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

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Message-ID: <20241219145229.2uy3d3pnjqmimq66@skbuf>
Date: Thu, 19 Dec 2024 16:52:29 +0200
From: Vladimir Oltean <olteanv@...il.com>
To: Tobias Waldekranz <tobias@...dekranz.com>
Cc: davem@...emloft.net, kuba@...nel.org, andrew@...n.ch,
	f.fainelli@...il.com, netdev@...r.kernel.org, linux@...linux.org.uk,
	chris.packham@...iedtelesis.co.nz, pabeni@...hat.com
Subject: Re: [PATCH v2 net 4/4] net: dsa: mv88e6xxx: Limit rsvd2cpu policy to
 user ports on 6393X

On Thu, Dec 19, 2024 at 04:42:08PM +0200, Vladimir Oltean wrote:
> The other driver with tx_fwd_offload, sja1105,

Correction: I forgot there is one more driver with tx_fwd_offload:
vsc73xx, but that doesn't properly support link-local traffic yet at all,
according to the vsc73xx_port_stp_state_set() comment. So we can ignore it.

> is going to drop any
> packet coming from the host_port which isn't sent through a management
> route (set up by sja1105_defer_xmit()). So it's more than likely bugged.
> 
> We can't fix this from sja1105_xmit() by reordering sja1105_imprecise_xmit()
> and sja1105_defer_xmit(). It's not just the order of operations in the
> tagger. It's the fact that the bridge thinks it doesn't need to clone
> the skb, and it does.

Another correction: we could probably make a best-effort attempt to
honor skb->offload_fwd_mark in sja1105_mgmt_xmit() by setting mgmt_route.destports
to the bit mask of all other ports that are in dsa_port_bridge_dev_get(dp).
But it gets unpleasantly difficult to manage, plus I think we still don't
get MAC SA learning from these packets.

> So yes, it's probably best to exclude link-local from skb->offload_fwd_mark.

So I'm still of this opinion :) I think the effort to handle the corner
cases isn't worth it relative to the benefit of offloading the forwarding
of slow protocols.