netdev - Re: [PATCH ipsec 2/3] Revert "xfrm: Remove unneeded device check from validate_xmit

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Message-ID: <aInzWYscMcTRylVg@krikkit>
Date: Wed, 30 Jul 2025 12:26:33 +0200
From: Sabrina Dubroca <sd@...asysnail.net>
To: Cosmin Ratiu <cratiu@...dia.com>
Cc: "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Leon Romanovsky <leonro@...dia.com>,
	"razor@...ckwall.org" <razor@...ckwall.org>,
	"steffen.klassert@...unet.com" <steffen.klassert@...unet.com>
Subject: Re: [PATCH ipsec 2/3] Revert "xfrm: Remove unneeded device check
 from validate_xmit_xfrm"

2025-07-29, 15:27:39 +0000, Cosmin Ratiu wrote:
> On Mon, 2025-07-28 at 17:17 +0200, Sabrina Dubroca wrote:
> > This reverts commit d53dda291bbd993a29b84d358d282076e3d01506.
> > 
> > This change causes traffic using GSO with SW crypto running through a
> > NIC capable of HW offload to no longer get segmented during
> > validate_xmit_xfrm.
> > 
> > Fixes: d53dda291bbd ("xfrm: Remove unneeded device check from
> > validate_xmit_xfrm")
> > 
> 
> Thanks for the fix, but I'm curious about details.
> 
> In that commit, I tried to map all of the possible code paths. Can you
> please explain what code paths I missed that need real_dev given that
> only bonding should use it now?

After running some more tests, it's not about real_dev, it's the other
check ("unlikely(x->xso.dev != dev)" below) that you also removed in
that patch that causes the issue in my setup. I don't know how you
decided that it should be dropped, since it predates bonding's ipsec
offload.
The codepath is the usual:
__dev_queue_xmit -> validate_xmit_skb -> validate_xmit_xfrm

Since the commit message made the incorrect claim "ESP offload off:
validate_xmit_xfrm returns early on !xo." I didn't check if a partial
revert was enough to fix the issue. My bad.

-- 
Sabrina