netdev - Re: [PATCH 01/18] netmem: introduce struct netmem_desc struct_group_tagged()'ed on struct net

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: <87bjrjn1ki.fsf@toke.dk>
Date: Fri, 23 May 2025 11:01:01 +0200
From: Toke Høiland-Jørgensen <toke@...hat.com>
To: Byungchul Park <byungchul@...com>, willy@...radead.org,
 netdev@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 kernel_team@...ynix.com, kuba@...nel.org, almasrymina@...gle.com,
 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, asml.silence@...il.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 01/18] netmem: introduce struct netmem_desc
 struct_group_tagged()'ed on struct net_iov

Byungchul Park <byungchul@...com> writes:

> To simplify struct page, the page pool members of struct page should be
> moved to other, allowing these members to be removed from struct page.
>
> Introduce a network memory descriptor to store the members, struct
> netmem_desc, reusing struct net_iov that already mirrored struct page.
>
> While at it, relocate _pp_mapping_pad to group struct net_iov's fields.
>
> Signed-off-by: Byungchul Park <byungchul@...com>
> ---
>  include/linux/mm_types.h |  2 +-
>  include/net/netmem.h     | 43 +++++++++++++++++++++++++++++++++-------
>  2 files changed, 37 insertions(+), 8 deletions(-)
>
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 56d07edd01f9..873e820e1521 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -120,13 +120,13 @@ struct page {
>  			unsigned long private;
>  		};
>  		struct {	/* page_pool used by netstack */
> +			unsigned long _pp_mapping_pad;
>  			/**
>  			 * @pp_magic: magic value to avoid recycling non
>  			 * page_pool allocated pages.
>  			 */
>  			unsigned long pp_magic;
>  			struct page_pool *pp;
> -			unsigned long _pp_mapping_pad;
>  			unsigned long dma_addr;
>  			atomic_long_t pp_ref_count;
>  		};

The reason that field is called "_pp_mapping_pad" is that it's supposed
to overlay the page->mapping field, so that none of the page_pool uses
set a value here. Moving it breaks that assumption. Once struct
netmem_desc is completely decoupled from struct page this obviously
doesn't matter, but I think it does today? At least, trying to use that
field for the DMA index broke things, which is why we ended up with the
bit-stuffing in pp_magic...

-Toke