[PATCH v3 0/5] kho: fix bootmem sizing

["Mike Rapoport (Microsoft)" <rppt@kernel.org>]

There were several reports about issues with KHO bootmem sizing.

The bootmem areas are sized from overlapping views of the memory reserved
in memblock, so on NUMA systems memory allocated on a node is accounted
twice and with CONFIG_NUMA=n the lowmem and the global areas are accounted
once again in the area of node 0. Besides, the lowmem and the global areas
are reserved even when they are empty.

The first patch rejects kho_bootmem=0% that leaves KHO enabled without
usable bootmem.

The second patch makes kexec walk the bootmem areas in address order.
Otherwise kexec on arm64 may fail if a small area at the top of the memory
is the first in the list, and with smaller bootmem areas this becomes more
likely.

The third patch skips empty bootmem areas, the fourth one makes the
lowmem, per-node and global areas cover separate parts of the reserved
memory and the last one updates the documentation.

---
Changes in v3:
- add a patch that rejects kho_bootmem=0%
- set exact_nid in kho_reserve_bootmem_area() only for a valid node
  (Mukesh)
- free bootmem areas in forward order on error
- add braces around multi-line for_each_node_state() body (Pasha)
- add a patch that updates the bootmem documentation (Mukesh)
- Link to v2: https://patch.msgid.link/20261104-kho-bootmem-sizing-v2-0-b0d1a834780f@kernel.org

Changes in v2:
- add a patch that walks bootmem areas in address order
- update kho_bootmem_cnt directly in kho_reserve_bootmem_area() (Pratyush)
- don't reserve the lowmem area if ARCH_LOW_ADDRESS_LIMIT covers all
  memory (Pratyush)
- extend the comment above bootmem_size_update() (Pratyush)
- Link to v1: https://patch.msgid.link/20261103-kho-bootmem-sizing-v1-0-45aa74098f34@kernel.org

---
Mike Rapoport (Microsoft) (5):
      kho: reject zero bootmem scale
      kho: walk bootmem areas in address order
      kho: skip zero-sized lowmem and global bootmem areas
      kho: fix bootmem sizing
      kho: docs: update description of bootmem regions

 Documentation/core-api/kho/index.rst |  31 +++--
 kernel/liveupdate/kexec_handover.c   | 225 +++++++++++++++++++++--------------
 2 files changed, 158 insertions(+), 98 deletions(-)
---
base-commit: 6628e7d4c6b25c8d18f1345e3a20d21829aae7e4
change-id: 20261103-kho-bootmem-sizing-5d6aed47a243

--
Sincerely yours,
Mike.