Linux Ethernet Bridging - Jul 2022 - [Bridge] [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 at kapio-technology.com
wrote:
> On 2022-07-17 14:57, Vladimir Oltean wrote:
> > On Sun, Jul 17, 2022 at 02:21:47PM +0200, netdev at
kapio-technology.com
> > wrote:
> > > On 2022-07-13 14:39, Ido Schimmel wrote:
> > > > On Wed, Jul 13, 2022 at 09:09:58AM +0200, netdev at
kapio-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.

On 2022-07-17 15:59, Vladimir Oltean wrote:
> On Sun, Jul 17, 2022 at 03:09:10PM +0200, netdev at kapio-technology.com 
> wrote:
>> On 2022-07-17 14:57, Vladimir Oltean wrote:
>> > On Sun, Jul 17, 2022 at 02:21:47PM +0200, netdev at
kapio-technology.com
>> > wrote:
>> > > On 2022-07-13 14:39, Ido Schimmel wrote:
>> > > > On Wed, Jul 13, 2022 at 09:09:58AM +0200, netdev at
kapio-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.