linux-kernel - Re: [PATCH 0/3] x86/mce: Fix more noinstr fun

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Message-ID: <Yf08yMZZDCtYMBVX@zn.tnic>
Date:   Fri, 4 Feb 2022 15:48:40 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Marco Elver <elver@...gle.com>
Cc:     Tony Luck <tony.luck@...el.com>, Jakub Kicinski <kuba@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/3] x86/mce: Fix more noinstr fun

On Fri, Feb 04, 2022 at 12:24:00PM +0100, Marco Elver wrote:
> I guess to solve noinstr "calling" something else the only solution is
> to make the other function noinstr as well, or __always_inline.
> 
> Have you considered making some of these other functions 'noinstr' as
> well? I guess __always_inline works, esp. if there's just 1 caller.
> And by the looks of it you're getting a net .text reduction, so

Yeah, I started doing that and the savings were the persuasive
argument.

Even more so if the function has one caller only and gets inlined,
normally. I guess it doesn't get inlined when there's KASAN
instrumentation or so but I haven't verified it fully why.

Because even for oneliners like v8086_mode() which should get inlined
trivially, the compiler ends up doing this constprop thing - I guess
some constants folding optimization thing... it probably doesn't even
matter so much whether oneliners get inlined in KASAN-enabled builds so
I guess we might just as well force-inline them for the other configs.

> Acked-by: Marco Elver <elver@...gle.com>

Thx.

-- 
Regards/Gruss,
    Boris.

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