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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <kdahkhurbpls5gtmwqyvmgwk6qnczyekvn4nog5hbze2ev7nk3@rqeiw4qovki2>
Date: Fri, 16 May 2025 14:51:38 +0300
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: Jürgen Groß <jgross@...e.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 Fri, May 16, 2025 at 02:47:46PM +0300, 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?

Oh. It is PARAVIRT_XXL thingy which is only used by XEN_PV which is 64-bit
only, right?

Do we want to make PARAVIRT_XXL explicitly 64-bit only?

-- 
  Kiryl Shutsemau / Kirill A. Shutemov