mirror of
https://github.com/torvalds/linux.git
synced 2026-04-18 06:44:00 -04:00
6b0dd42d76
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 <jasonmiu@google.com> Reviewed-by: Pasha Tatashin <pasha.tatashin@soleen.com> Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org> Cc: Alexander Graf <graf@amazon.com> Cc: Baoquan He <bhe@redhat.com> Cc: Changyuan Lyu <changyuanl@google.com> Cc: David Matlack <dmatlack@google.com> Cc: David Rientjes <rientjes@google.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: Pratyush Yadav <pratyush@kernel.org> Cc: Ran Xiaokai <ran.xiaokai@zte.com.cn> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
90 lines
3.3 KiB
ReStructuredText
90 lines
3.3 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0-or-later
|
|
|
|
.. _kho-concepts:
|
|
|
|
========================
|
|
Kexec Handover Subsystem
|
|
========================
|
|
|
|
Overview
|
|
========
|
|
|
|
Kexec HandOver (KHO) is a mechanism that allows Linux to preserve memory
|
|
regions, which could contain serialized system states, across kexec.
|
|
|
|
KHO uses :ref:`flattened device tree (FDT) <kho_fdt>` to pass information about
|
|
the preserved state from pre-exec kernel to post-kexec kernel and :ref:`scratch
|
|
memory regions <kho_scratch>` to ensure integrity of the preserved memory.
|
|
|
|
.. _kho_fdt:
|
|
|
|
KHO FDT
|
|
=======
|
|
Every KHO kexec carries a KHO specific flattened device tree (FDT) blob that
|
|
describes the preserved state. The FDT includes properties describing preserved
|
|
memory regions and nodes that hold subsystem specific state.
|
|
|
|
The preserved memory regions contain either serialized subsystem states, or
|
|
in-memory data that shall not be touched across kexec. After KHO, subsystems
|
|
can retrieve and restore the preserved state from KHO FDT.
|
|
|
|
Subsystems participating in KHO can define their own format for state
|
|
serialization and preservation.
|
|
|
|
KHO FDT and structures defined by the subsystems form an ABI between pre-kexec
|
|
and post-kexec kernels. This ABI is defined by header files in
|
|
``include/linux/kho/abi`` directory.
|
|
|
|
.. toctree::
|
|
:maxdepth: 1
|
|
|
|
abi.rst
|
|
|
|
.. _kho_scratch:
|
|
|
|
Scratch Regions
|
|
===============
|
|
|
|
To boot into kexec, we need to have a physically contiguous memory range that
|
|
contains no handed over memory. Kexec then places the target kernel and initrd
|
|
into that region. The new kernel exclusively uses this region for memory
|
|
allocations before during boot up to the initialization of the page allocator.
|
|
|
|
We guarantee that we always have such regions through the scratch regions: On
|
|
first boot KHO allocates several physically contiguous memory regions. Since
|
|
after kexec these regions will be used by early memory allocations, there is a
|
|
scratch region per NUMA node plus a scratch region to satisfy allocations
|
|
requests that do not require particular NUMA node assignment.
|
|
By default, size of the scratch region is calculated based on amount of memory
|
|
allocated during boot. The ``kho_scratch`` kernel command line option may be
|
|
used to explicitly define size of the scratch regions.
|
|
The scratch regions are declared as CMA when page allocator is initialized so
|
|
that their memory can be used during system lifetime. CMA gives us the
|
|
guarantee that no handover pages land in that region, because handover pages
|
|
must be at a static physical memory location and CMA enforces that only
|
|
movable pages can be located inside.
|
|
|
|
After KHO kexec, we ignore the ``kho_scratch`` kernel command line option and
|
|
instead reuse the exact same region that was originally allocated. This allows
|
|
us to recursively execute any amount of KHO kexecs. Because we used this region
|
|
for boot memory allocations and as target memory for kexec blobs, some parts
|
|
of that memory region may be reserved. These reservations are irrelevant for
|
|
the next KHO, because kexec can overwrite even the original kernel.
|
|
|
|
Kexec Handover Radix Tree
|
|
=========================
|
|
|
|
.. kernel-doc:: include/linux/kho_radix_tree.h
|
|
:doc: Kexec Handover Radix Tree
|
|
|
|
Public API
|
|
==========
|
|
|
|
.. kernel-doc:: kernel/liveupdate/kexec_handover.c
|
|
:export:
|
|
|
|
See Also
|
|
========
|
|
|
|
- :doc:`/admin-guide/mm/kho`
|