linux-kernel - Re: [PATCH 21/26] x86/mm: add support of additional page table level during early boot

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Message-ID: <20170313071810.GA28726@gmail.com>
Date:   Mon, 13 Mar 2017 08:18:10 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Arnd Bergmann <arnd@...db.de>,
        "H. Peter Anvin" <hpa@...or.com>, Andi Kleen <ak@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Andy Lutomirski <luto@...capital.net>,
        Michal Hocko <mhocko@...e.com>, linux-arch@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 21/26] x86/mm: add support of additional page table level
 during early boot


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

> This patch adds support for 5-level paging during early boot.
> It generalizes boot for 4- and 5-level paging on 64-bit systems with
> compile-time switch between them.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> ---
>  arch/x86/boot/compressed/head_64.S          | 23 +++++++++--
>  arch/x86/include/asm/pgtable.h              |  2 +-
>  arch/x86/include/asm/pgtable_64.h           |  6 ++-
>  arch/x86/include/uapi/asm/processor-flags.h |  2 +
>  arch/x86/kernel/espfix_64.c                 |  2 +-
>  arch/x86/kernel/head64.c                    | 40 +++++++++++++-----
>  arch/x86/kernel/head_64.S                   | 63 +++++++++++++++++++++--------

Ok, here I'd like to have a C version instead of further complicating an already 
complex assembly version...

I.e. the existing setup code should be converted to C in one patch, and then 
another patch should add 5-level paging support to the C code.

See how this was done for the 32-bit setup code already:

  5a7670ee23f2 x86/boot/32: Convert the 32-bit pgtable setup code from assembly to C

Also, please split it up into per boot path and topic, i.e. have a sparate patch 
for the Xen bits, the KASAN bits, the kexec extension, etc.

Thanks,

	Ingo