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

["David Hildenbrand (Red Hat)" <david@kernel.org>]

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