linux-kernel - Re: [PATCH net-next v10 02/12] netmem: use netmem_desc instead of page to access ->pp in __netmem_get

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAHS8izMYLw3JfonoQ7n4ZaWivdBVKqZejgyRiAku5j1rx7gBPQ@mail.gmail.com>
Date: Tue, 15 Jul 2025 12:06:36 -0700
From: Mina Almasry <almasrymina@...gle.com>
To: Pavel Begunkov <asml.silence@...il.com>
Cc: Byungchul Park <byungchul@...com>, willy@...radead.org, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, kernel_team@...ynix.com, 
	ilias.apalodimas@...aro.org, harry.yoo@...cle.com, akpm@...ux-foundation.org, 
	andrew+netdev@...n.ch, toke@...hat.com, david@...hat.com, 
	Liam.Howlett@...cle.com, vbabka@...e.cz, rppt@...nel.org, surenb@...gle.com, 
	mhocko@...e.com, linux-rdma@...r.kernel.org, bpf@...r.kernel.org, 
	vishal.moola@...il.com, hannes@...xchg.org, ziy@...dia.com, 
	jackmanb@...gle.com, wei.fang@....com, shenwei.wang@....com, 
	xiaoning.wang@....com, davem@...emloft.net, edumazet@...gle.com, 
	kuba@...nel.org, pabeni@...hat.com, anthony.l.nguyen@...el.com, 
	przemyslaw.kitszel@...el.com, sgoutham@...vell.com, gakula@...vell.com, 
	sbhatta@...vell.com, hkelam@...vell.com, bbhushan2@...vell.com, 
	tariqt@...dia.com, ast@...nel.org, daniel@...earbox.net, hawk@...nel.org, 
	john.fastabend@...il.com, sdf@...ichev.me, saeedm@...dia.com, leon@...nel.org, 
	mbloch@...dia.com, danishanwar@...com, rogerq@...nel.org, nbd@....name, 
	lorenzo@...nel.org, ryder.lee@...iatek.com, shayne.chen@...iatek.com, 
	sean.wang@...iatek.com, matthias.bgg@...il.com, 
	angelogioacchino.delregno@...labora.com, aleksander.lobakin@...el.com, 
	horms@...nel.org, m-malladi@...com, krzysztof.kozlowski@...aro.org, 
	matthias.schiffer@...tq-group.com, robh@...nel.org, imx@...ts.linux.dev, 
	intel-wired-lan@...ts.osuosl.org, linux-arm-kernel@...ts.infradead.org, 
	linux-wireless@...r.kernel.org, linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH net-next v10 02/12] netmem: use netmem_desc instead of
 page to access ->pp in __netmem_get_pp()

On Tue, Jul 15, 2025 at 3:36 AM Pavel Begunkov <asml.silence@...il.com> wrote:
>
> On 7/14/25 20:37, Mina Almasry wrote:
> > On Mon, Jul 14, 2025 at 5:01 AM Byungchul Park <byungchul@...com> wrote:
> ...>> +static inline struct netmem_desc *pp_page_to_nmdesc(struct page *page)
> >> +{
> >> +       DEBUG_NET_WARN_ON_ONCE(!page_pool_page_is_pp(page));
> >> +
> >> +       /* XXX: How to extract netmem_desc from page must be changed,
> >> +        * once netmem_desc no longer overlays on page and will be
> >> +        * allocated through slab.
> >> +        */
> >> +       return (struct netmem_desc *)page;
> >> +}
> >> +
> >
> > Same thing. Do not create a generic looking pp_page_to_nmdesc helper
> > which does not check that the page is the correct type. The
> > DEBUG_NET... is not good enough.
> >
> > You don't need to add a generic helper here. There is only one call
> > site. Open code this in the callsite. The one callsite is marked as
> > unsafe, only called by code that knows that the netmem is specifically
> > a pp page. Open code this in the unsafe callsite, instead of creating
> > a generic looking unsafe helper and not even documenting it's unsafe.
> >
> >>   /**
> >>    * __netmem_get_pp - unsafely get pointer to the &page_pool backing @netmem
> >>    * @netmem: netmem reference to get the pointer from
> >> @@ -280,7 +291,7 @@ static inline struct net_iov *__netmem_clear_lsb(netmem_ref netmem)
> >>    */
> >>   static inline struct page_pool *__netmem_get_pp(netmem_ref netmem)
> >>   {
> >> -       return __netmem_to_page(netmem)->pp;
> >> +       return pp_page_to_nmdesc(__netmem_to_page(netmem))->pp;
> >>   }
> >
> > This makes me very sad. Casting from netmem -> page -> nmdesc...
>
> The function is not used, and I don't think the series adds any
> new users? It can be killed then. It's a horrible function anyway,
> would be much better to have a variant taking struct page * if
> necessary.
>
> > Instead, we should be able to go from netmem directly to nmdesc. I
> > would suggest rename __netmem_clear_lsb to netmem_to_nmdesc and have
> > it return netmem_desc instead of net_iov. Then use it here.
>
> Glad you liked the diff I suggested :) In either case, seems
> like it's not strictly necessary for this iteration as
> __netmem_get_pp() should be killed, and the rest of patches work
> directly with pages.

Good catch, in that case lets just delete __netmem_get_pp and there is
no need to add a netmem_nmdesc unless we find some other call site
that needs it.

-- 
Thanks,
Mina