netdev - Re: [PATCH net v2] xdp: update mem type when page pool is used for generic XDP

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Message-ID: <aN51q5TeJV5R5x04@boxer>
Date: Thu, 2 Oct 2025 14:54:20 +0200
From: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
To: Octavian Purdila <tavip@...gle.com>
CC: Jakub Kicinski <kuba@...nel.org>, <davem@...emloft.net>,
	<edumazet@...gle.com>, <pabeni@...hat.com>, <horms@...nel.org>,
	<ast@...nel.org>, <daniel@...earbox.net>, <hawk@...nel.org>,
	<john.fastabend@...il.com>, <sdf@...ichev.me>, <kuniyu@...gle.com>,
	<aleksander.lobakin@...el.com>, <toke@...hat.com>, <lorenzo@...nel.org>,
	<netdev@...r.kernel.org>, <bpf@...r.kernel.org>,
	<syzbot+ff145014d6b0ce64a173@...kaller.appspotmail.com>
Subject: Re: [PATCH net v2] xdp: update mem type when page pool is used for
 generic XDP

On Wed, Oct 01, 2025 at 06:15:25PM -0700, Octavian Purdila wrote:
> On Wed, Oct 1, 2025 at 12:06 PM Maciej Fijalkowski
> <maciej.fijalkowski@...el.com> wrote:
> >
> > On Wed, Oct 01, 2025 at 08:27:37AM -0700, Jakub Kicinski wrote:
> > > On Wed, 1 Oct 2025 16:42:29 +0200 Maciej Fijalkowski wrote:
> > > > Here we piggy back on sk_buff::pp_recycle setting as it implies underlying
> > > > memory is backed by page pool.
> > >
> > > skb->pp_recycle means that if the pages of the skb came from a pp then
> > > the skb is holding a pp reference not a full page reference on those
> > > pages. It does not mean that all pages of an skb came from pp.
> > > In practice it may be equivalent, especially here. But I'm slightly
> > > worried that checking pp_recycle will lead to confusion..
> >
> > Mmm ok - maybe that's safer and straight-forward?
> >
> > diff --git a/net/core/dev.c b/net/core/dev.c
> > index 93a25d87b86b..7707a95ca8ed 100644
> > --- a/net/core/dev.c
> > +++ b/net/core/dev.c
> > @@ -5269,6 +5269,9 @@ u32 bpf_prog_run_generic_xdp(struct sk_buff *skb, struct xdp_buff *xdp,
> >         orig_bcast = is_multicast_ether_addr_64bits(eth->h_dest);
> >         orig_eth_type = eth->h_proto;
> >
> > +       xdp->rxq->mem.type = page_pool_page_is_pp(virt_to_page(xdp->data)) ?
> > +               MEM_TYPE_PAGE_POOL : MEM_TYPE_PAGE_SHARED;
> > +
> >         act = bpf_prog_run_xdp(xdp_prog, xdp);
> >
> >         /* check if bpf_xdp_adjust_head was used */
> >
> > As you know we do not have that kind of granularity within xdp_buff where
> > we could distinguish the memory provider per linear part and each frag...
> 
> LGTM, based on my limited understanding. I can also confirm the syz
> repro no longer crashes with this patch.

Would you be OK with me submitting this fix and giving you the proper
credit?