On Fri, Aug 8, 2025 at 12:07 PM David Hildenbrand <david@xxxxxxxxxx> wrote: > > 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. Hi David, Yes, I should update the cover letter to include memfd preservation work. > I suggest sending that part out separately, so Hugh actually spots this. > (is he even CC'ed?) +cc hughd@xxxxxxxxxx While MM list is CCed, you are right, I have not specifically CCed shmem maintainers. This will be fixed in the next revision. Thank you, Pasha
