netdev - Re: [PATCH net-next v3 4/4] net: lan966x: Add ptp trap rules

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Date:   Fri, 9 Dec 2022 17:27:13 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Horatiu Vultur <horatiu.vultur@...rochip.com>
Cc:     Michael Walle <michael@...le.cc>, Steen.Hegelund@...rochip.com,
        UNGLinuxDriver@...rochip.com, daniel.machon@...rochip.com,
        davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        lars.povlsen@...rochip.com, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        pabeni@...hat.com, richardcochran@...il.com
Subject: Re: [PATCH net-next v3 4/4] net: lan966x: Add ptp trap rules

On Fri, Dec 09, 2022 at 04:30:10PM +0100, Horatiu Vultur wrote:
> For example this rule:
> tc filter add dev eth0 ingress chain 8000000 prio 1 handle 1 protocol all
> flower skip_sw dst_mac 00:11:22:33:44:55/ff:ff:ff:ff:ff:ff action trap
> action goto chain 8100000
> 
> This will not be hit until you add this rule:
> tc filter add dev eth0 ingress prio 1 handle 2 matchall skip_sw action goto chain 8000000
> 
> Because this rule will enable the HW. Just to aligned to a SW
> implementation of the tc, we don't enable the vcap until there is a rule
> in chain 0 that has an action to go to chain 8000000 were it resides
> IS2 rules.
> 
> So for example, on a fresh started lan966x the user will add the following
> rule:
> tc filter add dev eth0 ingress chain 8000000 prio 1 handle 1 protocol
> all flower skip_sw dst_mac 00:11:22:33:44:55/ff:ff:ff:ff:ff:ff action
> trap action goto chain 8100000
> 
> He expects this rule not to be hit as there is no rule in chain 0. Now if
> PTP is started and it would enable vcap, then suddenly this rule may be
> hit.

Is it too restrictive to only allow adding offloaded filters to a chain
that has a valid goto towards it, coming (perhaps indirectly) from chain 0?