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Message-ID: <20250625235607.GK369@kvack.org>
Date: Wed, 25 Jun 2025 19:56:07 -0400
From: Benjamin LaHaise <bcrl@...ck.org>
To: "pasha.tatashin" <pasha.tatashin@...een.com>
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Subject: Re: [PATCH v1 00/32] Live Update Orchestrator
On Wed, Jun 25, 2025 at 07:44:12PM -0400, pasha.tatashin wrote:
> 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.
I'm close to kicking all the @gmail.com subscribers off the mailing lists
given how bad this is getting. My general advice to anyone posting to
mailing lists these days is to assume that anyone reading email via any of
Google's service isn't going to see your mailing list posts. It keeps
getting worse, and nobody at the platform companies seems to care.
-ben
> 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."
>
--
"Thought is the essence of where you are now."
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