linux-kernel - Re: [PATCH v2 4/8] vdso: Introduce vdso/page.h

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Message-ID: <645e5f3f-debf-4f68-ad75-4fb749b07a5b@arm.com>
Date: Tue, 24 Sep 2024 15:10:58 +0100
From: Vincenzo Frascino <vincenzo.frascino@....com>
To: Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
 Linux-Arch <linux-arch@...r.kernel.org>, linux-mm@...ck.org
Cc: Andy Lutomirski <luto@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
 "Jason A . Donenfeld" <Jason@...c4.com>,
 Christophe Leroy <christophe.leroy@...roup.eu>,
 Michael Ellerman <mpe@...erman.id.au>, Nicholas Piggin <npiggin@...il.com>,
 Naveen N Rao <naveen@...nel.org>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 "H. Peter Anvin" <hpa@...or.com>, Theodore Ts'o <tytso@....edu>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Steven Rostedt <rostedt@...dmis.org>, Masami Hiramatsu
 <mhiramat@...nel.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: Re: [PATCH v2 4/8] vdso: Introduce vdso/page.h



On 23/09/2024 17:54, Arnd Bergmann wrote:
> On Mon, Sep 23, 2024, at 14:19, Vincenzo Frascino wrote:
>> The VDSO implementation includes headers from outside of the
>> vdso/ namespace.
>>
>> Introduce vdso/page.h to make sure that the generic library
>> uses only the allowed namespace.
>>
>> Cc: Andy Lutomirski <luto@...nel.org>
>> Cc: Thomas Gleixner <tglx@...utronix.de>
>> Cc: Jason A. Donenfeld <Jason@...c4.com>
>> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@....com>
> 
> Thanks for the new version. This looks all good, just some
> very minor ideas for how to possibly improve the new version:
> 

Thanks Arnd.

>> +/* PAGE_SHIFT determines the page size */
>> +#define PAGE_SHIFT      CONFIG_PAGE_SHIFT
>> +
>> +#define PAGE_SIZE	(_AC(1,UL) << PAGE_SHIFT)
>> +
>> +#if defined(CONFIG_PHYS_ADDR_T_64BIT) && !defined(CONFIG_X86_64)
>> +#define PAGE_MASK	(~((1 << PAGE_SHIFT) - 1))
>> +#else
>> +#define PAGE_MASK	(~(PAGE_SIZE-1))
>> +#endif
> 
> I would open-code the CONFIG_PAGE_SHIFT in PAGE_SIZE
> and PAGE_MASK, just to avoid the extra indirection in the
> preprocessor. This mainly has the benefit of slightly
> shorter compiler warnings when all the macros get
> traced back but can also slightly improve compile speed
> in case this is used in deeply nested macros.
> 

I will fix it in the next iteration.

> Without a comment, the special case for CONFIG_X86_64
> not very clear, and probably not needed. If you are
> worried about introducing an architecture specific
> regression, I would suggest instead explaining the
> possible issue in the patch description but using the
> more generic and simpler #ifdef check.
> 

If I do not add the #ifdef, it does not build. But you are right, I should have
put a comment in the commit message.

Regression below:

drivers/gpu/drm/i915/gt/intel_gt_print.h:29:36: error: format ‘%lx’ expects
argument of type ‘long unsigned int’, but argument 6 has type ‘u32’ {aka
‘unsigned int’} [-Werror=format=]
   29 |         drm_dbg(&(_gt)->i915->drm, "GT%u: " _fmt, (_gt)->info.id,
##__VA_ARGS__)
      |                                    ^~~~~~~~
include/drm/drm_print.h:424:39: note: in definition of macro ‘drm_dev_dbg’
  424 |         __drm_dev_dbg(NULL, dev, cat, fmt, ##__VA_ARGS__)
      |                                       ^~~
include/drm/drm_print.h:524:33: note: in expansion of macro ‘drm_dbg_driver’
  524 | #define drm_dbg(drm, fmt, ...)  drm_dbg_driver(drm, fmt, ##__VA_ARGS__)
      |                                 ^~~~~~~~~~~~~~
linux/drivers/gpu/drm/i915/gt/intel_gt_print.h:29:9: note: in expansion of macro
‘drm_dbg’
   29 |         drm_dbg(&(_gt)->i915->drm, "GT%u: " _fmt, (_gt)->info.id,
##__VA_ARGS__)
      |         ^~~~~~~
drivers/gpu/drm/i915/gt/intel_gt.c:310:25: note: in expansion of macro ‘gt_dbg’
  310 |                         gt_dbg(gt, "Unexpected fault\n"
      |                         ^~~~~~

I am open to alternative suggestions.

>       Arnd

-- 
Regards,
Vincenzo