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Author SHA1 Message Date
Pratyush Yadav (Google) ec7c0b1a0d kho: expose kho_scratch_overlap() to kexec_handover.h 
Support for discovering memory blocks with no preserved memory will be
added in coming patches. These areas will also be marked as scratch to
allow allocations from them. Memblock will switch to looking through the
scratch array to decide the right migratetype.

Expose kho_scratch_overlap() to KHO users. Since it is now used by
non-debug code, move it out of kexec_handover_debug.c and into
kexec_handover.c. Gate the overlap checks in kho_preserve_folio() and
kho_preserve_pages() by IS_ENABLED(CONFIG_KEXEC_HANDOVER_DEBUG) instead.

Since kexec_handover_debug.c is now empty, delete it.

Add a stub for kho_scratch_overlap() to memblock tests to make sure it
compiles. It will be used in memblock by a coming commit.

No functional changes.

Signed-off-by: Pratyush Yadav (Google) <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Mike Rapoport (Microsoft) <[email protected]>
 2026-08-04 09:23:05 +03:00
Pasha Tatashin 0349ff2887 kho: add support for linked-block serialization 
Introduce a linked-block serialization mechanism for state handover.

Previously, LUO used contiguous memory blocks for serializing sessions
and files, which imposed limits on the total number of items that could
be preserved across a live update.

This commit adds the infrastructure for a more flexible, block-based
approach where serialized data is stored in a chain of linked blocks.
This is a generic KHO serialization block infrastructure that can be
used by multiple subsystems.

Signed-off-by: Pasha Tatashin <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Mike Rapoport (Microsoft) <[email protected]>
 2026-06-03 21:15:46 +03:00
Pasha Tatashin cab056f2aa liveupdate: luo_flb: introduce File-Lifecycle-Bound global state 
Introduce a mechanism for managing global kernel state whose lifecycle is
tied to the preservation of one or more files.  This is necessary for
subsystems where multiple preserved file descriptors depend on a single,
shared underlying resource.

An example is HugeTLB, where multiple file descriptors such as memfd and
guest_memfd may rely on the state of a single HugeTLB subsystem. 
Preserving this state for each individual file would be redundant and
incorrect.  The state should be preserved only once when the first file is
preserved, and restored/finished only once the last file is handled.

This patch introduces File-Lifecycle-Bound (FLB) objects to solve this
problem.  An FLB is a global, reference-counted object with a defined set
of operations:

- A file handler (struct liveupdate_file_handler) declares a dependency
  on one or more FLBs via a new registration function,
  liveupdate_register_flb().
- When the first file depending on an FLB is preserved, the FLB's
  .preserve() callback is invoked to save the shared global state. The
  reference count is then incremented for each subsequent file.
- Conversely, when the last file is unpreserved (before reboot) or
  finished (after reboot), the FLB's .unpreserve() or .finish() callback
  is invoked to clean up the global resource.

The implementation includes:

- A new set of ABI definitions (luo_flb_ser, luo_flb_head_ser) and a
  corresponding FDT node (luo-flb) to serialize the state of all active
  FLBs and pass them via Kexec Handover.
- Core logic in luo_flb.c to manage FLB registration, reference
  counting, and the invocation of lifecycle callbacks.
- An API (liveupdate_flb_get/_incoming/_outgoing) for other kernel
  subsystems to safely access the live object managed by an FLB, both
  before and after the live update.

This framework provides the necessary infrastructure for more complex
subsystems like IOMMU, VFIO, and KVM to integrate with the Live Update
Orchestrator.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Pasha Tatashin <[email protected]>
Cc: Alexander Graf <[email protected]>
Cc: David Gow <[email protected]>
Cc: David Matlack <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Mike Rapoport <[email protected]>
Cc: Petr Mladek <[email protected]>
Cc: Pratyush Yadav <[email protected]>
Cc: Samiullah Khawaja <[email protected]>
Cc: Tamir Duberstein <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
 2026-02-08 00:13:33 -08:00
Pasha Tatashin 7c722a7f44 liveupdate: luo_file: implement file systems callbacks 
This patch implements the core mechanism for managing preserved files
throughout the live update lifecycle.  It provides the logic to invoke the
file handler callbacks (preserve, unpreserve, freeze, unfreeze, retrieve,
and finish) at the appropriate stages.

During the reboot phase, luo_file_freeze() serializes the final metadata
for each file (handler compatible string, token, and data handle) into a
memory region preserved by KHO.  In the new kernel, luo_file_deserialize()
reconstructs the in-memory file list from this data, preparing the session
for retrieval.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Pasha Tatashin <[email protected]>
Reviewed-by: Mike Rapoport (Microsoft) <[email protected]>
Reviewed-by: Pratyush Yadav <[email protected]>
Tested-by: David Matlack <[email protected]>
Cc: Aleksander Lobakin <[email protected]>
Cc: Alexander Graf <[email protected]>
Cc: Alice Ryhl <[email protected]>
Cc: Andriy Shevchenko <[email protected]>
Cc: anish kumar <[email protected]>
Cc: Anna Schumaker <[email protected]>
Cc: Bartosz Golaszewski <[email protected]>
Cc: Bjorn Helgaas <[email protected]>
Cc: Borislav Betkov <[email protected]>
Cc: Chanwoo Choi <[email protected]>
Cc: Chen Ridong <[email protected]>
Cc: Chris Li <[email protected]>
Cc: Christian Brauner <[email protected]>
Cc: Daniel Wagner <[email protected]>
Cc: Danilo Krummrich <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: David Jeffery <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Guixin Liu <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Ilpo Järvinen <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Ira Weiny <[email protected]>
Cc: Jann Horn <[email protected]>
Cc: Jason Gunthorpe <[email protected]>
Cc: Jens Axboe <[email protected]>
Cc: Joanthan Cameron <[email protected]>
Cc: Joel Granados <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Lennart Poettering <[email protected]>
Cc: Leon Romanovsky <[email protected]>
Cc: Leon Romanovsky <[email protected]>
Cc: Lukas Wunner <[email protected]>
Cc: Marc Rutland <[email protected]>
Cc: Masahiro Yamada <[email protected]>
Cc: Matthew Maurer <[email protected]>
Cc: Miguel Ojeda <[email protected]>
Cc: Myugnjoo Ham <[email protected]>
Cc: Parav Pandit <[email protected]>
Cc: Pratyush Yadav <[email protected]>
Cc: Randy Dunlap <[email protected]>
Cc: Roman Gushchin <[email protected]>
Cc: Saeed Mahameed <[email protected]>
Cc: Samiullah Khawaja <[email protected]>
Cc: Song Liu <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: Stuart Hayes <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Thomas Gleinxer <[email protected]>
Cc: Thomas Weißschuh <[email protected]>
Cc: Vincent Guittot <[email protected]>
Cc: William Tu <[email protected]>
Cc: Yoann Congal <[email protected]>
Cc: Zhu Yanjun <[email protected]>
Cc: Zijun Hu <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
 2025-11-27 14:24:38 -08:00
Pasha Tatashin 0153094d03 liveupdate: luo_session: add sessions support 
Introduce concept of "Live Update Sessions" within the LUO framework.  LUO
sessions provide a mechanism to group and manage `struct file *` instances
(representing file descriptors) that need to be preserved across a
kexec-based live update.

Each session is identified by a unique name and acts as a container for
file objects whose state is critical to a userspace workload, such as a
virtual machine or a high-performance database, aiming to maintain their
functionality across a kernel transition.

This groundwork establishes the framework for preserving file-backed state
across kernel updates, with the actual file data preservation mechanisms
to be implemented in subsequent patches.

[[email protected]: fix use after free in luo_session_deserialize()]
  Link: https://lkml.kernel.org/r/c5dd637d7eed3a3be48c5e9fedb881596a3b1f5a.1764163896.git.dan.carpenter@linaro.org
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Pasha Tatashin <[email protected]>
Signed-off-by: Dan Carpenter <[email protected]>
Reviewed-by: Mike Rapoport (Microsoft) <[email protected]>
Reviewed-by: Pratyush Yadav <[email protected]>
Tested-by: David Matlack <[email protected]>
Cc: Aleksander Lobakin <[email protected]>
Cc: Alexander Graf <[email protected]>
Cc: Alice Ryhl <[email protected]>
Cc: Andriy Shevchenko <[email protected]>
Cc: anish kumar <[email protected]>
Cc: Anna Schumaker <[email protected]>
Cc: Bartosz Golaszewski <[email protected]>
Cc: Bjorn Helgaas <[email protected]>
Cc: Borislav Betkov <[email protected]>
Cc: Chanwoo Choi <[email protected]>
Cc: Chen Ridong <[email protected]>
Cc: Chris Li <[email protected]>
Cc: Christian Brauner <[email protected]>
Cc: Daniel Wagner <[email protected]>
Cc: Danilo Krummrich <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: David Jeffery <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Guixin Liu <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Ilpo Järvinen <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Ira Weiny <[email protected]>
Cc: Jann Horn <[email protected]>
Cc: Jason Gunthorpe <[email protected]>
Cc: Jens Axboe <[email protected]>
Cc: Joanthan Cameron <[email protected]>
Cc: Joel Granados <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Lennart Poettering <[email protected]>
Cc: Leon Romanovsky <[email protected]>
Cc: Leon Romanovsky <[email protected]>
Cc: Lukas Wunner <[email protected]>
Cc: Marc Rutland <[email protected]>
Cc: Masahiro Yamada <[email protected]>
Cc: Matthew Maurer <[email protected]>
Cc: Miguel Ojeda <[email protected]>
Cc: Myugnjoo Ham <[email protected]>
Cc: Parav Pandit <[email protected]>
Cc: Pratyush Yadav <[email protected]>
Cc: Randy Dunlap <[email protected]>
Cc: Roman Gushchin <[email protected]>
Cc: Saeed Mahameed <[email protected]>
Cc: Samiullah Khawaja <[email protected]>
Cc: Song Liu <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: Stuart Hayes <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Thomas Gleinxer <[email protected]>
Cc: Thomas Weißschuh <[email protected]>
Cc: Vincent Guittot <[email protected]>
Cc: William Tu <[email protected]>
Cc: Yoann Congal <[email protected]>
Cc: Zhu Yanjun <[email protected]>
Cc: Zijun Hu <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
 2025-11-27 14:24:38 -08:00
Pasha Tatashin 9e2fd062fa liveupdate: luo_core: Live Update Orchestrator 
Patch series "Live Update Orchestrator", v8.

This series introduces the Live Update Orchestrator, a kernel subsystem
designed to facilitate live kernel updates using a kexec-based reboot. 
This capability is critical for cloud environments, allowing hypervisors
to be updated with minimal downtime for running virtual machines.  LUO
achieves this by preserving the state of selected resources, such as
memory, devices and their dependencies, across the kernel transition.

As a key feature, this series includes support for preserving memfd file
descriptors, which allows critical in-memory data, such as guest RAM or
any other large memory region, to be maintained in RAM across the kexec
reboot.

The other series that use LUO, are VFIO [1], IOMMU [2], and PCI [3]
preservations.

Github repo of this series [4].

The core of LUO is a framework for managing the lifecycle of preserved
resources through a userspace-driven interface. Key features include:

- Session Management
  Userspace agent (i.e. luod [5]) creates named sessions, each
  represented by a file descriptor (via centralized agent that controls
  /dev/liveupdate). The lifecycle of all preserved resources within a
  session is tied to this FD, ensuring automatic kernel cleanup if the
  controlling userspace agent crashes or exits unexpectedly.

- File Preservation
  A handler-based framework allows specific file types (demonstrated
  here with memfd) to be preserved. Handlers manage the serialization,
  restoration, and lifecycle of their specific file types.

- File-Lifecycle-Bound State
  A new mechanism for managing shared global state whose lifecycle is
  tied to the preservation of one or more files. This is crucial for
  subsystems like IOMMU or HugeTLB, where multiple file descriptors may
  depend on a single, shared underlying resource that must be preserved
  only once.

- KHO Integration
  LUO drives the Kexec Handover framework programmatically to pass its
  serialized metadata to the next kernel. The LUO state is finalized and
  added to the kexec image just before the reboot is triggered. In the
  future this step will also be removed once stateless KHO is
  merged [6].

- Userspace Interface
  Control is provided via ioctl commands on /dev/liveupdate for creating
  and retrieving sessions, as well as on session file descriptors for
  managing individual files.

- Testing
  The series includes a set of selftests, including userspace API
  validation, kexec-based lifecycle tests for various session and file
  scenarios, and a new in-kernel test module to validate the FLB logic.




Introduce LUO, a mechanism intended to facilitate kernel updates while
keeping designated devices operational across the transition (e.g., via
kexec).  The primary use case is updating hypervisors with minimal
disruption to running virtual machines.  For userspace side of hypervisor
update we have copyless migration.  LUO is for updating the kernel.

This initial patch lays the groundwork for the LUO subsystem.

Further functionality, including the implementation of state transition
logic, integration with KHO, and hooks for subsystems and file
descriptors, will be added in subsequent patches.

Create a character device at /dev/liveupdate.

A new uAPI header, <uapi/linux/liveupdate.h>, will define the necessary
structures.  The magic number for IOCTL is registered in
Documentation/userspace-api/ioctl/ioctl-number.rst.

Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Link: https://lore.kernel.org/all/[email protected]/ [1]
Link: https://lore.kernel.org/linux-iommu/[email protected] [2]
Link: https://lore.kernel.org/linux-pci/[email protected] [3]
Link: https://github.com/googleprodkernel/linux-liveupdate/tree/luo/v8 [4]
Link: https://tinyurl.com/luoddesign [5]
Link: https://lore.kernel.org/all/[email protected] [6]
Link: https://lore.kernel.org/all/[email protected] [7]
Link: https://github.com/soleen/linux/blob/luo/v8b03/diff.v7.v8 [8]
Signed-off-by: Pasha Tatashin <[email protected]>
Reviewed-by: Pratyush Yadav <[email protected]>
Reviewed-by: Mike Rapoport (Microsoft) <[email protected]>
Tested-by: David Matlack <[email protected]>
Cc: Aleksander Lobakin <[email protected]>
Cc: Alexander Graf <[email protected]>
Cc: Alice Ryhl <[email protected]>
Cc: Andriy Shevchenko <[email protected]>
Cc: anish kumar <[email protected]>
Cc: Anna Schumaker <[email protected]>
Cc: Bartosz Golaszewski <[email protected]>
Cc: Bjorn Helgaas <[email protected]>
Cc: Borislav Betkov <[email protected]>
Cc: Chanwoo Choi <[email protected]>
Cc: Chen Ridong <[email protected]>
Cc: Chris Li <[email protected]>
Cc: Christian Brauner <[email protected]>
Cc: Daniel Wagner <[email protected]>
Cc: Danilo Krummrich <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: David Jeffery <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Guixin Liu <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Ilpo Järvinen <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Ira Weiny <[email protected]>
Cc: Jann Horn <[email protected]>
Cc: Jason Gunthorpe <[email protected]>
Cc: Jens Axboe <[email protected]>
Cc: Joanthan Cameron <[email protected]>
Cc: Joel Granados <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Lennart Poettering <[email protected]>
Cc: Leon Romanovsky <[email protected]>
Cc: Leon Romanovsky <[email protected]>
Cc: Lukas Wunner <[email protected]>
Cc: Marc Rutland <[email protected]>
Cc: Masahiro Yamada <[email protected]>
Cc: Matthew Maurer <[email protected]>
Cc: Miguel Ojeda <[email protected]>
Cc: Myugnjoo Ham <[email protected]>
Cc: Parav Pandit <[email protected]>
Cc: Randy Dunlap <[email protected]>
Cc: Roman Gushchin <[email protected]>
Cc: Saeed Mahameed <[email protected]>
Cc: Samiullah Khawaja <[email protected]>
Cc: Song Liu <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: Stuart Hayes <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Thomas Gleinxer <[email protected]>
Cc: Thomas Weißschuh <[email protected]>
Cc: Vincent Guittot <[email protected]>
Cc: William Tu <[email protected]>
Cc: Yoann Congal <[email protected]>
Cc: Zijun Hu <[email protected]>
Cc: Pratyush Yadav <[email protected]>
Cc: Zhu Yanjun <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
 2025-11-27 14:24:37 -08:00
Pasha Tatashin 48a1b2321d liveupdate: kho: move to kernel/liveupdate 
Move KHO to kernel/liveupdate/ in preparation of placing all Live Update
core kernel related files to the same place.

[[email protected]: disable the menu when DEFERRED_STRUCT_PAGE_INIT]
  Link: https://lkml.kernel.org/r/CA+CK2bAvh9Oa2SLfsbJ8zztpEjrgr_hr-uGgF1coy8yoibT39A@mail.gmail.com
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Pasha Tatashin <[email protected]>
Reviewed-by: Jason Gunthorpe <[email protected]>
Reviewed-by: Mike Rapoport (Microsoft) <[email protected]>
Cc: Alexander Graf <[email protected]>
Cc: Changyuan Lyu <[email protected]>
Cc: Christian Brauner <[email protected]>
Cc: Jason Gunthorpe <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Masahiro Yamada <[email protected]>
Cc: Miguel Ojeda <[email protected]>
Cc: Pratyush Yadav <[email protected]>
Cc: Randy Dunlap <[email protected]>
Cc: Simon Horman <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Zhu Yanjun <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
 2025-11-27 14:24:33 -08:00