[PATCH 0/9] kho, liveupdate: KHO/LUO observability

[Chris Down <chris@chrisdown.name>]

At Meta, we are moving towards using live update on hypervisors whose
VMs can't be migrated away first. We also want to preserve service fd
stores across systemctl kexec.

Our kernel rollout is driven by health checks from each host. For
example, an increase in rejected handovers or retrieval failures may be
a reason to stop a rollout, and the bootmem size and sequence number
help us understand what is happening on which hosts. The series exposes:

- how much memory KHO set aside
- whether the new kernel accepted the incoming handover
- whether LUO could give back the state that userspace handed over

We expose these in sysfs so the collector can read them without opening
/dev/liveupdate, which starts deserialisation, or depending on debugfs
or the kernel log.

I also noticed that the incoming kexec metadata page stays reserved
after boot, so free it once its contents have been copied.

Chris Down (9):
  kho: Reclaim the metadata page left reserved after kexec
  kho: Make bootmem reservations visible to fleet monitoring
  liveupdate: Make failed retrieves distinguishable from dropped files
  selftests/liveupdate: Catch incorrect file accounting across kexec
  selftests/kho: Catch missing or zero bootmem reports before kexec
  kho: Expose rejected handovers that look like cold boots
  kho: Report how much handover memory is preserved and restored
  liveupdate: Expose the sequence number for consecutive live updates
  selftests/liveupdate: Check handover revival, sequence and memory
    stats

 .../ABI/testing/sysfs-class-misc-liveupdate   |  56 ++++
 .../ABI/testing/sysfs-kernel-kexec-kdump      |  30 ++
 Documentation/admin-guide/mm/kho.rst          |  19 +-
 Documentation/userspace-api/liveupdate.rst    |   8 +
 MAINTAINERS                                   |   1 +
 include/linux/kexec_handover.h                |   3 +
 kernel/kexec_core.c                           |  26 +-
 kernel/liveupdate/kexec_handover.c            |  82 +++++-
 kernel/liveupdate/luo_core.c                  |  58 ++++
 kernel/liveupdate/luo_file.c                  |  16 +-
 kernel/liveupdate/luo_internal.h              |  34 +++
 kernel/liveupdate/luo_session.c               |   6 +
 tools/testing/selftests/kho/init.c            |  24 ++
 tools/testing/selftests/kho/vmtest.sh         |   1 +
 tools/testing/selftests/liveupdate/Makefile   |   1 +
 tools/testing/selftests/liveupdate/init.c     |   5 +
 .../selftests/liveupdate/luo_handover_stats.c | 258 ++++++++++++++++++
 .../selftests/liveupdate/run-vmtests.sh       |   1 +
 tools/testing/selftests/liveupdate/vmtest.sh  |   2 +
 19 files changed, 624 insertions(+), 7 deletions(-)
 create mode 100644 Documentation/ABI/testing/sysfs-class-misc-liveupdate
 create mode 100644 tools/testing/selftests/liveupdate/luo_handover_stats.c


base-commit: a0dc8eddbfdb6dd9c5c2b70eb66ab49cb1978425
-- 
2.54.0