linux-kernel - Re: [PATCHv7 15/19] x86/mm: Replace compile-time checks for 5-level with runtime-time

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Date:   Thu, 28 Sep 2017 10:35:24 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...capital.net>,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        Borislav Petkov <bp@...e.de>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCHv7 15/19] x86/mm: Replace compile-time checks for 5-level
 with runtime-time


* Kirill A. Shutemov <kirill.shutemov@...ux.intel.com> wrote:

> This patch converts the of CONFIG_X86_5LEVEL check to runtime checks for
> p4d folding.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> ---
>  arch/x86/mm/fault.c            |  2 +-
>  arch/x86/mm/ident_map.c        |  2 +-
>  arch/x86/mm/init_64.c          | 30 ++++++++++++++++++------------
>  arch/x86/mm/kasan_init_64.c    | 12 ++++++------
>  arch/x86/mm/kaslr.c            |  6 +++---
>  arch/x86/platform/efi/efi_64.c |  2 +-
>  arch/x86/power/hibernate_64.c  |  6 +++---
>  7 files changed, 33 insertions(+), 27 deletions(-)

> +/*
> + * When memory was added make sure all the processes MM have
> + * suitable PGD entries in the local PGD level page.
> + */
> +void sync_global_pgds(unsigned long start, unsigned long end)
> +{
> +	if (pgtable_l5_enabled)
> +		sync_global_pgds_57(start, end);
> +	else
> +		sync_global_pgds_48(start, end);
> +}

We should use the _l4 and _l5 postfixes instead of random _57 and _48 that is 
pretty cryptic to most readers of the code.

Thanks,

	Ingo