linux.git/kernel/liveupdate/luo_core.c, branch v7.2-rc2

liveupdate: defer session block allocation and physical address setting

2026-06-03T18:15:46+00:00

Currently, luo_session_setup_outgoing() allocates the session block and
sets its physical address in the header immediately. With upcoming
dynamic block-based session management, this makes the first block
different from the rest. Move the allocation to where it is first needed.

Acked-by: Mike Rapoport (Microsoft) 
Reviewed-by: Pratyush Yadav (Google) 
Signed-off-by: Pasha Tatashin 
Link: https://patch.msgid.link/20260603154402.468928-9-pasha.tatashin@soleen.com
Signed-off-by: Mike Rapoport (Microsoft)

liveupdate: register luo_ser as KHO subtree

2026-06-03T18:15:45+00:00

Entirely remove the LUO FDT wrapper since the FDT only carries the
compatible string and the pointer to the centralized struct luo_ser.
Instead, register the struct luo_ser via the KHO raw subtree
API, placing the compatibility string inside the structure itself.

Acked-by: Mike Rapoport (Microsoft) 
Reviewed-by: Pratyush Yadav (Google) 
Signed-off-by: Pasha Tatashin 
Link: https://patch.msgid.link/20260603154402.468928-5-pasha.tatashin@soleen.com
Signed-off-by: Mike Rapoport (Microsoft)

liveupdate: centralize state management into struct luo_ser

2026-06-03T18:15:45+00:00

Transition the LUO to ABI v2, which centralizes state management into a
single struct luo_ser header.

Previously, LUO state was spread across multiple FDT properties and
subnodes. ABI v2 simplifies this by placing all core state, including
the liveupdate number and physical addresses for sessions and FLB
headers into a centralized struct luo_ser.

Note that this change introduces a semantic difference: the sessions
and FLB serialization formats are no longer completely independent of
the core LUO. Their metadata (such as physical addresses for sessions
and FLB headers) is now coupled to and managed via the centralized
struct luo_ser.

Reviewed-by: Pratyush Yadav (Google) 
Acked-by: Mike Rapoport (Microsoft) 
Signed-off-by: Pasha Tatashin 
Link: https://patch.msgid.link/20260603154402.468928-4-pasha.tatashin@soleen.com
Signed-off-by: Mike Rapoport (Microsoft)

liveupdate: document liveupdate=on

2026-06-01T06:19:38+00:00

While the liveupdate= parameter is documented in kernel-parameters.txt,
it is not listed in LUO's user facing documentation. This can make it
hard for users to figure out how to enable the subsystem, since enabling
just the config isn't enough.

Note the need for the kernel parameter in LUO core documentation, which
gets exported to Documentation/core-api/liveupdate.rst.

Suggested-by: Luca Boccassi 
Signed-off-by: Pratyush Yadav (Google) 
Acked-by: Luca Boccassi 
Link: https://patch.msgid.link/20260519125714.2435640-1-pratyush@kernel.org
Signed-off-by: Pasha Tatashin 
Signed-off-by: Mike Rapoport (Microsoft)

liveupdate: protect file handler list with rwsem

2026-04-18T07:10:49+00:00

Because liveupdate file handlers will no longer hold a module reference
when registered, we must ensure that the access to the handler list is
protected against concurrent module unloading.

Utilize the global luo_register_rwlock to protect the global registry of
file handlers.  Read locks are taken during list traversals in
luo_preserve_file() and luo_file_deserialize().  Write locks are taken
during registration and unregistration.

Link: https://lore.kernel.org/20260327033335.696621-4-pasha.tatashin@soleen.com
Signed-off-by: Pasha Tatashin 
Reviewed-by: Pratyush Yadav (Google) 
Cc: David Matlack 
Cc: Mike Rapoport 
Cc: Samiullah Khawaja 
Signed-off-by: Andrew Morton

kho: persist blob size in KHO FDT

2026-04-18T07:10:48+00:00

kho_add_subtree() accepts a size parameter but only forwards it to
debugfs.  The size is not persisted in the KHO FDT, so it is lost across
kexec.  This makes it impossible for the incoming kernel to determine the
blob size without understanding the blob format.

Store the blob size as a "blob-size" property in the KHO FDT alongside the
"preserved-data" physical address.  This allows the receiving kernel to
recover the size for any blob regardless of format.

Also extend kho_retrieve_subtree() with an optional size output parameter
so callers can learn the blob size without needing to understand the blob
format.  Update all callers to pass NULL for the new parameter.

Link: https://lore.kernel.org/20260316-kho-v9-3-ed6dcd951988@debian.org
Signed-off-by: Breno Leitao 
Reviewed-by: Mike Rapoport (Microsoft) 
Reviewed-by: Pratyush Yadav 
Cc: Alexander Graf 
Cc: David Hildenbrand 
Cc: Jonathan Corbet 
Cc: "Liam R. Howlett" 
Cc: Lorenzo Stoakes 
Cc: Michal Hocko 
Cc: Pasha Tatashin 
Cc: SeongJae Park 
Cc: Shuah Khan 
Cc: Suren Baghdasaryan 
Cc: Vlastimil Babka 
Signed-off-by: Andrew Morton

kho: add size parameter to kho_add_subtree()

2026-04-18T07:10:48+00:00

Patch series "kho: history: track previous kernel version and kexec boot
count", v9.

Use Kexec Handover (KHO) to pass the previous kernel's version string and
the number of kexec reboots since the last cold boot to the next kernel,
and print it at boot time.

Example
=======
	[    0.000000] Linux version 6.19.0-rc3-upstream-00047-ge5d992347849
	...
	[    0.000000] KHO: exec from: 6.19.0-rc4-next-20260107upstream-00004-g3071b0dc4498 (count 1)

Motivation
==========

Bugs that only reproduce when kexecing from specific kernel versions are
difficult to diagnose.  These issues occur when a buggy kernel kexecs into
a new kernel, with the bug manifesting only in the second kernel.

Recent examples include:

 * eb2266312507 ("x86/boot: Fix page table access in 5-level to 4-level paging transition")
 * 77d48d39e991 ("efistub/tpm: Use ACPI reclaim memory for event log to avoid corruption")
 * 64b45dd46e15 ("x86/efi: skip memattr table on kexec boot")

As kexec-based reboots become more common, these version-dependent bugs
are appearing more frequently.  At scale, correlating crashes to the
previous kernel version is challenging, especially when issues only occur
in specific transition scenarios.

Some bugs manifest only after multiple consecutive kexec reboots. 
Tracking the kexec count helps identify these cases (this metric is
already used by live update sub-system).

KHO provides a reliable mechanism to pass information between kernels.  By
carrying the previous kernel's release string and kexec count forward, we
can print this context at boot time to aid debugging.

The goal of this feature is to have this information being printed in
early boot, so, users can trace back kernel releases in kexec.  Systemd is
not helpful because we cannot assume that the previous kernel has systemd
or even write access to the disk (common when using Linux as bootloaders)


This patch (of 6):

kho_add_subtree() assumes the fdt argument is always an FDT and calls
fdt_totalsize() on it in the debugfs code path.  This assumption will
break if a caller passes arbitrary data instead of an FDT.

When CONFIG_KEXEC_HANDOVER_DEBUGFS is enabled, kho_debugfs_fdt_add() calls
__kho_debugfs_fdt_add(), which executes:

    f->wrapper.size = fdt_totalsize(fdt);

Fix this by adding an explicit size parameter to kho_add_subtree() so
callers specify the blob size.  This allows subtrees to contain arbitrary
data formats, not just FDTs.  Update all callers:

  - memblock.c: use fdt_totalsize(fdt)
  - luo_core.c: use fdt_totalsize(fdt_out)
  - test_kho.c: use fdt_totalsize()
  - kexec_handover.c (root fdt): use fdt_totalsize(kho_out.fdt)

Also update __kho_debugfs_fdt_add() to receive the size explicitly instead
of computing it internally via fdt_totalsize().  In kho_in_debugfs_init(),
pass fdt_totalsize() for the root FDT and sub-blobs since all current
users are FDTs.  A subsequent patch will persist the size in the KHO FDT
so the incoming side can handle non-FDT blobs correctly.

Link: https://lore.kernel.org/20260323110747.193569-1-duanchenghao@kylinos.cn
Link: https://lore.kernel.org/20260316-kho-v9-1-ed6dcd951988@debian.org
Signed-off-by: Breno Leitao 
Suggested-by: Pratyush Yadav 
Reviewed-by: Mike Rapoport (Microsoft) 
Reviewed-by: Pratyush Yadav 
Cc: Alexander Graf 
Cc: David Hildenbrand 
Cc: Jonathan Corbet 
Cc: "Liam R. Howlett" 
Cc: Lorenzo Stoakes 
Cc: Michal Hocko 
Cc: Pasha Tatashin 
Cc: SeongJae Park 
Cc: Shuah Khan 
Cc: Suren Baghdasaryan 
Cc: Vlastimil Babka 
Signed-off-by: Andrew Morton

kho: remove finalize state and clients

2026-04-05T20:53:04+00:00

Eliminate the `kho_finalize()` function and its associated state from the
KHO subsystem.  The transition to a radix tree for memory tracking makes
the explicit "finalize" state and its serialization step obsolete.

Remove the `kho_finalize()` and `kho_finalized()` APIs and their stub
implementations.  Update KHO client code and the debugfs interface to no
longer call or depend on the `kho_finalize()` mechanism.

Complete the move towards a stateless KHO, simplifying the overall design
by removing unnecessary state management.

Link: https://lkml.kernel.org/r/20260206021428.3386442-3-jasonmiu@google.com
Signed-off-by: Jason Miu 
Reviewed-by: Pasha Tatashin 
Reviewed-by: Mike Rapoport (Microsoft) 
Cc: Alexander Graf 
Cc: Baoquan He 
Cc: Changyuan Lyu 
Cc: David Matlack 
Cc: David Rientjes 
Cc: Jason Gunthorpe 
Cc: Pratyush Yadav 
Cc: Ran Xiaokai 
Signed-off-by: Andrew Morton

liveupdate: luo_flb: introduce File-Lifecycle-Bound global state

2026-02-08T08:13:33+00:00

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/20251218155752.3045808-5-pasha.tatashin@soleen.com
Signed-off-by: Pasha Tatashin 
Cc: Alexander Graf 
Cc: David Gow 
Cc: David Matlack 
Cc: David Rientjes 
Cc: Jonathan Corbet 
Cc: Kees Cook 
Cc: Mike Rapoport 
Cc: Petr Mladek 
Cc: Pratyush Yadav 
Cc: Samiullah Khawaja 
Cc: Tamir Duberstein 
Signed-off-by: Andrew Morton

kho: docs: combine concepts and FDT documentation

2026-01-27T03:07:11+00:00

Currently index.rst in KHO documentation looks empty and sad as it only
contains links to "Kexec Handover Concepts" and "KHO FDT" chapters.

Inline contents of these chapters into index.rst to provide a single
coherent chapter describing KHO.

While on it, drop parts of the KHO FDT description that will be superseded
by addition of KHO ABI documentation.

[rppt@kernel.org: fix Documentation/core-api/kho/index.rst]
  Link: https://lkml.kernel.org/r/aV4bnHlBXGpT_FMc@kernel.org
Link: https://lkml.kernel.org/r/20260105165839.285270-4-rppt@kernel.org
Signed-off-by: Mike Rapoport (Microsoft) 
Reviewed-by: Pratyush Yadav 
Cc: Alexander Graf 
Cc: Jason Miu 
Cc: Jonathan Corbet 
Cc: Pratyush Yadav 
Signed-off-by: Andrew Morton