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

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Message-ID: <20250516153009.GEaCdaAdhCVpjaViSx@fat_crate.local>
Date: Fri, 16 May 2025 17:30:09 +0200
From: Borislav Petkov <bp@...en8.de>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
	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
Subject: Re: [PATCHv2 3/3] x86/64/mm: Make 5-level paging support
 unconditional

On Fri, May 16, 2025 at 12:15:33PM +0300, Kirill A. Shutemov wrote:
> @@ -173,10 +173,10 @@ For example, when an old kernel is running on new hardware.
>  The kernel disabled support for it at compile-time
>  --------------------------------------------------
>  
> -For example, if 5-level-paging is not enabled when building (i.e.,
> -CONFIG_X86_5LEVEL is not selected) the flag "la57" will not show up [#f1]_.
> +For example, if Linear Address Masking (LAM) is not enabled when building (i.e.,
> +CONFIG_ADDRESS_MASKING is not selected) the flag "lam" will not show up.
>  Even though the feature will still be detected via CPUID, the kernel disables
> -it by clearing via setup_clear_cpu_cap(X86_FEATURE_LA57).
> +it by clearing via setup_clear_cpu_cap(X86_FEATURE_LAM).

LOL, good one.

The rest looks nice and good to me. And FWIW, it boots fine on my Zen5 with
5lvl enabled.

Reviewed-by: Borislav Petkov (AMD) <bp@...en8.de>

Thx.

-- 
Regards/Gruss,
    Boris.

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