linux-kernel - Re: [PATCH v2] x86/pm: fix false positive kmemleak report in msr_build

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Date:   Tue, 26 Apr 2022 19:27:59 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Matthieu Baerts <matthieu.baerts@...sares.net>,
        Pavel Machek <pavel@....cz>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>, Chen Yu <yu.c.chen@...el.com>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Linux Memory Management List <linux-mm@...ck.org>,
        Mat Martineau <mathew.j.martineau@...ux.intel.com>,
        Ingo Molnar <mingo@...nel.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] x86/pm: fix false positive kmemleak report in
 msr_build_context()

On Tue, Apr 26, 2022 at 06:24:04PM +0200, Rafael J. Wysocki wrote:
> So can the comment be dropped entirely?

Looks like it to me. All the accesses in wakeup_64.S are done through
those offsets which are computed at build-time so they should always be
valid.

OTOH, I wouldn't mind having there some text making any future person
touching this, aware of where to look when making changes.

Some changes like removing a struct member are nicely caught, ofc,
see below. But for something else which is a lot more subtle having a
comment say "hey, have a look at where this is used in wakeup_64.S and
make sure everything is still kosher" is better than having no comment
at all. IMHO.

Thx.

In file included from arch/x86/kernel/asm-offsets.c:14:
arch/x86/kernel/asm-offsets_64.c: In function ‘main’:
./include/linux/stddef.h:16:33: error: ‘struct saved_context’ has no member named ‘gdt_desc’
   16 | #define offsetof(TYPE, MEMBER)  __builtin_offsetof(TYPE, MEMBER)
      |                                 ^~~~~~~~~~~~~~~~~~
./include/linux/kbuild.h:6:69: note: in definition of macro ‘DEFINE’
    6 |         asm volatile("\n.ascii \"->" #sym " %0 " #val "\"" : : "i" (val))
      |                                                                     ^~~
./include/linux/kbuild.h:11:21: note: in expansion of macro ‘offsetof’
   11 |         DEFINE(sym, offsetof(struct str, mem))
      |

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette