netdev - Re: [PATCH net-next ct-offload 03/13] net/sched: act_ct: Support restoring conntrack info on skbs

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Date:   Fri, 6 Mar 2020 13:16:39 +0000
From:   Edward Cree <ecree@...arflare.com>
To:     Paul Blakey <paulb@...lanox.com>,
        Saeed Mahameed <saeedm@...lanox.com>,
        "Oz Shlomo" <ozsh@...lanox.com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Vlad Buslov <vladbu@...lanox.com>,
        David Miller <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Jiri Pirko <jiri@...lanox.com>, Roi Dayan <roid@...lanox.com>
Subject: Re: [PATCH net-next ct-offload 03/13] net/sched: act_ct: Support
 restoring conntrack info on skbs

On 05/03/2020 15:34, Paul Blakey wrote:
> Provide an API to restore the ct state pointer.
>
> This may be used by drivers to restore the ct state if they
> miss in tc chain after they already did the hardware connection
> tracking action (ct_metadata action).
>
> For example, consider the following rule on chain 0 that is in_hw,
> however chain 1 is not_in_hw:
>
> $ tc filter add dev ... chain 0 ... \
>   flower ... action ct pipe action goto chain 1
>
> Packets of a flow offloaded (via nf flow table offload) by the driver
> hit this rule in hardware, will be marked with the ct metadata action
> (mark, label, zone) that does the equivalent of the software ct action,
> and when the packet jumps to hardware chain 1, there would be a miss.
>
> CT was already processed in hardware. Therefore, the driver's miss
> handling should restore the ct state on the skb, using the provided API,
> and continue the packet processing in chain 1.
IMNSHO this demonstrates why hardware should do all-or-nothingoffload,
 in the cases where it can't perform the whole filtering it should
 provide the unmodified packet so that SW can start over from a clean
 state.
But as long as these epicycles don't affect drivers for such HW, I guess
 I can't object too hard to them being added.