linux-kernel - Re: [PATCH v2 0/2] x86: Fix kexec 5-level to 4-level paging transition

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Message-ID: <20251029204814.GHaQJ9jhw4u5SU1rNJ@fat_crate.local>
Date: Wed, 29 Oct 2025 21:48:14 +0100
From: Borislav Petkov <bp@...en8.de>
To: Usama Arif <usamaarif642@...il.com>
Cc: dwmw@...zon.co.uk, tglx@...utronix.de, mingo@...hat.com,
	dave.hansen@...ux.intel.com, ardb@...nel.org, hpa@...or.com,
	x86@...nel.org, apopple@...dia.com, thuth@...hat.com,
	nik.borisov@...e.com, kas@...nel.org, linux-kernel@...r.kernel.org,
	linux-efi@...r.kernel.org, kernel-team@...a.com,
	Michael van der Westhuizen <rmikey@...a.com>,
	Tobias Fleig <tfleig@...a.com>
Subject: Re: [PATCH v2 0/2] x86: Fix kexec 5-level to 4-level paging
 transition

On Tue, Oct 28, 2025 at 10:55:55AM +0000, Usama Arif wrote:
> This series addresses critical bugs in the kexec path when transitioning
> from a kernel using 5-level page tables to one using 4-level page tables.

Out of curiosity: what is the real-life use case for this?

Judging by the Reported-by's I guess Meta is doing some kexec-ing into default
kernels which are 4-level so that they can work on any machine ...

Close?

-- 
Regards/Gruss,
    Boris.

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