linux-kernel - Re: [PATCH net-next 9/9] page_pool: access ->pp_magic through struct netmem_desc in page_pool_page_is

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: <20250612003949.GA41589@system.software.com>
Date: Thu, 12 Jun 2025 09:39:49 +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, kuba@...nel.org,
	ilias.apalodimas@...aro.org, harry.yoo@...cle.com, hawk@...nel.org,
	akpm@...ux-foundation.org, davem@...emloft.net,
	john.fastabend@...il.com, andrew+netdev@...n.ch, toke@...hat.com,
	tariqt@...dia.com, edumazet@...gle.com, pabeni@...hat.com,
	saeedm@...dia.com, leon@...nel.org, ast@...nel.org,
	daniel@...earbox.net, david@...hat.com, lorenzo.stoakes@...cle.com,
	Liam.Howlett@...cle.com, vbabka@...e.cz, rppt@...nel.org,
	surenb@...gle.com, mhocko@...e.com, horms@...nel.org,
	linux-rdma@...r.kernel.org, bpf@...r.kernel.org,
	vishal.moola@...il.com
Subject: Re: [PATCH net-next 9/9] page_pool: access ->pp_magic through struct
 netmem_desc in page_pool_page_is_pp()

On Wed, Jun 11, 2025 at 03:30:28PM +0100, Pavel Begunkov wrote:
> On 6/10/25 02:45, Byungchul Park wrote:
> > On Mon, Jun 09, 2025 at 10:39:06AM -0700, Mina Almasry wrote:
> > > On Sun, Jun 8, 2025 at 9:32 PM Byungchul Park <byungchul@...com> wrote:
> > > > 
> > > > To simplify struct page, the effort to separate its own descriptor from
> > > > struct page is required and the work for page pool is on going.
> > > > 
> > > > To achieve that, all the code should avoid directly accessing page pool
> > > > members of struct page.
> > > > 
> > > > Access ->pp_magic through struct netmem_desc instead of directly
> > > > accessing it through struct page in page_pool_page_is_pp().  Plus, move
> > > > page_pool_page_is_pp() from mm.h to netmem.h to use struct netmem_desc
> > > > without header dependency issue.
> > > > 
> > > > Signed-off-by: Byungchul Park <byungchul@...com>
> > > > Reviewed-by: Toke Høiland-Jørgensen <toke@...hat.com>
> > > > ---
> > > >   include/linux/mm.h   | 12 ------------
> > > >   include/net/netmem.h | 14 ++++++++++++++
> > > >   mm/page_alloc.c      |  1 +
> > > >   3 files changed, 15 insertions(+), 12 deletions(-)
> > > > 
> > > > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > > > index e51dba8398f7..f23560853447 100644
> > > > --- a/include/linux/mm.h
> > > > +++ b/include/linux/mm.h
> > > > @@ -4311,16 +4311,4 @@ int arch_lock_shadow_stack_status(struct task_struct *t, unsigned long status);
> > > >    */
> > > >   #define PP_MAGIC_MASK ~(PP_DMA_INDEX_MASK | 0x3UL)
> > > > 
> > > > -#ifdef CONFIG_PAGE_POOL
> > > > -static inline bool page_pool_page_is_pp(struct page *page)
> > > > -{
> > > > -       return (page->pp_magic & PP_MAGIC_MASK) == PP_SIGNATURE;
> > > > -}
> > > > -#else
> > > > -static inline bool page_pool_page_is_pp(struct page *page)
> > > > -{
> > > > -       return false;
> > > > -}
> > > > -#endif
> > > > -
> > > >   #endif /* _LINUX_MM_H */
> > > > diff --git a/include/net/netmem.h b/include/net/netmem.h
> > > > index d84ab624b489..8f354ae7d5c3 100644
> > > > --- a/include/net/netmem.h
> > > > +++ b/include/net/netmem.h
> > > > @@ -56,6 +56,20 @@ NETMEM_DESC_ASSERT_OFFSET(pp_ref_count, pp_ref_count);
> > > >    */
> > > >   static_assert(sizeof(struct netmem_desc) <= offsetof(struct page, _refcount));
> > > > 
> > > > +#ifdef CONFIG_PAGE_POOL
> > > > +static inline bool page_pool_page_is_pp(struct page *page)
> > > > +{
> > > > +       struct netmem_desc *desc = (struct netmem_desc *)page;
> > > > +
> > > > +       return (desc->pp_magic & PP_MAGIC_MASK) == PP_SIGNATURE;
> > > > +}
> > > > +#else
> > > > +static inline bool page_pool_page_is_pp(struct page *page)
> > > > +{
> > > > +       return false;
> > > > +}
> > > > +#endif
> > > > +
> > > >   /* net_iov */
> > > > 
> > > >   DECLARE_STATIC_KEY_FALSE(page_pool_mem_providers);
> > > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > > > index 4f29e393f6af..be0752c0ac92 100644
> > > > --- a/mm/page_alloc.c
> > > > +++ b/mm/page_alloc.c
> > > > @@ -55,6 +55,7 @@
> > > >   #include <linux/delayacct.h>
> > > >   #include <linux/cacheinfo.h>
> > > >   #include <linux/pgalloc_tag.h>
> > > > +#include <net/netmem.h>
> > > 
> > > mm files starting to include netmem.h is a bit interesting. I did not
> > > expect/want dependencies outside of net. If anything the netmem stuff
> > > include linux/mm.h
> > 
> > That's what I also concerned.  However, now that there are no way to
> > check the type of memory in a general way but require to use one of pp
> > fields, page_pool_page_is_pp() should be served by pp code e.i. network
> > subsystem.
> > 
> > This should be changed once either 1) mm provides a general way to check
> > the type or 2) pp code is moved to mm code.  I think this approach
> > should acceptable until then.
> 
> I'd argue in the end the helper should be in mm.h as mm is going to
> dictate how to check the type and keep them enumerated.

Definitely yes, I agree.  However, mm cannot do that for now.  With the
current way, it should be served by pp code since the type checking is
done through the pp fields.

	Byungchul
> 
> Reviewed-by: Pavel Begunkov <asml.silence@...il.com>
> 
> -- 
> Pavel Begunkov