linux-kernel - Re: [PATCH v3 1/7] x86/cpu: Use a new feature flag for 5 level paging

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: <20250515103906.GEaCXESqcyPcQn6xlc@fat_crate.local>
Date: Thu, 15 May 2025 12:39:06 +0200
From: Borislav Petkov <bp@...en8.de>
To: Ard Biesheuvel <ardb@...nel.org>
Cc: Ard Biesheuvel <ardb+git@...gle.com>, linux-kernel@...r.kernel.org,
	x86@...nel.org, Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Brian Gerst <brgerst@...il.com>
Subject: Re: [PATCH v3 1/7] x86/cpu: Use a new feature flag for 5 level paging

On Thu, May 15, 2025 at 11:17:47AM +0100, Ard Biesheuvel wrote:
> I'd lean towards not lying about whether the CPU is la57 capable in
> /proc/cpuinfo if we don't have to - this flag directly reflects the
> CPUID leaf.

We have a whole documentation about that whole "not lying" thing: short
version - use kcpuid or some other cpuid tool:

Documentation/arch/x86/cpuinfo.rst

> This is arguably the important one: as long as "la57" does not change
> meaning, we should be fine from compatibility pov.

Yes, those flags in /proc/cpuinfo should show that something is enabled and in
use. And it makes sense here. And you can't change that string anyway anymore.

Whether the hw is capable is not important for userspace and there are a lot
better means for it.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette