Re: [PATCH nf-next v9 2/3] net: netfilter: Add IPIP flowtable tx sw acceleration

[Pablo Neira Ayuso <pablo@netfilter.org>]

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Hi Lorenzo,

On Fri, Nov 07, 2025 at 12:14:47PM +0100, Lorenzo Bianconi wrote:
[...]
> @@ -565,8 +622,9 @@ nf_flow_offload_ip_hook(void *priv, struct sk_buff *skb,
>  
>  	dir = tuplehash->tuple.dir;
>  	flow = container_of(tuplehash, struct flow_offload, tuplehash[dir]);
> +	other_tuple = &flow->tuplehash[!dir].tuple;
>  
> -	if (nf_flow_encap_push(skb, &flow->tuplehash[!dir].tuple) < 0)
> +	if (nf_flow_encap_push(state->net, skb, other_tuple))
>  		return NF_DROP;
>  
>  	switch (tuplehash->tuple.xmit_type) {
> @@ -577,7 +635,9 @@ nf_flow_offload_ip_hook(void *priv, struct sk_buff *skb,
>  			flow_offload_teardown(flow);
>  			return NF_DROP;
>  		}
> -		neigh = ip_neigh_gw4(rt->dst.dev, rt_nexthop(rt, flow->tuplehash[!dir].tuple.src_v4.s_addr));
> +		dest = other_tuple->tun_num ? other_tuple->tun.src_v4.s_addr
> +					    : other_tuple->src_v4.s_addr;

I think this can be simplified if my series use the ip_hdr(skb)->daddr
for rt_nexthop(), see attached patch. This would be fetched _before_
pushing the tunnel and layer 2 encapsulation headers. Then, there is
no need to fetch other_tuple and check if tun_num is greater than
zero.

See my sketch patch, I am going to give this a try, if this is
correct, I would need one more iteration from you.

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diff --git a/net/netfilter/nf_flow_table_ip.c b/net/netfilter/nf_flow_table_ip.c
index 8b74fb34998e..ff2b6c16c715 100644
--- a/net/netfilter/nf_flow_table_ip.c
+++ b/net/netfilter/nf_flow_table_ip.c
@@ -427,6 +427,7 @@ nf_flow_offload_ip_hook(void *priv, struct sk_buff *skb,
 	struct flow_offload *flow;
 	struct neighbour *neigh;
 	struct rtable *rt;
+	__be32 ip_dst;
 	int ret;
 
 	tuplehash = nf_flow_offload_lookup(&ctx, flow_table, skb);
@@ -449,6 +450,7 @@ nf_flow_offload_ip_hook(void *priv, struct sk_buff *skb,
 
 	dir = tuplehash->tuple.dir;
 	flow = container_of(tuplehash, struct flow_offload, tuplehash[dir]);
+	ip_dst = ip_hdr(skb)->daddr;
 
 	switch (tuplehash->tuple.xmit_type) {
 	case FLOW_OFFLOAD_XMIT_NEIGH:
@@ -458,7 +460,7 @@ nf_flow_offload_ip_hook(void *priv, struct sk_buff *skb,
 			flow_offload_teardown(flow);
 			return NF_DROP;
 		}
-		neigh = ip_neigh_gw4(rt->dst.dev, rt_nexthop(rt, flow->tuplehash[!dir].tuple.src_v4.s_addr));
+		neigh = ip_neigh_gw4(rt->dst.dev, rt_nexthop(rt, ip_dst));
 		if (IS_ERR(neigh)) {
 			flow_offload_teardown(flow);
 			return NF_DROP;