[PATCH v8 0/2] Make KHO Stateless

Jason Miu
2026-01-30T00:57:56Z

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.

---

Changelog since v7 [1]:
- Initialized anchor_node to NULL in kho_radix_add_page()
- Re-added kho_get_mem_map_phys() and checked the FDT memory address
validity in kho_populate()

[1] https://lore.kernel.org/lkml/20260116034432.1520731-1-jasonmiu@google.com/

---

Jason Miu (2):
kho: Adopt radix tree for preserved memory tracking
kho: Remove finalize state and clients

Documentation/admin-guide/mm/kho.rst | 53 +-
Documentation/core-api/kho/abi.rst | 6 +
Documentation/core-api/kho/index.rst | 18 +-
include/linux/kho/abi/kexec_handover.h | 144 ++++-
include/linux/kho_radix_tree.h | 70 ++
kernel/liveupdate/kexec_handover.c | 674 ++++++++++----------
kernel/liveupdate/kexec_handover_debugfs.c | 23 -
kernel/liveupdate/kexec_handover_internal.h | 3 -
kernel/liveupdate/luo_core.c | 12 +-
tools/testing/selftests/kho/init.c | 20 -
10 files changed, 573 insertions(+), 450 deletions(-)
create mode 100644 include/linux/kho_radix_tree.h

base-commit: 33a647c659ffa5bdb94abc345c8c86768ff96215
--
2.53.0.rc1.225.gd81095ad13-goog