Patch series "Make KHO Stateless", v9.
This series transitions KHO from an xarray-based metadata tracking system
with serialization to a radix tree data structure that can be passed
directly to the next kernel.
The key motivations for this change are to:
- Eliminate the need for data serialization before kexec.
- Remove the KHO finalize state.
- Pass preservation metadata more directly to the next kernel via the FDT.
The new approach uses a radix tree to mark preserved pages. A page's
physical address and its order are encoded into a single value. The tree
is composed of multiple levels of page-sized tables, with leaf nodes being
bitmaps where each set bit represents a preserved page. The physical
address of the radix tree's root is passed in the FDT, allowing the next
kernel to reconstruct the preserved memory map.
This series is broken down into the following patches:
1. kho: Adopt radix tree for preserved memory tracking:
Replaces the xarray-based tracker with the new radix tree
implementation and increments the ABI version.
2. kho: Remove finalize state and clients:
Removes the now-obsolete kho_finalize() function and its usage
from client code and debugfs.
This patch (of 2):
Introduce a radix tree implementation for tracking preserved memory pages
and switch the KHO memory tracking mechanism to use it. This lays the
groundwork for a stateless KHO implementation that eliminates the need for
serialization and the associated "finalize" state.
This patch introduces the core radix tree data structures and constants to
the KHO ABI. It adds the radix tree node and leaf structures, along with
documentation for the radix tree key encoding scheme that combines a
page's physical address and order.
To support broader use by other kernel subsystems, such as hugetlb
preservation, the core radix tree manipulation functions are exported as a
public API.
The xarray-based memory tracking is replaced with this new radix tree
implementation. The core KHO preservation and unpreservation functions
are wired up to use the radix tree helpers. On boot, the second kernel
restores the preserved memory map by walking the radix tree whose root
physical address is passed via the FDT.
The ABI `compatible` version is bumped to "kho-v2" to reflect the
structural changes in the preserved memory map and sub-FDT property names.
This includes renaming "fdt" to "preserved-data" to better reflect that
preserved state may use formats other than FDT.
[ran.xiaokai@zte.com.cn: fix child node parsing for debugfs in/sub_fdts]
Link: https://lkml.kernel.org/r/20260309033530.244508-1-ranxiaokai627@163.com
Link: https://lkml.kernel.org/r/20260206021428.3386442-1-jasonmiu@google.com
Link: https://lkml.kernel.org/r/20260206021428.3386442-2-jasonmiu@google.com
Signed-off-by: Jason Miu <jasonmiu@google.com>
Signed-off-by: Ran Xiaokai <ran.xiaokai@zte.com.cn>
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>
The `struct kho_vmalloc` defines the in-memory layout for preserving
vmalloc regions across kexec. This layout is a contract between kernels
and part of the KHO ABI.
To reflect this relationship, the related structs and helper macros are
relocated to the ABI header, `include/linux/kho/abi/kexec_handover.h`.
This move places the structure's definition under the protection of the
KHO_FDT_COMPATIBLE version string.
The structure and its components are now also documented within the ABI
header to describe the contract and prevent ABI breaks.
[rppt@kernel.org: update comment, per Pratyush]
Link: https://lkml.kernel.org/r/aW_Mqp6HcqLwQImS@kernel.org
Link: https://lkml.kernel.org/r/20260105165839.285270-6-rppt@kernel.org
Signed-off-by: Jason Miu <jasonmiu@google.com>
Co-developed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Alexander Graf <graf@amazon.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Pratyush Yadav <pratyush@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Introduce the `include/linux/kho/abi/kexec_handover.h` header file, which
defines the stable ABI for the KHO mechanism. This header specifies how
preserved data is passed between kernels using an FDT.
The ABI contract includes the FDT structure, node properties, and the
"kho-v1" compatible string. By centralizing these definitions, this
header serves as the foundational agreement for inter-kernel communication
of preserved states, ensuring forward compatibility and preventing
misinterpretation of data across kexec transitions.
Since the ABI definitions are now centralized in the header files, the
YAML files that previously described the FDT interfaces are redundant.
These redundant files have therefore been removed.
Link: https://lkml.kernel.org/r/20260105165839.285270-5-rppt@kernel.org
Signed-off-by: Jason Miu <jasonmiu@google.com>
Co-developed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: Pratyush Yadav <pratyush@kernel.org>
Cc: Alexander Graf <graf@amazon.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
