linux-kernel - Re: [PATCH v4 net-next 3/6] drivers: net: dsa: add locked fdb entry flag to drivers

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Date:   Sun, 17 Jul 2022 16:59:51 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     netdev@...io-technology.com
Cc:     Ido Schimmel <idosch@...dia.com>, davem@...emloft.net,
        kuba@...nel.org, netdev@...r.kernel.org,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>, Jiri Pirko <jiri@...nulli.us>,
        Ivan Vecera <ivecera@...hat.com>,
        Roopa Prabhu <roopa@...dia.com>,
        Nikolay Aleksandrov <razor@...ckwall.org>,
        Shuah Khan <shuah@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        linux-kernel@...r.kernel.org, bridge@...ts.linux-foundation.org,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v4 net-next 3/6] drivers: net: dsa: add locked fdb entry
 flag to drivers

On Sun, Jul 17, 2022 at 03:09:10PM +0200, netdev@...io-technology.com wrote:
> On 2022-07-17 14:57, Vladimir Oltean wrote:
> > On Sun, Jul 17, 2022 at 02:21:47PM +0200, netdev@...io-technology.com
> > wrote:
> > > On 2022-07-13 14:39, Ido Schimmel wrote:
> > > > On Wed, Jul 13, 2022 at 09:09:58AM +0200, netdev@...io-technology.com
> > > > wrote:
> > > 
> > > >
> > > > What are "Storm Prevention" and "zero-DPV" FDB entries?
> > > 
> > > They are both FDB entries that at the HW level drops all packets
> > > having a
> > > specific SA, thus using minimum resources.
> > > (thus the name "Storm Prevention" aka, protection against DOS
> > > attacks. We
> > > must remember that we operate with CPU based learning.)
> > 
> > DPV means Destination Port Vector, and an ATU entry with a DPV of 0
> > essentially means a FDB entry pointing nowhere, so it will drop the
> > packet. That's a slight problem with Hans' implementation, the bridge
> > thinks that the locked FDB entry belongs to port X, but in reality it
> > matches on all bridged ports (since it matches by FID). FID allocation
> > in mv88e6xxx is slightly strange, all VLAN-unaware bridge ports,
> > belonging to any bridge, share the same FID, so the FDB databases are
> > not exactly isolated from each other.
> 
> But if the locked port is vlan aware and has a pvid, it should not block
> other ports.

I don't understand what you want to say by that. It will block all other
packets with the same MAC SA that are classified to the same FID.
In case of VLAN-aware bridges, the mv88e6xxx driver allocates a new FID
for each VID (see mv88e6xxx_atu_new). In other words, if a locked port
is VLAN-aware and has a pvid, then whatever the PVID may be, all ports
in that same VLAN are still blocked in the same way.

> Besides the fid will be zero with vlan unaware afaik, and all with
> zero fid do not create locked entries.

If by 0 you mean 1 (MV88E6XXX_FID_BRIDGED), then you are correct: ports
with FID 0 (MV88E6XXX_FID_STANDALONE) should not create locked FDB
entries, because they are, well, standalone and not bridged.
Again I don't exactly see the relevance though.