linux-kernel - Re: [PATCH v2 0/3] bits: Split asm and non-asm GENMASK*() and unify definitions

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: <0e5988e2-eb98-4931-86b8-dcbb8b4cb605@wanadoo.fr>
Date: Mon, 30 Jun 2025 23:07:43 +0900
From: Vincent Mailhol <mailhol.vincent@...adoo.fr>
To: Yury Norov <yury.norov@...il.com>
Cc: linux-kernel@...r.kernel.org, intel-gfx@...ts.freedesktop.org,
 dri-devel@...ts.freedesktop.org, Andi Shyti <andi.shyti@...ux.intel.com>,
 David Laight <David.Laight@...LAB.COM>,
 Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
 Catalin Marinas <catalin.marinas@....com>,
 Anshuman Khandual <anshuman.khandual@....com>,
 linux-arm-kernel@...ts.infradead.org,
 Lucas De Marchi <lucas.demarchi@...el.com>,
 Rasmus Villemoes <linux@...musvillemoes.dk>,
 Jani Nikula <jani.nikula@...ux.intel.com>,
 Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
 Rodrigo Vivi <rodrigo.vivi@...el.com>, Tvrtko Ursulin
 <tursulin@...ulin.net>, David Airlie <airlied@...il.com>,
 Simona Vetter <simona@...ll.ch>, Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2 0/3] bits: Split asm and non-asm GENMASK*() and unify
 definitions

Hi Yury,

On 09/06/2025 at 11:45, Vincent Mailhol wrote:
> This is a subset of below series:
> 
>   bits: Fixed-type GENMASK_U*() and BIT_U*()
>   Link: https://lore.kernel.org/r/20250308-fixed-type-genmasks-v6-0-f59315e73c29@wanadoo.fr
> 
> Yury suggested to split the above series in two steps:
> 
>   #1 Introduce the new fixed type GENMASK_U*() (already merged upstream)
>   #2 Consolidate the existing GENMASK*()
> 
> This new series is the resulting step #2 following the split.
> 
> And thus, this series consolidate all the non-asm GENMASK*() so that
> they now all depend on GENMASK_TYPE() which was introduced in step #1.
> 
> To do so, I had to split the definition of the asm and non-asm
> GENMASK(). I think this is controversial. So I initially implemented a
> first draft in which both the asm and non-asm version would rely on
> the same helper macro, i.e. adding this:
> 
>   #define __GENMASK_TYPE(t, w, h, l)		\
>   	(((t)~_ULL(0) << (l)) &			\
>   	 ((t)~_ULL(0) >> (w - 1 - (h))))
> 
> to uapi/bits.h. And then, the different GENMASK()s would look like
> this:
> 
>   #define __GENMASK(h, l) __GENMASK_TYPE(unsigned long, __BITS_PER_LONG, h, l)
> 
> and so on.
> 
> I implemented it, and the final result looked quite ugly. Not only do
> we need to manually provide the width each time, the biggest concern
> is that adding this to the uapi is asking for trouble. Who knows how
> people are going to use this? And once it is in the uapi, there is
> virtually no way back.
> 
> Adding to this, that macro can not even be generalised to u128
> integers, whereas after the split, it can.
> 
> And so, after implementing both, the asm seems way cleaner than the
> non-asm split and is, I think, the best compromise.
> 
> Aside from the split, the asm's GENMASK() and GENMASK_ULL() are left
> untouched. While there are some strong incentives to also simplify
> these as pointed by David Laight in this thread:
> 
>   https://lore.kernel.org/all/20250309102312.4ff08576@pumpkin/
> 
> this series deliberately limit its scope to the non-asm variants.
> 
> Here are the bloat-o-meter stats:
> 
>   $ ./scripts/bloat-o-meter vmlinux_before.o vmlinux_after.o
>   add/remove: 0/0 grow/shrink: 4/2 up/down: 5/-9 (-4)
>   Function                                     old     new   delta
>   intel_psr_invalidate                         352     354      +2
>   mst_stream_compute_config                   1589    1590      +1
>   intel_psr_flush                              707     708      +1
>   intel_dp_compute_link_config                1338    1339      +1
>   intel_drrs_activate                          398     395      -3
>   cfg80211_inform_bss_data                    5137    5131      -6
>   Total: Before=23333846, After=23333842, chg -0.00%
> 
> (done with GCC 12.4.1 on an x86_64 defconfig)
> 
> --
> 2.43.0
> 
> Signed-off-by: Vincent Mailhol <mailhol.vincent@...adoo.fr>

I didn't hear back from you on this series. Are you still interested in this
cleanup or should I just abandon it?

Note that now that the GENMASK_U*() are upstream, I am done. I think that it
will be better with this clean-up, but I do not mind if we keep it as it.

Just let me know what you think.


Yours sincerely,
Vincent Mailhol