netdev - Re: [PATCH net-next v8 0/7] net/sched: cls_api: Support hardware miss to tc action

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Date:   Mon, 6 Feb 2023 13:34:25 +0100
From:   Ilya Maximets <i.maximets@....org>
To:     Paul Blakey <paulb@...dia.com>, netdev@...r.kernel.org,
        Saeed Mahameed <saeedm@...dia.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        "David S. Miller" <davem@...emloft.net>
Cc:     Oz Shlomo <ozsh@...dia.com>, Jiri Pirko <jiri@...dia.com>,
        Roi Dayan <roid@...dia.com>, Vlad Buslov <vladbu@...dia.com>,
        Marcelo Leitner <mleitner@...hat.com>, i.maximets@....org
Subject: Re: [PATCH net-next v8 0/7] net/sched: cls_api: Support hardware miss
 to tc action

On 2/5/23 16:49, Paul Blakey wrote:
> Hi,
> 
> This series adds support for hardware miss to instruct tc to continue execution
> in a specific tc action instance on a filter's action list. The mlx5 driver patch
> (besides the refactors) shows its usage instead of using just chain restore.
> 
> Currently a filter's action list must be executed all together or
> not at all as driver are only able to tell tc to continue executing from a
> specific tc chain, and not a specific filter/action.
> 
> This is troublesome with regards to action CT, where new connections should
> be sent to software (via tc chain restore), and established connections can
> be handled in hardware.
> 
> Checking for new connections is done when executing the ct action in hardware
> (by checking the packet's tuple against known established tuples).
> But if there is a packet modification (pedit) action before action CT and the
> checked tuple is a new connection, hardware will need to revert the previous
> packet modifications before sending it back to software so it can
> re-match the same tc filter in software and re-execute its CT action.
> 
> The following is an example configuration of stateless nat
> on mlx5 driver that isn't supported before this patchet:
> 
>  #Setup corrosponding mlx5 VFs in namespaces
>  $ ip netns add ns0
>  $ ip netns add ns1
>  $ ip link set dev enp8s0f0v0 netns ns0
>  $ ip netns exec ns0 ifconfig enp8s0f0v0 1.1.1.1/24 up
>  $ ip link set dev enp8s0f0v1 netns ns1
>  $ ip netns exec ns1 ifconfig enp8s0f0v1 1.1.1.2/24 up
> 
>  #Setup tc arp and ct rules on mxl5 VF representors
>  $ tc qdisc add dev enp8s0f0_0 ingress
>  $ tc qdisc add dev enp8s0f0_1 ingress
>  $ ifconfig enp8s0f0_0 up
>  $ ifconfig enp8s0f0_1 up
> 
>  #Original side
>  $ tc filter add dev enp8s0f0_0 ingress chain 0 proto ip flower \
>     ct_state -trk ip_proto tcp dst_port 8888 \
>       action pedit ex munge tcp dport set 5001 pipe \
>       action csum ip tcp pipe \
>       action ct pipe \
>       action goto chain 1
>  $ tc filter add dev enp8s0f0_0 ingress chain 1 proto ip flower \
>     ct_state +trk+est \
>       action mirred egress redirect dev enp8s0f0_1
>  $ tc filter add dev enp8s0f0_0 ingress chain 1 proto ip flower \
>     ct_state +trk+new \
>       action ct commit pipe \
>       action mirred egress redirect dev enp8s0f0_1
>  $ tc filter add dev enp8s0f0_0 ingress chain 0 proto arp flower \
>       action mirred egress redirect dev enp8s0f0_1
> 
>  #Reply side
>  $ tc filter add dev enp8s0f0_1 ingress chain 0 proto arp flower \
>       action mirred egress redirect dev enp8s0f0_0
>  $ tc filter add dev enp8s0f0_1 ingress chain 0 proto ip flower \
>     ct_state -trk ip_proto tcp \ 
>       action ct pipe \
>       action pedit ex munge tcp sport set 8888 pipe \
>       action csum ip tcp pipe \
>       action mirred egress redirect dev enp8s0f0_0
> 
>  #Run traffic
>  $ ip netns exec ns1 iperf -s -p 5001&
>  $ sleep 2 #wait for iperf to fully open
>  $ ip netns exec ns0 iperf -c 1.1.1.2 -p 8888
> 
>  #dump tc filter stats on enp8s0f0_0 chain 0 rule and see hardware packets:
>  $ tc -s filter show dev enp8s0f0_0 ingress chain 0 proto ip | grep "hardware.*pkt"
>         Sent hardware 9310116832 bytes 6149672 pkt
>         Sent hardware 9310116832 bytes 6149672 pkt
>         Sent hardware 9310116832 bytes 6149672 pkt
> 
> A new connection executing the first filter in hardware will first rewrite
> the dst port to the new port, and then the ct action is executed,
> because this is a new connection, hardware will need to be send this back
> to software, on chain 0, to execute the first filter again in software.
> The dst port needs to be reverted otherwise it won't re-match the old
> dst port in the first filter. Because of that, currently mlx5 driver will
> reject offloading the above action ct rule.
> 
> This series adds supports partial offload of a filter's action list,
> and letting tc software continue processing in the specific action instance
> where hardware left off (in the above case after the "action pedit ex munge tcp
> dport... of the first rule") allowing support for scenarios such as the above.


Hi, Paul.  Not sure if this was discussed before, but don't we also need
a new TCA_CLS_FLAGS_IN_HW_PARTIAL flag or something like this?

Currently the in_hw/not_in_hw flags are reported per filter, i.e. these
flags are not per-action.  This may cause confusion among users, if flows
are reported as in_hw, while they are actually partially or even mostly
processed in SW.

What do you think?

Best regards, Ilya Maximets.