netdev - Re: [PATCH netfilter] Fix hw flow offload from nftables

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Date: Mon, 23 Oct 2023 12:24:17 +0200
From: Pablo Neira Ayuso <pablo@...filter.org>
To: Donald Hunter <donald.hunter@...il.com>
Cc: Jozsef Kadlecsik <kadlec@...filter.org>,
	Florian Westphal <fw@...len.de>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Paul Blakey <paulb@...dia.com>, Vlad Buslov <vladbu@...dia.com>,
	netfilter-devel@...r.kernel.org, coreteam@...filter.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH netfilter] Fix hw flow offload from nftables

On Mon, Oct 23, 2023 at 11:13:47AM +0100, Donald Hunter wrote:
> The NF_FLOW_HW_ESTABLISHED bit was not getting set in any nftables code
> paths. It seems that the state was never correctly maintained but there
> was no negative side-effect until commit 41f2c7c342d3 ("net/sched:
> act_ct: Fix promotion of offloaded unreplied tuple") which uses it as
> part of a flow outdated check. The net result is repeated cycles of
> FLOW_CLS_REPLACE / FLOW_CLS_DESTROY commands and never getting any
> FLOW_CLS_STATS commands for a flow.
> 
> This patch sets and clears the NF_FLOW_HW_ESTABLISHED bit for nftables.
> 
> Note that I don't have hardware to test this with. I have observed
> the behaviour and verified the fix with modified veth code.

Very strange, this bit did not exists before:

commit 1a441a9b8be8849957a01413a144f84932c324cb
Author: Vlad Buslov <vladbu@...dia.com>
Date:   Wed Feb 1 17:30:57 2023 +0100

    netfilter: flowtable: cache info of last offload

I have no idea why this is needed.

> Signed-off-by: Donald Hunter <donald.hunter@...il.com>
> Fixes: 41f2c7c342d3 ("net/sched: act_ct: Fix promotion of offloaded unreplied tuple")
> ---
>  net/netfilter/nf_flow_table_offload.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/net/netfilter/nf_flow_table_offload.c b/net/netfilter/nf_flow_table_offload.c
> index 1c26f03fc661..1d017191af80 100644
> --- a/net/netfilter/nf_flow_table_offload.c
> +++ b/net/netfilter/nf_flow_table_offload.c
> @@ -918,6 +918,7 @@ static void flow_offload_work_add(struct flow_offload_work *offload)
>  		goto out;
>  
>  	set_bit(IPS_HW_OFFLOAD_BIT, &offload->flow->ct->status);
> +	set_bit(NF_FLOW_HW_ESTABLISHED, &offload->flow->flags);
>  
>  out:
>  	nf_flow_offload_destroy(flow_rule);
> @@ -925,6 +926,7 @@ static void flow_offload_work_add(struct flow_offload_work *offload)
>  
>  static void flow_offload_work_del(struct flow_offload_work *offload)
>  {
> +	clear_bit(NF_FLOW_HW_ESTABLISHED, &offload->flow->flags);
>  	clear_bit(IPS_HW_OFFLOAD_BIT, &offload->flow->ct->status);
>  	flow_offload_tuple_del(offload, FLOW_OFFLOAD_DIR_ORIGINAL);
>  	if (test_bit(NF_FLOW_HW_BIDIRECTIONAL, &offload->flow->flags))
> -- 
> 2.41.0
>