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

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Message-ID: <e1c1e7c114f0226b116d9549cea8e7a9@kapio-technology.com>
Date:   Sun, 17 Jul 2022 16:57:50 +0200
From:   netdev@...io-technology.com
To:     Vladimir Oltean <olteanv@...il.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 2022-07-17 15:59, Vladimir Oltean wrote:
> 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.

Maybe I am just trying to understand the problem you are posing, so 
afaics MAC addresses should be unique and having the same MAC address 
behind a locked port and a not-locked port seems like a 
mis-configuration regardless of vlan setup? As the zero-DPV entry only 
blocks the specific SA MAC on a specific vlan, which is behind a locked 
port, there shouldn't be any problem...?

If the host behind a locked port starts sending on another vlan than 
where it got the first locked entry, another locked entry will occur, as 
the locked entries are MAC + vlan.

> 
>> 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.