linux-kernel - Re: [PATCHv2 3/3] x86/64/mm: Make 5-level paging support unconditional

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Message-ID: <fca54172-f6f5-4594-8d87-58f5dad56244@suse.com>
Date: Fri, 16 May 2025 13:51:03 +0200
From: Juergen Gross <jgross@...e.com>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc: "Kirill A. Shutemov" <kirill@...temov.name>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
 Jonathan Corbet <corbet@....net>, Andy Lutomirski <luto@...nel.org>,
 Peter Zijlstra <peterz@...radead.org>, Ard Biesheuvel <ardb@...nel.org>,
 Jan Kiszka <jan.kiszka@...mens.com>, Kieran Bingham <kbingham@...nel.org>,
 Michael Roth <michael.roth@....com>,
 Rick Edgecombe <rick.p.edgecombe@...el.com>,
 Brijesh Singh <brijesh.singh@....com>, Sandipan Das <sandipan.das@....com>,
 Tom Lendacky <thomas.lendacky@....com>, linux-kernel@...r.kernel.org,
 linux-doc@...r.kernel.org, linux-efi@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCHv2 3/3] x86/64/mm: Make 5-level paging support
 unconditional

On 16.05.25 13:47, Kirill A. Shutemov wrote:
> On Fri, May 16, 2025 at 01:29:27PM +0200, Jürgen Groß wrote:
>> On 16.05.25 13:09, Kirill A. Shutemov wrote:
>>> On Fri, May 16, 2025 at 12:42:21PM +0200, Jürgen Groß wrote:
>>>> On 16.05.25 11:15, Kirill A. Shutemov wrote:
>>>>> Both Intel and AMD CPUs support 5-level paging, which is expected to
>>>>> become more widely adopted in the future.
>>>>>
>>>>> Remove CONFIG_X86_5LEVEL and ifdeffery for it to make it more readable.
>>>>>
>>>>> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
>>>>> Suggested-by: Borislav Petkov <bp@...en8.de>
>>>>> ---
>>>>>     Documentation/arch/x86/cpuinfo.rst            |  8 +++----
>>>>>     .../arch/x86/x86_64/5level-paging.rst         |  9 --------
>>>>>     arch/x86/Kconfig                              | 22 +------------------
>>>>>     arch/x86/Kconfig.cpufeatures                  |  4 ----
>>>>>     arch/x86/boot/compressed/pgtable_64.c         | 11 ++--------
>>>>>     arch/x86/boot/header.S                        |  4 ----
>>>>>     arch/x86/boot/startup/map_kernel.c            |  5 +----
>>>>>     arch/x86/include/asm/page_64.h                |  2 --
>>>>>     arch/x86/include/asm/page_64_types.h          |  7 ------
>>>>>     arch/x86/include/asm/pgtable_64_types.h       | 18 ---------------
>>>>>     arch/x86/kernel/alternative.c                 |  2 +-
>>>>>     arch/x86/kernel/head64.c                      |  2 --
>>>>>     arch/x86/kernel/head_64.S                     |  2 --
>>>>>     arch/x86/mm/init.c                            |  4 ----
>>>>>     arch/x86/mm/pgtable.c                         |  2 +-
>>>>>     drivers/firmware/efi/libstub/x86-5lvl.c       |  2 +-
>>>>>     16 files changed, 10 insertions(+), 94 deletions(-)
>>>>
>>>> There are some instances of:
>>>>
>>>> #if CONFIG_PGTABLE_LEVELS >= 5
>>>>
>>>> in 64-bit-only code under arch/x86, which could be simplified, too.
>>>>
>>>> They are still correct, but I wanted to hint at further code removals
>>>> being possible.
>>>
>>> Okay, fair enough. Fixup is below.
>>>
>>> Did I miss anything else?
>>
>> Yes.
>>
>> One more instance in arch/x86/xen/mmu_pv.c,
> 
> Ah. Right.
> 
>> one in arch/x86/include/asm/paravirt.h,
>> one in arch/x86/include/asm/paravirt_types.h,
>> one in arch/x86/kernel/paravirt.c
> 
> Hm. Is paravirt 64-bit only?
> 

CONFIG_PARAVIRT_XXL is.


Juergen

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