linux-kernel - Re: [PATCHv3 0/4] x86: Make 5-level paging support unconditional for x86-64

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Message-ID: <aCc5cm_ZC-y9OnyA@gmail.com>
Date: Fri, 16 May 2025 15:11:14 +0200
From: Ingo Molnar <mingo@...nel.org>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc: 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>,
	Juergen Gross <jgross@...e.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,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCHv3 0/4] x86: Make 5-level paging support unconditional for
 x86-64


* Kirill A. Shutemov <kirill.shutemov@...ux.intel.com> 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.
> 
> In preparation to that remove CONFIG_DYNAMIC_MEMORY_LAYOUT and make
> SPARSEMEM_VMEMMAP the only memory model.
> 
> v3:
>  - Drop few "#if CONFIG_PGTABLE_LEVELS >= 5";
>  - Make PARAVIRT_XXL 64-bit explicitly and drop ifdefs
>    to support PGTABLE_LEVELS < 5;
>  - Add Reviewed-by tags from Ard;
> v2:
>  - Fix 32-bit build by wrapping p4d_set_huge() and p4d_clear_huge() in
>    #if CONFIG_PGTABLE_LEVELS > 4;
>  - Rebased onto current tip/master;

Wow, -v1 was sent almost a year ago. :-)

> Kirill A. Shutemov (4):
>   x86/64/mm: Always use dynamic memory layout
>   x86/64/mm: Make SPARSEMEM_VMEMMAP the only memory model
>   x86/64/mm: Make 5-level paging support unconditional
>   x86/paravirt: Restrict PARAVIRT_XXL to 64-bit only

>  24 files changed, 14 insertions(+), 142 deletions(-)

Okay, this series makes a lot of sense, because in practice all major 
distros have 5-level paging enabled:

  .config.opensuse.default:     CONFIG_X86_5LEVEL=y
  .config.ubuntu.localinstall:  CONFIG_X86_5LEVEL=y
  .config.fedora.generic:       CONFIG_X86_5LEVEL=y
  .config.rhel.generic:         CONFIG_X86_5LEVEL=y

So the !CONFIG_X86_5LEVEL case gets very little runtime testing by 
distributions and users.

So I've applied the first two patches to tip:x86/core:

  x86/mm/64: Always use dynamic memory layout
  x86/mm/64: Make SPARSEMEM_VMEMMAP the only memory model

as they are fairly straightforward.

Patch #3:

  x86/64/mm: Make 5-level paging support unconditional

... might have to wait until after v6.16-rc1, as it's a higher risk 
patch.

  x86/paravirt: Restrict PARAVIRT_XXL to 64-bit only

... and this one depends on patch #3.

Does this approach sound good to everyone?

Thanks,

	Ingo