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

[David Hildenbrand (Red Hat)]

On 11/28/25 12:34, Borislav Petkov wrote:
> On Fri, Nov 28, 2025 at 10:30:15AM +0100, David Hildenbrand (Red Hat) wrote:
> > 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?
>
> And my question is: since when do we enforce no-ABI-changes between kernels so
> that we can kexec any kernel into any kernel?
>
> By that logic I should be able to kexec 5.x into 6.x. I'll bet some money that
> it won't work.

I *think* ordinary kexec would likely work, as I recall that it doesn't 
need a lot of that special kexec ABI sauce like unaccepted memory uses.

Within confidential VMs (kexec ...) I am pretty sure that it's a 
different discussion.

> So unless it is written down somewhere, I think we should probably talk first
> what we want to support and why...
>
> Makes sense?

Makes sense to me, especially for confidential VMs where we pass such 
kernel-managed data from the old to the new kernel.

--
Cheers

David