On 07.08.25 03:44, 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/v3 Changelog from v2: - Addressed comments from Mike Rapoport and Jason Gunthorpe - Only one user agent (LiveupdateD) can open /dev/liveupdate - Release all preserved resources if /dev/liveupdate closes before reboot. - With the above changes, sessions are not needed, and should be maintained by the user-agent itself, so removed support for sessions. - Added support for changing per-FD state (i.e. some FDs can be prepared or finished before the global transition. - All IOCTLs now follow iommufd/fwctl extendable design. - Replaced locks with guards - Added a callback for registered subsystems to be notified during boot: ops->boot(). - Removed args from callbacks, instead use container_of() to carry context specific data (see luo_selftests.c for example). - removed patches for luolib, they are going to be introduced in a separate repository. 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. v2: https://lore.kernel.org/all/20250723144649.1696299-1-pasha.tatashin@xxxxxxxxxx v1: https://lore.kernel.org/all/20250625231838.1897085-1-pasha.tatashin@xxxxxxxxxx RFC v2: https://lore.kernel.org/all/20250515182322.117840-1-pasha.tatashin@xxxxxxxxxx RFC v1: https://lore.kernel.org/all/20250320024011.2995837-1-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 (23): 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: luo_ioctl: 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 userpsace interface liveupdate: luo_files: luo_ioctl: Unregister all FDs on device close liveupdate: luo_files: luo_ioctl: Add ioctls for per-file state management liveupdate: luo_sysfs: add sysfs state monitoring reboot: call liveupdate_reboot() before kexec 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 (5): 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
It's not clear from the description why these mm shmem changes are buried in this patch set. It's not even described above in the patch description.
I suggest sending that part out separately, so Hugh actually spots this. (is he even CC'ed?) -- Cheers, David / dhildenb
