netdev - 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 15:57:18 +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 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.