Merge tag 'mm-stable-2023-05-03-16-22' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Pull more MM updates from Andrew Morton:

 - Some DAMON cleanups from Kefeng Wang

 - Some KSM work from David Hildenbrand, to make the PR_SET_MEMORY_MERGE
   ioctl's behavior more similar to KSM's behavior.

[ Andrew called these "final", but I suspect we'll have a series fixing
  up the fact that the last commit in the dmapools series in the
  previous pull seems to have unintentionally just reverted all the
  other commits in the same series..   - Linus ]

* tag 'mm-stable-2023-05-03-16-22' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm:
  mm: hwpoison: coredump: support recovery from dump_user_range()
  mm/page_alloc: add some comments to explain the possible hole in __pageblock_pfn_to_page()
  mm/ksm: move disabling KSM from s390/gmap code to KSM code
  selftests/ksm: ksm_functional_tests: add prctl unmerge test
  mm/ksm: unmerge and clear VM_MERGEABLE when setting PR_SET_MEMORY_MERGE=0
  mm/damon/paddr: fix missing folio_sz update in damon_pa_young()
  mm/damon/paddr: minor refactor of damon_pa_mark_accessed_or_deactivate()
  mm/damon/paddr: minor refactor of damon_pa_pageout()

1 files changed, 9 insertions, 0 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 9de2a18519a1..47421bedc12b 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1502,6 +1502,15 @@ void __free_pages_core(struct page *page, unsigned int order)
  * interleaving within a single pageblock. It is therefore sufficient to check
  * the first and last page of a pageblock and avoid checking each individual
  * page in a pageblock.
+ *
+ * Note: the function may return non-NULL struct page even for a page block
+ * which contains a memory hole (i.e. there is no physical memory for a subset
+ * of the pfn range). For example, if the pageblock order is MAX_ORDER, which
+ * will fall into 2 sub-sections, and the end pfn of the pageblock may be hole
+ * even though the start pfn is online and valid. This should be safe most of
+ * the time because struct pages are still initialized via init_unavailable_range()
+ * and pfn walkers shouldn't touch any physical memory range for which they do
+ * not recognize any specific metadata in struct pages.
  */
 struct page *__pageblock_pfn_to_page(unsigned long start_pfn,
 				     unsigned long end_pfn, struct zone *zone)