Messages in this thread |  | | Date | Wed, 3 Dec 2025 14:46:23 +0000 | | From | Kiryl Shutsemau <> | | Subject | Re: [RFC PATCH 2/4] mm: Add support for unaccepted memory hotplug |
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On Mon, Dec 01, 2025 at 09:36:58PM +0100, David Hildenbrand (Red Hat) wrote: > On 12/1/25 21:25, Borislav Petkov wrote: > > On Mon, Dec 01, 2025 at 09:10:26PM +0100, David Hildenbrand (Red Hat) wrote: > > > Just to be clear, I don't think it exist and also I don't think that it > > > should exist. > > > > By that logic if it doesn't exist and someone sends a patch, I should simply > > ignore a review comment about that patch breaking some non-existent ABI and > > simply take it. > > Well, we can always discuss and see if there is a way to not break a > specific use case, independent of any ABI stability guarantees.
There is also the #1 Kernel Rule: "we do not break users."
Booting a different version of the kernel is a core functionality of kexec. It is widely used to deploy new kernels or revert to older ones. Breaking this functionality is a show-stopper for most, if not all, hyperscalers.
This specific change may not be a show-stopper as CoCo deployment is not widespread enough to be noticed yet.
The notion that nobody promised that you can kexec into a different kernel is absurd. It is used everywhere.
> > > > Well, it certainly works for me. > > > > Unless you folks come-a-runnin' later screaming it broke some use case of > > yours. > > Heh, not me, but likely some of the CoCo folks regarding this specific use > case (kexec in a confidential VM). > > > And then we're back to what I've been preaching on this thread from the > > very beginning: having a common agreement on what ABI Linux enforces. > > Right. Maybe Kiryl knows more about this specific case as he brought up that > these structures are versioned.
I am not involved in the deployment of CoCo VMs, but I don't believe it is specifically about CoCo or the kexec ABI. I think it is more about the boot protocol. Kexec is one way to boot the kernel.
Should we consider the EFI configuration tables format as part of the boot protocol? I believe the answer is "yes," at least for some of them, like LINUX_EFI_INITRD_MEDIA_GUID.
I also think LINUX_EFI_UNACCEPTED_MEM_TABLE_GUID should be considered in the same way.
Ard, do you have any comments on this?
-- Kiryl Shutsemau / Kirill A. Shutemov
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