Re: [PATCH nf-next v3 1/2] net: netfilter: Add IPIP flowtable SW acceleration

[Lorenzo Bianconi <lorenzo.bianconi@redhat.com>]

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> On Thu, Jul 03, 2025 at 04:16:02PM +0200, Lorenzo Bianconi wrote:
> > Introduce SW acceleration for IPIP tunnels in the netfilter flowtable
> > infrastructure.
> > IPIP SW acceleration can be tested running the following scenario where
> > the traffic is forwarded between two NICs (eth0 and eth1) and an IPIP
> > tunnel is used to access a remote site (using eth1 as the underlay device):
> 
> Question below.
> 
> > ETH0 -- TUN0 <==> ETH1 -- [IP network] -- TUN1 (192.168.100.2)
> > 
> > $ip addr show
> > 6: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
> >     link/ether 00:00:22:33:11:55 brd ff:ff:ff:ff:ff:ff
> >     inet 192.168.0.2/24 scope global eth0
> >        valid_lft forever preferred_lft forever
> > 7: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
> >     link/ether 00:11:22:33:11:55 brd ff:ff:ff:ff:ff:ff
> >     inet 192.168.1.1/24 scope global eth1
> >        valid_lft forever preferred_lft forever
> > 8: tun0@NONE: <POINTOPOINT,NOARP,UP,LOWER_UP> mtu 1480 qdisc noqueue state UNKNOWN group default qlen 1000
> >     link/ipip 192.168.1.1 peer 192.168.1.2
> >     inet 192.168.100.1/24 scope global tun0
> >        valid_lft forever preferred_lft forever
> > 
> > $ip route show
> > default via 192.168.100.2 dev tun0
> > 192.168.0.0/24 dev eth0 proto kernel scope link src 192.168.0.2
> > 192.168.1.0/24 dev eth1 proto kernel scope link src 192.168.1.1
> > 192.168.100.0/24 dev tun0 proto kernel scope link src 192.168.100.1
> > 
> > $nft list ruleset
> > table inet filter {
> >         flowtable ft {
> >                 hook ingress priority filter
> >                 devices = { eth0, eth1 }
> >         }
> > 
> >         chain forward {
> >                 type filter hook forward priority filter; policy accept;
> >                 meta l4proto { tcp, udp } flow add @ft
> >         }
> > }
> > 
> > Reproducing the scenario described above using veths I got the following
> > results:
> > - TCP stream transmitted into the IPIP tunnel:
> >   - net-next:				~41Gbps
> >   - net-next + IPIP flowtbale support:	~40Gbps
>                       ^^^^^^^^^
> no gain on tx side.

In this case the IPIP flowtable acceleration is effective just on the ACKs
packets so I guess it is expected we have ~ the same results. The real gain is
when the TCP stream is from the tunnel net_device to the NIC one.

> 
> > - TCP stream received from the IPIP tunnel:
> >   - net-next:				~35Gbps
> >   - net-next + IPIP flowtbale support:	~49Gbps
> > 
> > Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
> > ---
> >  net/ipv4/ipip.c                  | 21 +++++++++++++++++++++
> >  net/netfilter/nf_flow_table_ip.c | 34 ++++++++++++++++++++++++++++++++--
> >  2 files changed, 53 insertions(+), 2 deletions(-)
> > 
> > diff --git a/net/ipv4/ipip.c b/net/ipv4/ipip.c
> > index 3e03af073a1ccc3d7597a998a515b6cfdded40b5..05fb1c859170d74009d693bc8513183bdec3ff90 100644
> > --- a/net/ipv4/ipip.c
> > +++ b/net/ipv4/ipip.c
> > @@ -353,6 +353,26 @@ ipip_tunnel_ctl(struct net_device *dev, struct ip_tunnel_parm_kern *p, int cmd)
> >  	return ip_tunnel_ctl(dev, p, cmd);
> >  }
> >  
> > +static int ipip_fill_forward_path(struct net_device_path_ctx *ctx,
> > +				  struct net_device_path *path)
> > +{
> > +	struct ip_tunnel *tunnel = netdev_priv(ctx->dev);
> > +	const struct iphdr *tiph = &tunnel->parms.iph;
> > +	struct rtable *rt;
> > +
> > +	rt = ip_route_output(dev_net(ctx->dev), tiph->daddr, 0, 0, 0,
> > +			     RT_SCOPE_UNIVERSE);
> > +	if (IS_ERR(rt))
> > +		return PTR_ERR(rt);
> > +
> > +	path->type = DEV_PATH_ETHERNET;
> > +	path->dev = ctx->dev;
> > +	ctx->dev = rt->dst.dev;
> > +	ip_rt_put(rt);
> > +
> > +	return 0;
> > +}
> > +
> >  static const struct net_device_ops ipip_netdev_ops = {
> >  	.ndo_init       = ipip_tunnel_init,
> >  	.ndo_uninit     = ip_tunnel_uninit,
> > @@ -362,6 +382,7 @@ static const struct net_device_ops ipip_netdev_ops = {
> >  	.ndo_get_stats64 = dev_get_tstats64,
> >  	.ndo_get_iflink = ip_tunnel_get_iflink,
> >  	.ndo_tunnel_ctl	= ipip_tunnel_ctl,
> > +	.ndo_fill_forward_path = ipip_fill_forward_path,
> >  };
> >  
> >  #define IPIP_FEATURES (NETIF_F_SG |		\
> > diff --git a/net/netfilter/nf_flow_table_ip.c b/net/netfilter/nf_flow_table_ip.c
> > index 8cd4cf7ae21120f1057c4fce5aaca4e3152ae76d..6b55e00b1022f0a2b02d9bfd1bd34bb55c1b83f7 100644
> > --- a/net/netfilter/nf_flow_table_ip.c
> > +++ b/net/netfilter/nf_flow_table_ip.c
> > @@ -277,13 +277,37 @@ static unsigned int nf_flow_xmit_xfrm(struct sk_buff *skb,
> >  	return NF_STOLEN;
> >  }
> >  
> > +static bool nf_flow_ip4_encap_proto(struct sk_buff *skb, u16 *size)
> > +{
> > +	struct iphdr *iph;
> > +
> > +	if (!pskb_may_pull(skb, sizeof(*iph)))
> > +		return false;
> > +
> > +	iph = (struct iphdr *)skb_network_header(skb);
> > +	*size = iph->ihl << 2;
> > +
> > +	if (ip_is_fragment(iph) || unlikely(ip_has_options(*size)))
> > +		return false;
> > +
> > +	if (iph->ttl <= 1)
> > +		return false;
> > +
> > +	return iph->protocol == IPPROTO_IPIP;
> 

what kind of sanity checks are we supposed to perform? Something similar to
what we have in ip_rcv_core()?

> Once the flow is in the flowtable, it is possible to inject traffic
> with forged outer IP header, this is only looking at the inner IP
> header.

what is the difference with the plain IP/TCP use-case?

Regards,
Lorenzo

> 

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