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

[David Hildenbrand (Red Hat)]

On 11/27/25 19:12, Borislav Petkov wrote:
> 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?

kexecing the same kernel is typically used for kdump purposes.

kexecing different kernels is used for all sorts of things 
(live-upgrade, grub-emu come to mind). It's quite common to kexec 
different kernels, or maybe I misunderstood the question here?

--
Cheers

David