linux-kernel - Re: [PATCH v7 2/9] x86/startup_64: Defer assignment of 5-level paging global variables

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Date: Wed, 28 Feb 2024 21:55:40 +0100
From: Borislav Petkov <bp@...en8.de>
To: Ard Biesheuvel <ardb+git@...gle.com>
Cc: linux-kernel@...r.kernel.org, Ard Biesheuvel <ardb@...nel.org>,
	Kevin Loughlin <kevinloughlin@...gle.com>,
	Tom Lendacky <thomas.lendacky@....com>,
	Dionna Glaze <dionnaglaze@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Andy Lutomirski <luto@...nel.org>, Brian Gerst <brgerst@...il.com>
Subject: Re: [PATCH v7 2/9] x86/startup_64: Defer assignment of 5-level
 paging global variables

On Tue, Feb 27, 2024 at 04:19:10PM +0100, Ard Biesheuvel wrote:
> From: Ard Biesheuvel <ardb@...nel.org>
> 
> Assigning the 5-level paging related global variables from the earliest
> C code using explicit references that use the 1:1 translation of memory
> is unnecessary, as the startup code itself does not rely on them to
> create the initial page tables, and this is all it should be doing. So
> defer these assignments to the primary C entry code that executes via
> the ordinary kernel virtual mapping.
> 
> Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
> ---
>  arch/x86/include/asm/pgtable_64_types.h |  2 +-
>  arch/x86/kernel/head64.c                | 44 +++++++-------------
>  2 files changed, 15 insertions(+), 31 deletions(-)

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

Those should probably be tested on a 5level machine, just in case.

Thx.

-- 
Regards/Gruss,
    Boris.

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