netdev - Re: [PATCH v5 bpf 1/2] xdp: introduce xdp_convert_skb_to

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Message-ID: <aQidBn22H1UVxST5@boxer>
Date: Mon, 3 Nov 2025 13:16:06 +0100
From: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
To: Jakub Kicinski <kuba@...nel.org>
CC: <bpf@...r.kernel.org>, <ast@...nel.org>, <daniel@...earbox.net>,
	<hawk@...nel.org>, <netdev@...r.kernel.org>, <magnus.karlsson@...el.com>,
	<aleksander.lobakin@...el.com>, <ilias.apalodimas@...aro.org>,
	<toke@...hat.com>, <lorenzo@...nel.org>,
	<syzbot+ff145014d6b0ce64a173@...kaller.appspotmail.com>, Ihor Solodrai
	<ihor.solodrai@...ux.dev>, Octavian Purdila <tavip@...gle.com>
Subject: Re: [PATCH v5 bpf 1/2] xdp: introduce xdp_convert_skb_to_buff()

On Fri, Oct 31, 2025 at 11:49:52AM -0700, Jakub Kicinski wrote:
> On Fri, 31 Oct 2025 12:37:37 +0100 Maciej Fijalkowski wrote:
> > > > would be fine for you? Plus AI reviewer has kicked me in the nuts on veth
> > > > patch so have to send v6 anyways.  
> > > 
> > > The veth side unfortunately needs more work than Mr Robot points out.
> > > For some reason veth tries to turn skb into an xdp_frame..  
> > 
> > That is beyond the scope of the fix that I started doing as you're
> > undermining overall XDP support in veth, IMHO.
> > 
> > I can follow up on this on some undefined future but right now I will
> > have to switch to some other work.
> > 
> > If you disagree and insist on addressing skb->xdp_frame in veth within
> > this patchset then I'm sorry but I will have to postpone my activities
> > here.
> 
> Yeah, I understand. A lot of the skb<>XDP integration is a steaming
> pile IMO, as mentioned elsewhere. I'd like to keep the core clean
> tho, so if there's some corner cases in veth after your changes
> I'll live. But I'm worried that the bugs in veth will make you
> want to preserve the conditional in xdp_convert_skb_to_buff() :(

Probably the conditional would cover these corner cases, but I am not
insisting on it. skb_pp_cow_data() is called under certain circumstances
in veth but I have never seen a case on my side where it was skipped,
mostly because of headroom size being too small.