liveupdate: Rework KHO for in-kernel users & Fix memory corruption

From:		Pasha Tatashin <pasha.tatashin-AT-soleen.com>
To:		akpm-AT-linux-foundation.org, brauner-AT-kernel.org, corbet-AT-lwn.net, graf-AT-amazon.com, jgg-AT-ziepe.ca, linux-kernel-AT-vger.kernel.org, linux-kselftest-AT-vger.kernel.org, linux-mm-AT-kvack.org, masahiroy-AT-kernel.org, ojeda-AT-kernel.org, pasha.tatashin-AT-soleen.com, pratyush-AT-kernel.org, rdunlap-AT-infradead.org, rppt-AT-kernel.org, tj-AT-kernel.org, jasonmiu-AT-google.com, dmatlack-AT-google.com, skhawaja-AT-google.com
Subject:		[PATCH v6 00/10] liveupdate: Rework KHO for in-kernel users & Fix memory corruption
Date:		Sat, 18 Oct 2025 13:17:46 -0400
Message-ID:		<20251018171756.1724191-1-pasha.tatashin@soleen.com>
Archive-link:		Article

This series addresses comments and combines into one the two
series [1] and [2], and adds review-bys.

This series refactors the KHO framework to better support in-kernel
users like the upcoming LUO. The current design, which relies on a
notifier chain and debugfs for control, is too restrictive for direct
programmatic use.

The core of this rework is the removal of the notifier chain in favor of
a direct registration API. This decouples clients from the shutdown-time
finalization sequence, allowing them to manage their preserved state
more flexibly and at any time.

Also, this series fixes a memory corruption bug in KHO that occurs when
KFENCE is enabled.

The root cause is that KHO metadata, allocated via kzalloc(), can be
randomly serviced by kfence_alloc(). When a kernel boots via KHO, the
early memblock allocator is restricted to a "scratch area". This forces
the KFENCE pool to be allocated within this scratch area, creating a
conflict. If KHO metadata is subsequently placed in this pool, it gets
corrupted during the next kexec operation.

[1] https://lore.kernel.org/all/20251007033100.836886-1-pasha...
[2] https://lore.kernel.org/all/20251015053121.3978358-1-pash...

Mike Rapoport (Microsoft) (1):
  kho: drop notifiers

Pasha Tatashin (9):
  kho: allow to drive kho from within kernel
  kho: make debugfs interface optional
  kho: add interfaces to unpreserve folios and page ranes
  kho: don't unpreserve memory during abort
  liveupdate: kho: move to kernel/liveupdate
  kho: move kho debugfs directory to liveupdate
  liveupdate: kho: warn and fail on metadata or preserved memory in
    scratch area
  liveupdate: kho: Increase metadata bitmap size to PAGE_SIZE
  liveupdate: kho: allocate metadata directly from the buddy allocator

 Documentation/core-api/kho/concepts.rst     |   2 +-
 MAINTAINERS                                 |   3 +-
 include/linux/kexec_handover.h              |  53 +-
 init/Kconfig                                |   2 +
 kernel/Kconfig.kexec                        |  15 -
 kernel/Makefile                             |   2 +-
 kernel/liveupdate/Kconfig                   |  38 ++
 kernel/liveupdate/Makefile                  |   5 +
 kernel/{ => liveupdate}/kexec_handover.c    | 588 +++++++++-----------
 kernel/liveupdate/kexec_handover_debug.c    |  25 +
 kernel/liveupdate/kexec_handover_debugfs.c  | 216 +++++++
 kernel/liveupdate/kexec_handover_internal.h |  56 ++
 lib/test_kho.c                              |  30 +-
 mm/memblock.c                               |  62 +--
 tools/testing/selftests/kho/init.c          |   2 +-
 tools/testing/selftests/kho/vmtest.sh       |   1 +
 16 files changed, 645 insertions(+), 455 deletions(-)
 create mode 100644 kernel/liveupdate/Kconfig
 create mode 100644 kernel/liveupdate/Makefile
 rename kernel/{ => liveupdate}/kexec_handover.c (78%)
 create mode 100644 kernel/liveupdate/kexec_handover_debug.c
 create mode 100644 kernel/liveupdate/kexec_handover_debugfs.c
 create mode 100644 kernel/liveupdate/kexec_handover_internal.h


base-commit: f406055cb18c6e299c4a783fc1effeb16be41803
-- 
2.51.0.915.g61a8936c21-goog