Re: [PATCH nf-next v3 2/3] netfilter: flowtable: carry a priority into the offload

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

On Sun, Oct 04, 2026 at 07:16:35PM +0200, Julius Bairaktaris wrote:
> Packets forwarded by the flowtable skip the ruleset, so a priority set
> by "meta priority set" before "flow add" only applies to the first
> packets of a connection, and drivers never see it.
> 
> Store skb->priority of the packet that creates the flow, apply it in
> the software fast path and emit it as FLOW_ACTION_PRIORITY, the action
> act_skbedit uses. Flows without a priority are unchanged. On IPv4,
> ip_forward() derives a priority from the TOS by default, so a flow can
> carry one without a rule. The priority applies to both directions.
> 
> airoha uses it as the QoS queue of flows that leave through a GDM port,
> as its software path does, mtk ignores it like FLOW_ACTION_CSUM, and
> mlx5 ignores it on flowtable flows (previous patch). airoha and mtk
> parse tc flower rules in the same function, so they now also accept
> skbedit priority there.

I think we already mentioned this only works for hardware, this is a
no-go.

> Assisted-by: Claude:claude-opus-5
> Signed-off-by: Julius Bairaktaris <julius@bairaktaris.de>
> ---
>  Documentation/networking/nf_flowtable.rst       |  4 +++-
>  drivers/net/ethernet/airoha/airoha_ppe.c        |  3 +++
>  drivers/net/ethernet/mediatek/mtk_ppe_offload.c |  1 +
>  include/net/netfilter/nf_flow_table.h           |  1 +
>  net/netfilter/nf_flow_table_ip.c                |  6 ++++++
>  net/netfilter/nf_flow_table_offload.c           | 11 +++++++++++
>  net/netfilter/nft_flow_offload.c                |  2 ++
>  7 files changed, 27 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/networking/nf_flowtable.rst b/Documentation/networking/nf_flowtable.rst
> index d757c21c10f2..5844ab19aec6 100644
> --- a/Documentation/networking/nf_flowtable.rst
> +++ b/Documentation/networking/nf_flowtable.rst
> @@ -71,7 +71,9 @@ forwarding path including the Netfilter hooks and the flowtable fastpath bypass.
>  
>  The flowtable entry also stores the NAT configuration, so all packets are
>  mangled according to the NAT policy that is specified from the classic IP
> -forwarding path. The TTL is decremented before calling neigh_xmit(). Fragmented
> +forwarding path. The TTL is decremented before calling neigh_xmit(). The flow
> +also stores the priority of the packet that created it, so a priority set before
> +``flow add`` applies to the packets that the flowtable forwards. Fragmented
>  traffic is passed up to follow the classic IP forwarding path given that the
>  transport header is missing, in this case, flowtable lookups are not possible.
>  TCP RST and FIN packets are also passed up to the classic IP forwarding path to
> diff --git a/drivers/net/ethernet/airoha/airoha_ppe.c b/drivers/net/ethernet/airoha/airoha_ppe.c
> index 92611802801e..e790305ea955 100644
> --- a/drivers/net/ethernet/airoha/airoha_ppe.c
> +++ b/drivers/net/ethernet/airoha/airoha_ppe.c
> @@ -1161,6 +1161,9 @@ static int airoha_ppe_flow_offload_replace(struct airoha_eth *eth,
>  		case FLOW_ACTION_REDIRECT:
>  			odev = act->dev;
>  			break;
> +		case FLOW_ACTION_PRIORITY:
> +			priority = act->priority;
> +			break;
>  		case FLOW_ACTION_CSUM:
>  			break;
>  		case FLOW_ACTION_VLAN_PUSH:
> diff --git a/drivers/net/ethernet/mediatek/mtk_ppe_offload.c b/drivers/net/ethernet/mediatek/mtk_ppe_offload.c
> index 99b28aaa7cc4..4ee99e8e4a34 100644
> --- a/drivers/net/ethernet/mediatek/mtk_ppe_offload.c
> +++ b/drivers/net/ethernet/mediatek/mtk_ppe_offload.c
> @@ -378,6 +378,7 @@ mtk_flow_offload_replace(struct mtk_eth *eth, struct flow_cls_offload *f,
>  		case FLOW_ACTION_REDIRECT:
>  			odev = act->dev;
>  			break;
> +		case FLOW_ACTION_PRIORITY:
>  		case FLOW_ACTION_CSUM:
>  			break;
>  		case FLOW_ACTION_VLAN_PUSH:
> diff --git a/include/net/netfilter/nf_flow_table.h b/include/net/netfilter/nf_flow_table.h
> index f2e2771f188f..23218c8cbc3d 100644
> --- a/include/net/netfilter/nf_flow_table.h
> +++ b/include/net/netfilter/nf_flow_table.h
> @@ -202,6 +202,7 @@ struct flow_offload {
>  	unsigned long				flags;
>  	u16					type;
>  	u32					timeout;
> +	u32					priority;
>  	struct rcu_head				rcu_head;
>  };
>  
> diff --git a/net/netfilter/nf_flow_table_ip.c b/net/netfilter/nf_flow_table_ip.c
> index c8c29a9a1684..c85e2d608c32 100644
> --- a/net/netfilter/nf_flow_table_ip.c
> +++ b/net/netfilter/nf_flow_table_ip.c
> @@ -509,6 +509,9 @@ static int nf_flow_offload_forward(struct nf_flowtable_ctx *ctx,
>  	ip_decrease_ttl(iph);
>  	skb_clear_tstamp(skb);
>  
> +	if (flow->priority)
> +		skb->priority = flow->priority;
> +
>  	if (flow_table->flags & NF_FLOWTABLE_COUNTER)
>  		nf_ct_acct_update(flow->ct, tuplehash->tuple.dir, skb->len);
>  
> @@ -1104,6 +1107,9 @@ static int nf_flow_offload_ipv6_forward(struct nf_flowtable_ctx *ctx,
>  	ip6h->hop_limit--;
>  	skb_clear_tstamp(skb);
>  
> +	if (flow->priority)
> +		skb->priority = flow->priority;
> +
>  	if (flow_table->flags & NF_FLOWTABLE_COUNTER)
>  		nf_ct_acct_update(flow->ct, tuplehash->tuple.dir, skb->len);
>  
> diff --git a/net/netfilter/nf_flow_table_offload.c b/net/netfilter/nf_flow_table_offload.c
> index 801a3dd9ceea..caaadffc2563 100644
> --- a/net/netfilter/nf_flow_table_offload.c
> +++ b/net/netfilter/nf_flow_table_offload.c
> @@ -696,6 +696,17 @@ nf_flow_rule_route_common(struct net *net, const struct flow_offload *flow,
>  	    flow_offload_eth_dst(net, flow, dir, flow_rule) < 0)
>  		return -1;
>  
> +	if (flow->priority) {
> +		struct flow_action_entry *entry;
> +
> +		entry = flow_action_entry_next(flow_rule);
> +		if (!entry)
> +			return -1;
> +
> +		entry->id = FLOW_ACTION_PRIORITY;
> +		entry->priority = flow->priority;
> +	}
> +
>  	tuple = &flow->tuplehash[dir].tuple;
>  
>  	for (i = 0; i < tuple->encap_num; i++) {
> diff --git a/net/netfilter/nft_flow_offload.c b/net/netfilter/nft_flow_offload.c
> index 32b4281038dd..c8eaf7bc356d 100644
> --- a/net/netfilter/nft_flow_offload.c
> +++ b/net/netfilter/nft_flow_offload.c
> @@ -117,6 +117,8 @@ static void nft_flow_offload_eval(const struct nft_expr *expr,
>  	if (tcph)
>  		flow_offload_ct_tcp(ct);
>  
> +	flow->priority = pkt->skb->priority;
> +
>  	__set_bit(NF_FLOW_HW_BIDIRECTIONAL, &flow->flags);
>  	ret = flow_offload_add(flowtable, flow);
>  	if (ret < 0)
> -- 
> 2.53.0
> 
>