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

[David Hildenbrand (Red Hat)]

On 12/1/25 12:12, Borislav Petkov wrote:
> On Mon, Dec 01, 2025 at 10:18:37AM +0100, David Hildenbrand (Red Hat) wrote:
> > Makes sense to me, especially for confidential VMs where we pass such
> > kernel-managed data from the old to the new kernel.
>
> It shouldn't matter, right?
>
> I think the question is whether the kernel should agree to the software
> contract (/eyeroll) to keep the kernel ABI compatible wrt kexec.
>
> And I don't think we have agreed to that AFAIK.

I think we are in agreement: from what I recall, this software contract used to be
rather simple and stable.

Looking into the details, I guess it's all about

$ grep "define LINUX_EFI_" include/linux/efi.h
#define LINUX_EFI_CRASH_GUID                    EFI_GUID(0xcfc8fc79, 0xbe2e, 0x4ddc,  0x97, 0xf0, 0x9f, 0x98, 0xbf, 0xe2, 0x98, 0xa0)
#define LINUX_EFI_SCREEN_INFO_TABLE_GUID        EFI_GUID(0xe03fc20a, 0x85dc, 0x406e,  0xb9, 0x0e, 0x4a, 0xb5, 0x02, 0x37, 0x1d, 0x95)
#define LINUX_EFI_ARM_CPU_STATE_TABLE_GUID      EFI_GUID(0xef79e4aa, 0x3c3d, 0x4989,  0xb9, 0x02, 0x07, 0xa9, 0x43, 0xe5, 0x50, 0xd2)
#define LINUX_EFI_LOADER_ENTRY_GUID             EFI_GUID(0x4a67b082, 0x0a4c, 0x41cf,  0xb6, 0xc7, 0x44, 0x0b, 0x29, 0xbb, 0x8c, 0x4f)
#define LINUX_EFI_RANDOM_SEED_TABLE_GUID        EFI_GUID(0x1ce1e5bc, 0x7ceb, 0x42f2,  0x81, 0xe5, 0x8a, 0xad, 0xf1, 0x80, 0xf5, 0x7b)
#define LINUX_EFI_TPM_EVENT_LOG_GUID            EFI_GUID(0xb7799cb0, 0xeca2, 0x4943,  0x96, 0x67, 0x1f, 0xae, 0x07, 0xb7, 0x47, 0xfa)
#define LINUX_EFI_MEMRESERVE_TABLE_GUID         EFI_GUID(0x888eb0c6, 0x8ede, 0x4ff5,  0xa8, 0xf0, 0x9a, 0xee, 0x5c, 0xb9, 0x77, 0xc2)
#define LINUX_EFI_INITRD_MEDIA_GUID             EFI_GUID(0x5568e427, 0x68fc, 0x4f3d,  0xac, 0x74, 0xca, 0x55, 0x52, 0x31, 0xcc, 0x68)
#define LINUX_EFI_MOK_VARIABLE_TABLE_GUID       EFI_GUID(0xc451ed2b, 0x9694, 0x45d3,  0xba, 0xba, 0xed, 0x9f, 0x89, 0x88, 0xa3, 0x89)
#define LINUX_EFI_COCO_SECRET_AREA_GUID         EFI_GUID(0xadf956ad, 0xe98c, 0x484c,  0xae, 0x11, 0xb5, 0x1c, 0x7d, 0x33, 0x64, 0x47)
#define LINUX_EFI_BOOT_MEMMAP_GUID              EFI_GUID(0x800f683f, 0xd08b, 0x423a,  0xa2, 0x93, 0x96, 0x5c, 0x3c, 0x6f, 0xe2, 0xb4)
#define LINUX_EFI_UNACCEPTED_MEM_TABLE_GUID     EFI_GUID(0xd5d1de3c, 0x105c, 0x44f9,  0x9e, 0xa9, 0xbc, 0xef, 0x98, 0x12, 0x00, 0x31)
#define LINUX_EFI_LOADED_IMAGE_FIXED_GUID       EFI_GUID(0xf5a37b6d, 0x3344, 0x42a5,  0xb6, 0xbb, 0x97, 0x86, 0x48, 0xc1, 0x89, 0x0a)

Likely the format of these section stayed unchanged over the years.

--
Cheers

David