This v2 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 [1] 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/rfc-v2 Changelog from v1: - Control Interface: Shifted from sysfs-based control (/sys/kernel/liveupdate/{prepare,finish}) to an ioctl interface (/dev/liveupdate). Sysfs is now primarily for monitoring the state. - Event/State Renaming: LIVEUPDATE_REBOOT event/phase is now LIVEUPDATE_FREEZE. - FD Preservation: A new component for preserving file descriptors. Subsystem Registration: A formal mechanism for kernel subsystems to participate. - Device Layer: removed device list handling from this series, it is going to be added separately. - Selftests: Kernel-side selftest hooks and userspace selftests are now included. KHO Enhancements: - KHO debugfs became optional, and kernel APIs for finalize/abort were added (driven by LUO's needs). - KHO unpreserve functions were also added. What is Live Update? Live Update is a specialized reboot process where selected kernel resources (memory, file descriptors, and eventually devices) are kept operational or their state preserved across a kernel transition (e.g., via kexec). For certain resources, DMA and interrupt activity might continue with minimal interruption during the kernel reboot. LUO v2 Overview: LUO v2 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. Example WIP for memfd preservation can be found here [2]. 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. [1] https://lore.kernel.org/all/20250509074635.3187114-1-changyuanl@xxxxxxxxxx https://github.com/googleprodkernel/linux-liveupdate/tree/luo/kho-v8 [2] https://github.com/googleprodkernel/linux-liveupdate/tree/luo/memfd-v0.1 RFC v1: https://lore.kernel.org/all/20250320024011.2995837-1-pasha.tatashin@xxxxxxxxxx Changyuan Lyu (1): kho: add kho_unpreserve_folio/phys Pasha Tatashin (15): kho: make debugfs interface optional kho: allow to drive kho from within kernel luo: luo_core: Live Update Orchestrator luo: luo_core: integrate with KHO luo: luo_subsystems: add subsystem registration luo: luo_subsystems: implement subsystem callbacks luo: luo_files: add infrastructure for FDs luo: luo_files: implement file systems callbacks luo: luo_ioctl: add ioctl interface luo: luo_sysfs: add sysfs state monitoring reboot: call liveupdate_reboot() before kexec luo: add selftests for subsystems un/registration selftests/liveupdate: add subsystem/state tests docs: add luo documentation MAINTAINERS: add liveupdate entry .../ABI/testing/sysfs-kernel-liveupdate | 51 ++ Documentation/admin-guide/index.rst | 1 + Documentation/admin-guide/liveupdate.rst | 62 ++ .../userspace-api/ioctl/ioctl-number.rst | 1 + MAINTAINERS | 14 +- drivers/misc/Kconfig | 1 + drivers/misc/Makefile | 1 + drivers/misc/liveupdate/Kconfig | 60 ++ drivers/misc/liveupdate/Makefile | 7 + drivers/misc/liveupdate/luo_core.c | 547 +++++++++++++++ drivers/misc/liveupdate/luo_files.c | 664 ++++++++++++++++++ drivers/misc/liveupdate/luo_internal.h | 59 ++ drivers/misc/liveupdate/luo_ioctl.c | 203 ++++++ drivers/misc/liveupdate/luo_selftests.c | 283 ++++++++ drivers/misc/liveupdate/luo_selftests.h | 23 + drivers/misc/liveupdate/luo_subsystems.c | 413 +++++++++++ drivers/misc/liveupdate/luo_sysfs.c | 92 +++ include/linux/kexec_handover.h | 27 + include/linux/liveupdate.h | 214 ++++++ include/uapi/linux/liveupdate.h | 324 +++++++++ kernel/Kconfig.kexec | 10 + kernel/Makefile | 1 + kernel/kexec_handover.c | 343 +++------ kernel/kexec_handover_debug.c | 237 +++++++ kernel/kexec_handover_internal.h | 74 ++ kernel/reboot.c | 4 + 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 | 440 ++++++++++++ 31 files changed, 3933 insertions(+), 238 deletions(-) create mode 100644 Documentation/ABI/testing/sysfs-kernel-liveupdate create mode 100644 Documentation/admin-guide/liveupdate.rst create mode 100644 drivers/misc/liveupdate/Kconfig create mode 100644 drivers/misc/liveupdate/Makefile create mode 100644 drivers/misc/liveupdate/luo_core.c create mode 100644 drivers/misc/liveupdate/luo_files.c create mode 100644 drivers/misc/liveupdate/luo_internal.h create mode 100644 drivers/misc/liveupdate/luo_ioctl.c create mode 100644 drivers/misc/liveupdate/luo_selftests.c create mode 100644 drivers/misc/liveupdate/luo_selftests.h create mode 100644 drivers/misc/liveupdate/luo_subsystems.c create mode 100644 drivers/misc/liveupdate/luo_sysfs.c create mode 100644 include/linux/liveupdate.h create mode 100644 include/uapi/linux/liveupdate.h create mode 100644 kernel/kexec_handover_debug.c create mode 100644 kernel/kexec_handover_internal.h 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 -- 2.49.0.1101.gccaa498523-goog
