Re: [PATCH net-next v2 1/2] net: netfilter: Add IPIP flowtable SW acceleration

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

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> On Fri, Jun 27, 2025 at 02:45:28PM +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):
> > 
> > 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
> >         }
> > }
> 
> Is there a proof that this accelerates forwarding?

I reproduced the scenario described above using veths (something similar to
what is done in nft_flowtable.sh) and I got the following results:

- flowtable configured as above between the two router interfaces
- TCP stream between client and server going via the IPIP tunnel
- TCP stream transmitted into the IPIP tunnel:
  - net-next:				~41Gbps
  - net-next + IPIP flowtbale support:	~40Gbps
- 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 | 28 ++++++++++++++++++++++++++--
> >  2 files changed, 47 insertions(+), 2 deletions(-)
> > 

[...]

> >  static bool nf_flow_skb_encap_protocol(struct sk_buff *skb, __be16 proto,
> >  				       u32 *offset)
> >  {
> >  	struct vlan_ethhdr *veth;
> >  	__be16 inner_proto;
> > +	u16 size;
> >  
> >  	switch (skb->protocol) {
> > +	case htons(ETH_P_IP):
> > +		if (nf_flow_ip4_encap_proto(skb, &size))
> > +			*offset += size;
> 
> This is blindly skipping the outer IP header.

Do you mean we are supposed to validate the outer IP header performing the
sanity checks done in nf_flow_tuple_ip()?

Regards,
Lorenzo

> 
> > +		return true;
> >  	case htons(ETH_P_8021Q):
> >  		if (!pskb_may_pull(skb, skb_mac_offset(skb) + sizeof(*veth)))
> >  			return false;
> > @@ -310,6 +328,7 @@ static void nf_flow_encap_pop(struct sk_buff *skb,
> >  			      struct flow_offload_tuple_rhash *tuplehash)
> >  {
> >  	struct vlan_hdr *vlan_hdr;
> > +	u16 size;
> >  	int i;
> >  
> >  	for (i = 0; i < tuplehash->tuple.encap_num; i++) {
> > @@ -331,6 +350,12 @@ static void nf_flow_encap_pop(struct sk_buff *skb,
> >  			break;
> >  		}
> >  	}
> > +
> > +	if (skb->protocol == htons(ETH_P_IP) &&
> > +	    nf_flow_ip4_encap_proto(skb, &size)) {
> > +		skb_pull(skb, size);
> > +		skb_reset_network_header(skb);
> > +	}
> 
> I have a similar patch from 2023, I think I keep somewhere in my trees.
> 
> >  }
> >  
> >  static unsigned int nf_flow_queue_xmit(struct net *net, struct sk_buff *skb,
> > @@ -357,8 +382,7 @@ nf_flow_offload_lookup(struct nf_flowtable_ctx *ctx,
> >  {
> >  	struct flow_offload_tuple tuple = {};
> >  
> > -	if (skb->protocol != htons(ETH_P_IP) &&
> > -	    !nf_flow_skb_encap_protocol(skb, htons(ETH_P_IP), &ctx->offset))
> > +	if (!nf_flow_skb_encap_protocol(skb, htons(ETH_P_IP), &ctx->offset))
> >  		return NULL;
> >  
> >  	if (nf_flow_tuple_ip(ctx, skb, &tuple) < 0)
> > 
> > -- 
> > 2.50.0
> > 
> 

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