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Message-ID: <CA+CK2bAsz4Zz2_Kp8QMKxG5taY52ykhhykROd0di85ax5eeOrw@mail.gmail.com>
Date: Wed, 25 Jun 2025 19:44:12 -0400
From: "pasha.tatashin" <pasha.tatashin@...een.com>
To: Benjamin LaHaise <bcrl@...ck.org>
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Subject: Re: [PATCH v1 00/32] Live Update Orchestrator
On Wed, Jun 25, 2025 at 7:26 PM Benjamin LaHaise <bcrl@...ck.org> wrote:
>
> 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)
This is extremely annoying, I will need to figure out why this is
happening. soleen.com uses google workspace.
Pasha
>
> 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@soleen.com
> > RFC v2: https://lore.kernel.org/all/20250515182322.117840-1-pasha.tatashin@soleen.com/
> >
> > 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."
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