peer = netdev_priv(peer);
 		xdp_features_t val = NETDEV_XDP_ACT_BASIC |
 				     NETDEV_XDP_ACT_REDIRECT |
 				     NETDEV_XDP_ACT_RX_SG;
 
-		if (priv->_xdp_prog || veth_gro_requested(dev))
+		if (priv_peer->_xdp_prog || veth_gro_requested(peer))
 			val |= NETDEV_XDP_ACT_NDO_XMIT |
 			       NETDEV_XDP_ACT_NDO_XMIT_SG;
 		xdp_set_features_flag(dev, val);
@@ -1504,19 +1505,23 @@ static int veth_set_features(struct net_device *dev,
 {
 	netdev_features_t changed = features ^ dev->features;
 	struct veth_priv *priv = netdev_priv(dev);
+	struct net_device *peer;
 	int err;
 
 	if (!(changed & NETIF_F_GRO) || !(dev->flags & IFF_UP) || priv->_xdp_prog)
 		return 0;
 
+	peer = rtnl_dereference(priv->peer);
 	if (features & NETIF_F_GRO) {
 		err = veth_napi_enable(dev);
 		if (err)
 			return err;
 
-		xdp_features_set_redirect_target(dev, true);
+		if (peer)
+			xdp_features_set_redirect_target(peer, true);
 	} else {
-		xdp_features_clear_redirect_target(dev);
+		if (peer)
+			xdp_features_clear_redirect_target(peer);
 		veth_napi_del(dev);
 	}
 	return 0;
@@ -1598,13 +1603,13 @@ static int veth_xdp_set(struct net_device *dev, struct bpf_prog *prog,
 			peer->max_mtu = max_mtu;
 		}
 
-		xdp_features_set_redirect_target(dev, true);
+		xdp_features_set_redirect_target(peer, true);
 	}
 
 	if (old_prog) {
 		if (!prog) {
-			if (!veth_gro_requested(dev))
-				xdp_features_clear_redirect_target(dev);
+			if (peer && !veth_gro_requested(dev))
+				xdp_features_clear_redirect_target(peer);
 
 			if (dev->flags & IFF_UP)
 				veth_disable_xdp(dev);

What do you think?

Regards,
Lorenzo

> 
> > > > Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>
> > > > ---
> > > >    tools/testing/selftests/bpf/prog_tests/xdp_bonding.c | 11 +++++++++++
> > > >    1 file changed, 11 insertions(+)
> > > > 
> > > > diff --git a/tools/testing/selftests/bpf/prog_tests/xdp_bonding.c b/tools/testing/selftests/bpf/prog_tests/xdp_bonding.c
> > > > index 5e3a26b15ec6..dcbe30c81291 100644
> > > > --- a/tools/testing/selftests/bpf/prog_tests/xdp_bonding.c
> > > > +++ b/tools/testing/selftests/bpf/prog_tests/xdp_bonding.c
> > > > @@ -168,6 +168,17 @@ static int bonding_setup(struct skeletons *skeletons, int mode, int xmit_policy,
> > > >    		if (xdp_attach(skeletons, skeletons->xdp_dummy->progs.xdp_dummy_prog, "veth1_2"))
> > > >    			return -1;
> > > > +
> > > > +		if (!ASSERT_OK(setns_by_name("ns_dst"), "set netns to ns_dst"))
> > > > +			return -1;
> > > > +
> > > > +		/* Load a dummy XDP program on veth2_2 in order to enable
> > > > +		 * NETDEV_XDP_ACT_NDO_XMIT feature
> > > > +		 */
> > > > +		if (xdp_attach(skeletons, skeletons->xdp_dummy->progs.xdp_dummy_prog, "veth2_2"))
> > > > +			return -1;
> > > > +
> > > > +		restore_root_netns();
> > > >    	}
> > > >    	SYS("ip -netns ns_dst link set veth2_1 master bond2");

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