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: <20250716042722.GA12760@system.software.com>
Date: Wed, 16 Jul 2025 13:27:22 +0900
From: Byungchul Park <byungchul@...com>
To: Pavel Begunkov <asml.silence@...il.com>
Cc: Mina Almasry <almasrymina@...gle.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 11:37:45AM +0100, Pavel Begunkov 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

That's whay I'd been keeping the patch, 'netmem: remove __netmem_get_pp()'
until v6 [1].

[1] https://lore.kernel.org/all/20250620041224.46646-7-byungchul@sk.com/

However, as the following change log described [2], I excluded the patch
from v7 since __netmem_get_pp() started to be used again by libeth.

[2] https://lore.kernel.org/all/20250625043350.7939-1-byungchul@sk.com/

> 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.

Killing __netmem_get_pp() would be the best I think.

	Byungchul
> 
> 
> > We could have an unsafe version of netmem_to_nmdesc which converts the
> > netmem to netmem_desc without clearing the lsb and mark it unsafe.
> > 
> 
> --
> Pavel Begunkov