netdev - Re: [PATCH net-next] net: ocelot: Extend MRP

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Date:   Thu, 11 Mar 2021 20:02:30 +0000
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     Horatiu Vultur <horatiu.vultur@...rochip.com>
CC:     Vladimir Oltean <olteanv@...il.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>,
        Claudiu Manoil <claudiu.manoil@....com>,
        "alexandre.belloni@...tlin.com" <alexandre.belloni@...tlin.com>,
        "UNGLinuxDriver@...rochip.com" <UNGLinuxDriver@...rochip.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next] net: ocelot: Extend MRP

On Thu, Mar 11, 2021 at 08:30:08PM +0100, Horatiu Vultur wrote:
> > > +static void ocelot_mrp_save_mac(struct ocelot *ocelot,
> > > +                             struct ocelot_port *port)
> > > +{
> > > +     ocelot_mact_learn(ocelot, PGID_MRP, mrp_test_dmac,
> > > +                       port->pvid_vlan.vid, ENTRYTYPE_LOCKED);
> > > +     ocelot_mact_learn(ocelot, PGID_MRP, mrp_control_dmac,
> > > +                       port->pvid_vlan.vid, ENTRYTYPE_LOCKED);
> >
> > Let me make sure I understand.
> > By learning these multicast addresses, you mark them as 'not unknown' in
> > the MAC table, because otherwise they will be flooded, including to the
> > CPU port module, and there's no way you can remove the CPU from the
> > flood mask, even if the packets get later redirected through VCAP IS2?
>
> Yes, so far you are right.
>
> > I mean that's the reason why we have the policer on the CPU port for the
> > drop action in ocelot_vcap_init, no?
>
> I am not sure that would work because I want the action to be redirect
> and not policy. Or maybe I am missing something?

Yes, it is not the same context as for tc-drop. The problem for tc-drop
was that the packets would get removed from the hardware datapath, but
they would still get copied to the CPU nonetheless. A policer there was
an OK solution because we wanted to kill those packets completely. Here,
the problem is the same, but we cannot use the same solution, since a
policer will also prevent the frames from being redirected.

> >
> > > diff --git a/include/soc/mscc/ocelot.h b/include/soc/mscc/ocelot.h
> > > index 425ff29d9389..c41696d2e82b 100644
> > > --- a/include/soc/mscc/ocelot.h
> > > +++ b/include/soc/mscc/ocelot.h
> > > @@ -51,6 +51,7 @@
> > >   */
> > >
> > >  /* Reserve some destination PGIDs at the end of the range:
> > > + * PGID_MRP: used for not flooding MRP frames to CPU
> >
> > Could this be named PGID_BLACKHOLE or something? It isn't specific to
> > MRP if I understand correctly. We should also probably initialize it
> > with zero.
>
> It shouldn't matter the value, what is important that the CPU port not
> to be set. Because the value of this PGID will not be used in the
> fowarding decision.
> Currently only MRP is using it so that is the reason for naming it like
> that but I can rename it and initialized it to 0 to be more clear.

So tell me more about this behavior.
Is there no way to suppress the flooding to CPU action, even if the
frame was hit by a TCAM rule? Let's forget about MRP, assume this is an
broadcast IPv4 packet, and we have a matching src_ip rule to perform
mirred egress redirect to another port.
Would the CPU be flooded with this traffic too? What would you do to
avoid that situation?