gentle ping
On Thu, Sep 17, 2026 at 09:07:02AM +0300, Mike Rapoport (Microsoft) wrote:
> 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.
>
> ---
> 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: 0820e2e85e8aafde66256c567ad37a5b15708d4d
> change-id: 20260916-hibernation-7603b86eb981
>
> --
> Sincerely yours,
> Mike.
>
--
Sincerely yours,
Mike.