[PATCH v2 0/5] hibernation: make safe_copy_page more robust and remove debug_pagealloc support

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

When hibernation creates a memory image, it uses set_direct_map() APIs to
temporarily map pages that are marked as not present in the kernel page
tables.

Initially, this was intended to support debug_pagealloc along with
hibernation on x86.

With the increasing desire to use set_direct_map APIs for hardening
features and with their inconsistent implementations across architectures,
using kernel_page_present() + set_direct_map_valid_noflush() to save
non-present pages in the hibernation image is not very safe, to say the
least.

Worse, some combinations of debug features, such as debug_pagealloc and
PAGE_POISON cause a crash during restore.

Keeping debug_pagealloc compatible with hibernation requires a complex
infrastructure for tracking free unmapped pages with a page flag/page type,
verifying that it is actually a free page that hibernate_map_page() tries
to remap and making sure there are no stale or failed page table updates.
With init_on_{alloc,free} and/or PAGE_POISON on top, this also requires the
ability to map and initialize these free pages on restore.

This complexity does not seem justified for a somewhat niche debugging
scenario.

Instead of a complex fix to support hibernation with debug_pagealloc, make
sure that copy_data_pages() and its helpers properly handle errors that may
happen during page table updates, explicitly enable saving of KFENCE pages
and disallow hibernation when debug_pagealloc is enabled.

---
Changes in v2:
- use hibernation_available() to close secretmem race
- rename kfence_restore_mapping() to kfence_reset_mapping() for better
  symmetry with kfence_force_mapping()

- Link to v1: https://patch.msgid.link/20260917-hibernation-v1-0-7f7dfae3dbe0@kernel.org

---
Mike Rapoport (Microsoft) (5):
      hibernation: make swsusp_page helpers static
      hibernation: ensure secretmem pages don't reach a snapshot
      hibernate: handle potential errors in hibernate_{map,unmap}_page()
      hibernation, KFENCE: explicitly map/unmap KFENCE pages
      hibernation: make hibernation unavailable when debug_pagealloc is on

 include/linux/kfence.h   |  29 ++++++++++
 include/linux/suspend.h  |   6 ---
 kernel/power/hibernate.c |   6 +++
 kernel/power/snapshot.c  | 137 +++++++++++++++++++++++++----------------------
 mm/kfence/core.c         |  52 +++++++++++++++++-
 5 files changed, 159 insertions(+), 71 deletions(-)
---
base-commit: 99d08cb94abb5aeefbda36dc8bd15677c6f76f45
change-id: 20260916-hibernation-7603b86eb981

--
Sincerely yours,
Mike.