linux-kernel - Re: [PATCH v7 4/9] x86/startup_64: Simplify virtual switch on primary boot

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Message-ID: <20240301161234.GCZeH-co78aShifhAN@fat_crate.local>
Date: Fri, 1 Mar 2024 17:12:34 +0100
From: Borislav Petkov <bp@...en8.de>
To: Ard Biesheuvel <ardb@...nel.org>
Cc: Ard Biesheuvel <ardb+git@...gle.com>, linux-kernel@...r.kernel.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 4/9] x86/startup_64: Simplify virtual switch on
 primary boot

On Thu, Feb 29, 2024 at 11:36:01PM +0100, Ard Biesheuvel wrote:
> Because we enter with a 1:1 mapping, and so we can only switch to
> another set of page tables that also includes this 1:1 mapping. Once
> we are running from the kernel mapping, we can drop the 1:1 mapping
> but we still need it.
> 
> What we could do for robustness is reduce this 1:1 mapping to text +
> rodata, and make it read-only, but I'm not sure it's worth the churn.

Yeah, I was experimenting a bit with some shenanigans with those two
pagetables yesterday and arrived to a similar conclusion - there's no
point in trying to unify them.

Thx.

-- 
Regards/Gruss,
    Boris.

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