Re: [PATCH v2 net 4/4] net: dsa: mv88e6xxx: Limit rsvd2cpu policy to user ports on 6393X

[Vladimir Oltean <olteanv@gmail.com>]

On Thu, Dec 19, 2024 at 01:30:43PM +0100, Tobias Waldekranz wrote:
> For packets with a DA in the IEEE reserved L2 group range, originating
> from a CPU, forward it as normal, rather than classifying it as
> management.

Doesn't this break STP? Must be able to inject into ports with an STP
state other than FORWARDING. I expect that you need a DSA_CMD_FROM_CPU
tag for that, can't do it with DSA_CMD_FORWARD.

> Example use-case:
> 
>      bridge (group_fwd_mask 0x4000)
>      / |  \
>  swp1 swp2 tap0
>    \   /
> (mv88e6xxx)
> 
> We've created a bridge with a non-zero group_fwd_mask (allowing LLDP
> in this example) containing a set of ports managed by mv88e6xxx and
> some foreign interface (e.g. an L2 VPN tunnel).
> 
> Since an LLDP packet coming in to the bridge from the other side of
> tap0 is eligable for tx forward offloading, a FORWARD frame destined
> for swp1 and swp2 would be send to the conduit interface.
> 
> Before this change, due to rsvd2cpu being enabled on the CPU port, the
> switch would try to trap it back to the CPU. Given that the CPU is
> trusted, instead assume that it indeed meant for the packet to be
> forwarded like any other.

It looks like an oversight in the switchdev tx_fwd_offload scheme. Can't
we teach nbp_switchdev_frame_mark_tx_fwd_offload() to make an exception
for is_link_local_ether_addr() packets, and not set skb->offload_fwd_mark?