[PATCH v6 0/2] kexec: keep the next kernel off hardware-poisoned pages

[Breno Leitao]

Memory failures are common enough on large fleets that kexec regularly
lands the next kernel on a frame the memory failure subsystem has already
marked bad. Patch 2 teaches the segment placement to avoid those frames.

Patch 1 is a prerequisite. locate_mem_hole_top_down() walks candidates
downwards without ever checking that the subtraction stays above zero, so
the walk can wrap and report success with a destination outside of RAM.
Patch 2 adds one more downward step to that loop, so the bug is fixed
first and both patches rely on the same bail-out.

Signed-off-by: Breno Leitao <leitao at debian.org>
---
Changes in v6:
- Split the pre-existing top-down underflow out into its own patch, and
  drop the "if (poison < kbuf->memsz)" guard from the hwpoison hunk now
  that the loop bail-out covers it. (Mike Rapoport, Sashiko)
- Reword the changelog: the MCE comes from reading the poison back, not
  from the relocation copy writing it, and the placement paragraphs read
  better split up. (Mike Rapoport)
- Move cond_resched() after the struct page dereference, so the scan does
  not yield between pfn_to_online_page() and is_page_hwpoison().
  (Pratyush Yadav, Sashiko)
- Keep cond_resched() per pfn rather than batching it. (Kiryl Shutsemau,
  Rik van Riel)
- Link to v5: https://patch.msgid.link/20260810-kexec_posioned-v5-1-95e1b5e2e656@debian.org

Changes in v5:
- Return -EHWPOISON instead of -EADDRNOTAVAIL
- Leverage is_page_hwpoison() instead of per-page check
- Link to v4: https://patch.msgid.link/20260807-kexec_posioned-v4-1-70d57f14625d@debian.org

Changes in v4:
- Anchor the top-down hole finder on the first poisoned page in the
  window and the bottom-up one on the last, so each jumps clear of the
  poison in one step. New range_first_hwpoison(). (Kiryl Shutsemau)
- Count a poisoned hugetlb folio in full: the flag lives on the folio,
  not on the subpages, so the per-pfn scan missed poisoned tail pages.
  (Kiryl Shutsemau)
- Link to v3: https://patch.msgid.link/20260803-kexec_posioned-v3-1-83aa6ede0351@debian.org

Changes in v3:
- Return the address of the last poisoned page in the range, or
  PHYS_ADDR_MAX when it is clean, instead of a bool plus an output
  parameter. Renamed to range_last_hwpoison(). (Pratyush Yadav)
- Add cond_resched() to the scan loop, as a segment can span half of
  memory. (Sashiko)
- Link to v2: https://patch.msgid.link/20260730-kexec_posioned-v2-1-f92d18551f64@debian.org

Changes in v2:
- Change from pfn_to_page() to pfn_to_online_page(). (Miaohe Lin)
- Return the poisoned address once we find a hit, to avoid the O(n^2)
  rescan. (Sashiko)
- Link to v1: https://patch.msgid.link/20260728-kexec_posioned-v1-1-160c81d180fe@debian.org

To: Andrew Morton <akpm at linux-foundation.org>
To: David Hildenbrand <david at kernel.org>
To: Lorenzo Stoakes <ljs at kernel.org>
To: "Liam R. Howlett" <liam at infradead.org>
To: Vlastimil Babka <vbabka at kernel.org>
To: Mike Rapoport <rppt at kernel.org>
To: Suren Baghdasaryan <surenb at google.com>
To: Michal Hocko <mhocko at suse.com>
To: Baoquan He <baoquan.he at linux.dev>
To: Pasha Tatashin <pasha.tatashin at soleen.com>
To: Pratyush Yadav <pratyush at kernel.org>
To: Miaohe Lin <linmiaohe at huawei.com>
To: Naoya Horiguchi <nao.horiguchi at gmail.com>
Cc: linux-mm at kvack.org
Cc: linux-kernel at vger.kernel.org
Cc: kexec at lists.infradead.org
Cc: rmikey at meta.com
Cc: riel at surriel.com

---
Breno Leitao (2):
      kexec_file: stop the top-down search before it underflows
      kexec: keep the next kernel off hardware-poisoned pages

 include/linux/mm.h  | 14 ++++++++++++++
 kernel/kexec_core.c | 10 ++++++++++
 kernel/kexec_file.c | 20 +++++++++++++++++++-
 mm/memory-failure.c | 40 ++++++++++++++++++++++++++++++++++++++++
 4 files changed, 83 insertions(+), 1 deletion(-)
---
base-commit: c5e32e86ca02b003f86e095d379b38148999293d
change-id: 20260727-kexec_posioned-72bb0a4143a0

Best regards,
--  
Breno Leitao <leitao at debian.org>