linux-kernel - Re: [PATCH RFC] kexec: add option to print previous kernel release after kexec

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Message-ID: <CA+CK2bDCKQrK3+6832Lxw8fZx_yt+8z0fFPdugC59p1zdSeSZQ@mail.gmail.com>
Date: Tue, 30 Dec 2025 10:03:38 -0500
From: Pasha Tatashin <pasha.tatashin@...een.com>
To: Breno Leitao <leitao@...ian.org>
Cc: Alexander Graf <graf@...zon.com>, Mike Rapoport <rppt@...nel.org>, 
	Pratyush Yadav <pratyush@...nel.org>, linux-kernel@...r.kernel.org, 
	kexec@...ts.infradead.org, linux-mm@...ck.org, usamaarif642@...il.com, 
	rmikey@...a.com, clm@...com, riel@...riel.com, kernel-team@...a.com
Subject: Re: [PATCH RFC] kexec: add option to print previous kernel release
 after kexec

On Tue, Dec 30, 2025 at 9:13 AM Breno Leitao <leitao@...ian.org> wrote:
>
> Introduce a new Kconfig option, CONFIG_KEXEC_SHOW_PREVIOUS_RELEASE,

I don't think we need a config for this. Let's just show the previous
kernel version unconditionally when KHO is enabled.

> which enables the storage and display of the previous kernel's release
> version across kexec boots when using Kexec Handover (KHO).
>
> Motivation
> ==========
>
> Kernel bugs that depend on the version of the previously running kernel
> are not uncommon, especially in scenarios where a buggy kernel kexecs
> into a new one and the issue only manifests in the subsequent kernel.
>
> Recent examples include:
>
>  * eb2266312507 ("x86/boot: Fix page table access in 5-level to 4-level paging transition")
>  * 77d48d39e991 ("efistub/tpm: Use ACPI reclaim memory for event log to avoid corruption")
>  * 64b45dd46e15 ("x86/efi: skip memattr table on kexec boot")
>
> As kexec-based reboots become more widespread among Linux users, these
> issues are becoming increasingly prominent.
>
> When such crashes occur, correlating them to the previous kernel version
> is challenging, especially at scale, where the problem may only appear in
> specific cases and it is hard to correlate.
>
> With the introduction of Kexec Handover (KHO), we now have a reliable
> mechanism to pass information between kernels. This presents an
> opportunity to address the problem by carrying the previous kernel's
> release version to the next kernel and printing it at boot time.

LUO added the number of times a machine has been live updated to help
debugging problems that are related to live update, perhaps, in
addition to the previous kernel version, we should also add a number
of times the machine has been kexec'd. It is useful when a bug
manifests only after a number of kexec's which is also sometimes a
case.

Pasha