linux-kernel - Re: [RFC PATCH 2/4] mm: Add support for unaccepted memory hotplug

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Message-ID: <20251127181233.GBaSiUkaLzwANS_6WT@fat_crate.local>
Date: Thu, 27 Nov 2025 19:12:33 +0100
From: Borislav Petkov <bp@...en8.de>
To: Kiryl Shutsemau <kas@...nel.org>
Cc: "Pratik R. Sampat" <prsampat@....com>, linux-mm@...ck.org,
	linux-coco@...ts.linux.dev, linux-efi@...r.kernel.org,
	x86@...nel.org, linux-kernel@...r.kernel.org, tglx@...utronix.de,
	mingo@...hat.com, dave.hansen@...ux.intel.com, ardb@...nel.org,
	akpm@...ux-foundation.org, david@...hat.com, osalvador@...e.de,
	thomas.lendacky@....com, michael.roth@....com
Subject: Re: [RFC PATCH 2/4] mm: Add support for unaccepted memory hotplug

On Thu, Nov 27, 2025 at 05:35:57PM +0000, Kiryl Shutsemau wrote:
> > ABI break for kexec? Is that a thing?
> > 
> > Since when do we enforce ABI compatibility for kexec and where are we
> > documenting that?

I'll take that as a "no".

> The whole purpose of kexec() is to switch between kernel versions. This
> struct defines format we communicate information about unaccepted memory
> between kernels. The mismatch will lead to boot failure.
> 
> The structure is versioned. Ideally, we should know the format of the
> structure the next kernel supports and act accordingly in the first
> kernel. Like, we can accept all memory before kexec on mismatch.

None of that matters if you kexec the same kernels.

IOW, for some reason you want to be able to kexec different kernels. The
question is why do we care?

AFAICT, nowhere do we say that there's an ABI between kexec-ed kernels...

Thx.

-- 
Regards/Gruss,
    Boris.

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