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

[netdev]

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