FYI: Every one of your emails to the list for this series was bounced by all the recipients using @gmail.com email addresses. -ben (owner-linux-mm) On Wed, Jun 25, 2025 at 11:17:47PM +0000, Pasha Tatashin wrote: > This series introduces the LUO, a kernel subsystem designed to > facilitate live kernel updates with minimal downtime, > particularly in cloud delplyoments aiming to update without fully > disrupting running virtual machines. > > This series builds upon KHO framework by adding programmatic > control over KHO's lifecycle and leveraging KHO for persisting LUO's > own metadata across the kexec boundary. The git branch for this series > can be found at: > > https://github.com/googleprodkernel/linux-liveupdate/tree/luo/v1 > > Changelog from rfc-v2: > - Addressed review comments from Mike Rapoport, Pratyush Yadav, > David Matlack > - Moved everything under kernel/liveupdate including KHO. > - Added a number fixes to KHO that were discovered. > - luo_files is not a registred as a subsystem. > - Added sessions support to preserved files. > - Added support for memfd (Pratyush Yadav) > - Added libluo (proposed as RFC) (Pratyush Yadav) > - Removed notifiers from KHO (Mike Rapoport) > > What is Live Update? > Live Update is a kexec based reboot process where selected kernel > resources (memory, file descriptors, and eventually devices) are kept > operational or their state preserved across a kernel transition. For > certain resources, DMA and interrupt activity might continue with > minimal interruption during the kernel reboot. > > LUO provides a framework for coordinating live updates. It features: > State Machine: Manages the live update process through states: > NORMAL, PREPARED, FROZEN, UPDATED. > > KHO Integration: > > LUO programmatically drives KHO's finalization and abort sequences. > KHO's debugfs interface is now optional configured via > CONFIG_KEXEC_HANDOVER_DEBUG. > > LUO preserves its own metadata via KHO's kho_add_subtree and > kho_preserve_phys() mechanisms. > > Subsystem Participation: A callback API liveupdate_register_subsystem() > allows kernel subsystems (e.g., KVM, IOMMU, VFIO, PCI) to register > handlers for LUO events (PREPARE, FREEZE, FINISH, CANCEL) and persist a > u64 payload via the LUO FDT. > > File Descriptor Preservation: Infrastructure > liveupdate_register_filesystem, luo_register_file, luo_retrieve_file to > allow specific types of file descriptors (e.g., memfd, vfio) to be > preserved and restored. > > Handlers for specific file types can be registered to manage their > preservation and restoration, storing a u64 payload in the LUO FDT. > > User-space Interface: > > ioctl (/dev/liveupdate): The primary control interface for > triggering LUO state transitions (prepare, freeze, finish, cancel) > and managing the preservation/restoration of file descriptors. > Access requires CAP_SYS_ADMIN. > > sysfs (/sys/kernel/liveupdate/state): A read-only interface for > monitoring the current LUO state. This allows userspace services to > track progress and coordinate actions. > > Selftests: Includes kernel-side hooks and userspace selftests to > verify core LUO functionality, particularly subsystem registration and > basic state transitions. > > LUO State Machine and Events: > > NORMAL: Default operational state. > PREPARED: Initial preparation complete after LIVEUPDATE_PREPARE > event. Subsystems have saved initial state. > FROZEN: Final "blackout window" state after LIVEUPDATE_FREEZE > event, just before kexec. Workloads must be suspended. > UPDATED: Next kernel has booted via live update. Awaiting restoration > and LIVEUPDATE_FINISH. > > Events: > LIVEUPDATE_PREPARE: Prepare for reboot, serialize state. > LIVEUPDATE_FREEZE: Final opportunity to save state before kexec. > LIVEUPDATE_FINISH: Post-reboot cleanup in the next kernel. > LIVEUPDATE_CANCEL: Abort prepare or freeze, revert changes. > > RFC v1: https://lore.kernel.org/all/20250320024011.2995837-1-pasha.tatashin@xxxxxxxxxx > RFC v2: https://lore.kernel.org/all/20250515182322.117840-1-pasha.tatashin@xxxxxxxxxx/ > > Changyuan Lyu (1): > kho: add interfaces to unpreserve folios and physical memory ranges > > Mike Rapoport (Microsoft) (1): > kho: drop notifiers > > Pasha Tatashin (22): > kho: init new_physxa->phys_bits to fix lockdep > kho: mm: Don't allow deferred struct page with KHO > kho: warn if KHO is disabled due to an error > kho: allow to drive kho from within kernel > kho: make debugfs interface optional > kho: don't unpreserve memory during abort > liveupdate: kho: move to kernel/liveupdate > liveupdate: luo_core: Live Update Orchestrator > liveupdate: luo_core: integrate with KHO > liveupdate: luo_subsystems: add subsystem registration > liveupdate: luo_subsystems: implement subsystem callbacks > liveupdate: luo_files: add infrastructure for FDs > liveupdate: luo_files: implement file systems callbacks > liveupdate: luo_ioctl: add ioctl interface > liveupdate: luo_sysfs: add sysfs state monitoring > reboot: call liveupdate_reboot() before kexec > liveupdate: luo_files: luo_ioctl: session-based file descriptor > tracking > kho: move kho debugfs directory to liveupdate > liveupdate: add selftests for subsystems un/registration > selftests/liveupdate: add subsystem/state tests > docs: add luo documentation > MAINTAINERS: add liveupdate entry > > Pratyush Yadav (8): > mm: shmem: use SHMEM_F_* flags instead of VM_* flags > mm: shmem: allow freezing inode mapping > mm: shmem: export some functions to internal.h > luo: allow preserving memfd > docs: add documentation for memfd preservation via LUO > tools: introduce libluo > libluo: introduce luoctl > libluo: add tests > > .../ABI/testing/sysfs-kernel-liveupdate | 51 + > Documentation/admin-guide/index.rst | 1 + > Documentation/admin-guide/liveupdate.rst | 16 + > Documentation/core-api/index.rst | 1 + > Documentation/core-api/kho/concepts.rst | 2 +- > Documentation/core-api/liveupdate.rst | 57 ++ > Documentation/mm/index.rst | 1 + > Documentation/mm/memfd_preservation.rst | 138 +++ > Documentation/userspace-api/index.rst | 1 + > .../userspace-api/ioctl/ioctl-number.rst | 2 + > Documentation/userspace-api/liveupdate.rst | 25 + > MAINTAINERS | 20 +- > include/linux/kexec_handover.h | 53 +- > include/linux/liveupdate.h | 235 +++++ > include/linux/shmem_fs.h | 23 + > include/uapi/linux/liveupdate.h | 265 +++++ > init/Kconfig | 2 + > kernel/Kconfig.kexec | 14 - > kernel/Makefile | 2 +- > kernel/liveupdate/Kconfig | 90 ++ > kernel/liveupdate/Makefile | 13 + > kernel/{ => liveupdate}/kexec_handover.c | 556 +++++----- > kernel/liveupdate/kexec_handover_debug.c | 222 ++++ > kernel/liveupdate/kexec_handover_internal.h | 45 + > kernel/liveupdate/luo_core.c | 525 ++++++++++ > kernel/liveupdate/luo_files.c | 946 ++++++++++++++++++ > kernel/liveupdate/luo_internal.h | 47 + > kernel/liveupdate/luo_ioctl.c | 192 ++++ > kernel/liveupdate/luo_selftests.c | 344 +++++++ > kernel/liveupdate/luo_selftests.h | 84 ++ > kernel/liveupdate/luo_subsystems.c | 420 ++++++++ > kernel/liveupdate/luo_sysfs.c | 92 ++ > kernel/reboot.c | 4 + > mm/Makefile | 1 + > mm/internal.h | 6 + > mm/memblock.c | 56 +- > mm/memfd_luo.c | 501 ++++++++++ > mm/shmem.c | 46 +- > tools/lib/luo/LICENSE | 165 +++ > tools/lib/luo/Makefile | 45 + > tools/lib/luo/README.md | 166 +++ > tools/lib/luo/cli/.gitignore | 1 + > tools/lib/luo/cli/Makefile | 18 + > tools/lib/luo/cli/luoctl.c | 178 ++++ > tools/lib/luo/include/libluo.h | 128 +++ > tools/lib/luo/include/liveupdate.h | 265 +++++ > tools/lib/luo/libluo.c | 203 ++++ > tools/lib/luo/tests/.gitignore | 1 + > tools/lib/luo/tests/Makefile | 18 + > tools/lib/luo/tests/test.c | 848 ++++++++++++++++ > tools/testing/selftests/Makefile | 1 + > tools/testing/selftests/liveupdate/.gitignore | 1 + > tools/testing/selftests/liveupdate/Makefile | 7 + > tools/testing/selftests/liveupdate/config | 6 + > .../testing/selftests/liveupdate/liveupdate.c | 356 +++++++ > 55 files changed, 7091 insertions(+), 415 deletions(-) > create mode 100644 Documentation/ABI/testing/sysfs-kernel-liveupdate > create mode 100644 Documentation/admin-guide/liveupdate.rst > create mode 100644 Documentation/core-api/liveupdate.rst > create mode 100644 Documentation/mm/memfd_preservation.rst > create mode 100644 Documentation/userspace-api/liveupdate.rst > create mode 100644 include/linux/liveupdate.h > create mode 100644 include/uapi/linux/liveupdate.h > create mode 100644 kernel/liveupdate/Kconfig > create mode 100644 kernel/liveupdate/Makefile > rename kernel/{ => liveupdate}/kexec_handover.c (74%) > create mode 100644 kernel/liveupdate/kexec_handover_debug.c > create mode 100644 kernel/liveupdate/kexec_handover_internal.h > create mode 100644 kernel/liveupdate/luo_core.c > create mode 100644 kernel/liveupdate/luo_files.c > create mode 100644 kernel/liveupdate/luo_internal.h > create mode 100644 kernel/liveupdate/luo_ioctl.c > create mode 100644 kernel/liveupdate/luo_selftests.c > create mode 100644 kernel/liveupdate/luo_selftests.h > create mode 100644 kernel/liveupdate/luo_subsystems.c > create mode 100644 kernel/liveupdate/luo_sysfs.c > create mode 100644 mm/memfd_luo.c > create mode 100644 tools/lib/luo/LICENSE > create mode 100644 tools/lib/luo/Makefile > create mode 100644 tools/lib/luo/README.md > create mode 100644 tools/lib/luo/cli/.gitignore > create mode 100644 tools/lib/luo/cli/Makefile > create mode 100644 tools/lib/luo/cli/luoctl.c > create mode 100644 tools/lib/luo/include/libluo.h > create mode 100644 tools/lib/luo/include/liveupdate.h > create mode 100644 tools/lib/luo/libluo.c > create mode 100644 tools/lib/luo/tests/.gitignore > create mode 100644 tools/lib/luo/tests/Makefile > create mode 100644 tools/lib/luo/tests/test.c > create mode 100644 tools/testing/selftests/liveupdate/.gitignore > create mode 100644 tools/testing/selftests/liveupdate/Makefile > create mode 100644 tools/testing/selftests/liveupdate/config > create mode 100644 tools/testing/selftests/liveupdate/liveupdate.c > > -- > 2.50.0.727.gbf7dc18ff4-goog > -- "Thought is the essence of where you are now."
