Subject: Re: [PATCH v8 net-next 05/12] net: dsa: propagate the locked flag down through the DSA layer

From: Ido Schimmel <[email-masked]>
Date: Thu, 20 Oct 2022 16:24:16 +0300

On Thu, Oct 20, 2022 at 04:02:24PM +0300, Vladimir Oltean wrote:
> On Tue, Oct 18, 2022 at 06:56:12PM +0200, Hans J. Schultz wrote:
> > @@ -3315,6 +3316,7 @@ static int dsa_slave_fdb_event(struct net_device *dev,
> >  	struct dsa_port *dp = dsa_slave_to_port(dev);
> >  	bool host_addr = fdb_info->is_local;
> >  	struct dsa_switch *ds = dp->ds;
> > +	u16 fdb_flags = 0;
> >  
> >  	if (ctx && ctx != dp)
> >  		return 0;
> > @@ -3361,6 +3363,9 @@ static int dsa_slave_fdb_event(struct net_device *dev,
> >  		   orig_dev->name, fdb_info->addr, fdb_info->vid,
> >  		   host_addr ? " as host address" : "");
> >  
> > +	if (fdb_info->locked)
> > +		fdb_flags |= DSA_FDB_FLAG_LOCKED;
> 
> This is the bridge->driver direction. In which of the changes up until
> now/through which mechanism will the bridge emit a
> SWITCHDEV_FDB_ADD_TO_DEVICE with fdb_info->locked = true?

I believe it can happen in the following call chain:

br_handle_frame_finish
   br_fdb_update // p->flags & BR_PORT_MAB
       fdb_notify
           br_switchdev_fdb_notify

This can happen with Spectrum when a packet ingresses via a locked port
and incurs an FDB miss in hardware. The packet will be trapped and
injected to the Rx path where it should invoke the above call chain.

> Don't the other switchdev drivers except DSA (search for SWITCHDEV_FDB_EVENT_TO_DEVICE
> in the drivers/ folder) need to handle this new flag too, even if to reject it?

Yes, agree. At least with mlxsw it is not a big deal right now because
it ignores entries with !BR_FDB_ADDED_BY_USER and locked entries are
always like that, but it would be good to make it more explicit.

> 
> When other drivers will want to look at fdb_info->locked, they'll have
> the surprise that it's impossible to maintain backwards compatibility,
> because they didn't use to treat the flag at all in the past (so either
> locked or unlocked, they did the same thing).
> 
> > +
> >  	INIT_WORK(&switchdev_work->work, dsa_slave_switchdev_event_work);
> >  	switchdev_work->event = event;
> >  	switchdev_work->dev = dev;
> > @@ -3369,6 +3374,7 @@ static int dsa_slave_fdb_event(struct net_device *dev,
> >  	ether_addr_copy(switchdev_work->addr, fdb_info->addr);
> >  	switchdev_work->vid = fdb_info->vid;
> >  	switchdev_work->host_addr = host_addr;
> > +	switchdev_work->fdb_flags = fdb_flags;