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

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Date: Fri, 1 Mar 2024 17:09:21 +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 2/9] x86/startup_64: Defer assignment of 5-level
 paging global variables

On Fri, Mar 01, 2024 at 11:01:33AM +0100, Ard Biesheuvel wrote:
> The scenario that I have not managed to test is entering from EFI with
> 5 levels of paging enabled, and switching back to 4 levels (which
> should work regardless of CONFIG_X86_5LEVEL). However, no firmware in
> existence actually supports that today, and I am pretty sure that this
> code has never been tested under those conditions to begin with. (OVMF
> patches are under review atm to allow 5-level paging to be enabled in
> the firmware)

Aha.

> I currently don't have access to real hardware with LA57 support so
> any additional coverage there is highly appreciated (same for the last
> patch in this series)

Right, I'm sure dhansen could dig up such a machine. We'll ask him
nicely to test when the set is ready.

Thx.

-- 
Regards/Gruss,
    Boris.

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