linux-kernel - Re: [PATCH v7 3/9] x86/startup_64: Simplify calculation of initial page table address

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Message-ID: <20240228212751.GJZd-lVzA6B9yIe0Zk@fat_crate.local>
Date: Wed, 28 Feb 2024 22:27:51 +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 3/9] x86/startup_64: Simplify calculation of initial
 page table address

On Tue, Feb 27, 2024 at 04:19:11PM +0100, Ard Biesheuvel wrote:
> From: Ard Biesheuvel <ardb@...nel.org>
> 
> Determining the address of the initial page table to program into CR3
> involves:
> - taking the physical address
> - adding the SME encryption mask
> 
> On the primary entry path, the code is mapped using a 1:1 virtual to
> physical translation, so the physical address can be taken directly
> using a RIP-relative LEA instruction.
> 
> On the secondary entry path, the address can be obtained by taking the
> offset from the virtual kernel base (__START_kernel_map) and adding the
> physical kernel base.
> 
> This is implemented in a slightly confusing way, so clean this up.
> 
> Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
> ---
>  arch/x86/kernel/head_64.S | 25 ++++++--------------
>  1 file changed, 7 insertions(+), 18 deletions(-)

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

-- 
Regards/Gruss,
    Boris.

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