Re: [PATCH v4 00/19] kho, liveupdate: Add feature header for fine-grained ABI compatibility

[tarunsahu@google.com]

"Pasha Tatashin" <pasha.tatashin@soleen.com> writes:

> On Tue Nov 10, 2026 at 12:01 AM EST, Tarun Sahu wrote:
>> This v4 of feature flags support for LUO and KHO is no longer an RFC.
...skip
>>
>> Each serialized structure is preceded in memory by struct kho_ser_hdr
>> and registered via DECLARE_KHO_SER(name, payload_size, nr_required,
>> nr_optional). Both struct kho_kexec_metadata and struct pci_dev_ser are
>> explicitly marked with __aligned(8) because their largest member is a
>> 32-bit integer, and 8-byte alignment is required by DECLARE_KHO_SER() so
>
> I do not believe we need __aligned(8), because the struct immediately 
> follows the newly introduced kho_ser_hdr, which is 8-byte aligned. 
> However, we should verify that the combined size (header + payload) 
> is 8-byte aligned.

Yes, we can check total size alignment and remove the __aligned(8). I
will update it.

~Tarun

>
>> trailing feature payloads remain 8-byte aligned across 32-bit and 64-bit
>> kernels.
>>
>> Also, Introduce DECLARE_KHO_SER_HDR(ser_name, fhdr) which is just the
>> wrapper for struct kho_ser_hdr fhdr, This makes it clear
>> To which ser_name, this fhdr belongs to.
>>
>>
>> Series structure:
>>   - Patch 1 removes __packed from KHO, LUO, and memfd ABI structures and
>>     asserts their natural size and 8-byte alignment under CONFIG_64BIT.
>>   - Patch 2 records entry_size in struct kho_block_header_ser so the
>>     incoming kernel derives the entry stride from the block header.
>>   - Patch 3 converts callers that embedded struct kho_vmalloc by value
>>     (memfd_luo and test_kho) to reference it via DECLARE_KHOSER_PTR so
>>     struct kho_vmalloc can grow independently.
>>   - Patch 4 converts struct luo_session_ser to reference
>>     struct luo_file_set_ser via DECLARE_KHOSER_PTR instead of embedding
>>     it by value so both structures can grow independently.
>>   - Patch 5 introduces struct kho_ser_hdr, DECLARE_KHO_SER(),
>>     DECLARE_KHO_SER_HDR(), and the serialization/validation helpers in
>>     include/linux/kho/abi/feature.h.
>>   - Patches 6-18 add the feature header to each of the 13 KHO, LUO, PCI,
>>     and memfd serialized structures in independent patches.
>>   - Patch 19 adds a KUnit test suite (kho_feature) covering the feature
>>     header helpers.
>>
>> [1] https://lore.kernel.org/all/20260903023452.721732-1-loganodell@google.com/
>> [2] https://lore.kernel.org/all/20261021152527.375070-1-tarunsahu@google.com/
>> [3] https://lore.kernel.org/all/20261026174217.603114-1-tarunsahu@google.com/
>>
>> Tarun Sahu (19):
>>   liveupdate, kho: Remove __packed from KHO, LUO and memfd ABI
>>     structures
>>   kho: block: Record the entry size in the block header
>>   kho, memfd_luo: Reference struct kho_vmalloc via serialized pointer
>>   liveupdate: Reference struct luo_file_set_ser via serialized pointer
>>   kho: Add feature header for fine-grained ABI compatibility
>>   kho: kexec_metadata: Add the feature header
>>   kho: vmalloc: Add the feature header
>>   kho: block: Add the feature header to blocks
>>   liveupdate: Add feature header to struct luo_ser
>>   liveupdate: Add feature header to struct luo_session_ser
>>   liveupdate: Add feature header to struct luo_file_set_ser
>>   liveupdate: Add feature header to struct luo_file_ser
>>   liveupdate: Add feature header to struct luo_flb_header_ser
>>   liveupdate: Add feature header to struct luo_flb_ser
>>   PCI: liveupdate: Add feature header to struct pci_ser
>>   PCI: liveupdate: Add feature header to struct pci_dev_ser
>>   mm: memfd_luo: Add feature header to struct memfd_luo_ser
>>   mm: memfd_luo: Add feature header to struct memfd_luo_folio_ser
>>   kho: Add KUnit test for the feature header helpers
>>
>>  MAINTAINERS                            |   1 +
>>  drivers/pci/liveupdate.c               |  99 +++----
>>  include/linux/kexec_handover.h         |  15 +-
>>  include/linux/kho/abi/block.h          |  21 +-
>>  include/linux/kho/abi/feature.h        | 372 +++++++++++++++++++++++++
>>  include/linux/kho/abi/kexec_handover.h |  11 +-
>>  include/linux/kho/abi/kexec_metadata.h |  17 +-
>>  include/linux/kho/abi/luo.h            | 102 ++++---
>>  include/linux/kho/abi/memfd.h          |  27 +-
>>  include/linux/kho/abi/pci.h            |  66 ++---
>>  include/linux/kho_block.h              |   8 +-
>>  kernel/liveupdate/kexec_handover.c     |  98 ++++---
>>  kernel/liveupdate/kho_block.c          | 172 +++++++++---
>>  kernel/liveupdate/luo_core.c           |  43 +--
>>  kernel/liveupdate/luo_file.c           |  58 ++--
>>  kernel/liveupdate/luo_flb.c            |  69 +++--
>>  kernel/liveupdate/luo_internal.h       |   9 +-
>>  kernel/liveupdate/luo_session.c        |  55 +++-
>>  lib/Kconfig.debug                      |  13 +
>>  lib/test_kho.c                         |  38 ++-
>>  lib/tests/Makefile                     |   1 +
>>  lib/tests/kho_feature_kunit.c          | 184 ++++++++++++
>>  mm/memfd_luo.c                         | 183 ++++++++----
>>  23 files changed, 1271 insertions(+), 391 deletions(-)
>>  create mode 100644 include/linux/kho/abi/feature.h
>>  create mode 100644 lib/tests/kho_feature_kunit.c
>
> -- 
> Pasha