mm/huge_memory: preserve PG_has_hwpoisoned if a folio is split to >0 order

folio split clears PG_has_hwpoisoned, but the flag should be preserved in
after-split folios containing pages with PG_hwpoisoned flag if the folio
is split to >0 order folios.  Scan all pages in a to-be-split folio to
determine which after-split folios need the flag.

An alternatives is to change PG_has_hwpoisoned to PG_maybe_hwpoisoned to
avoid the scan and set it on all after-split folios, but resulting false
positive has undesirable negative impact.  To remove false positive,
caller of folio_test_has_hwpoisoned() and folio_contain_hwpoisoned_page()
needs to do the scan.  That might be causing a hassle for current and
future callers and more costly than doing the scan in the split code.
More details are discussed in [1].

This issue can be exposed via:
1. splitting a has_hwpoisoned folio to >0 order from debugfs interface;
2. truncating part of a has_hwpoisoned folio in
   truncate_inode_partial_folio().

And later accesses to a hwpoisoned page could be possible due to the
missing has_hwpoisoned folio flag.  This will lead to MCE errors.

Link: https://lore.kernel.org/all/CAHbLzkoOZm0PXxE9qwtF4gKR=cpRXrSrJ9V9Pm2DJexs985q4g@mail.gmail.com/
Link: https://lkml.kernel.org/r/20251023030521.473097-1-ziy@nvidia.com
Fixes: c010d47f107f ("mm: thp: split huge page to any lower order pages")
Signed-off-by: Zi Yan <ziy@nvidia.com>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Yang Shi <yang@os.amperecomputing.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Lance Yang <lance.yang@linux.dev>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Wei Yang <richard.weiyang@gmail.com>
Cc: Pankaj Raghav <kernel@pankajraghav.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Jane Chu <jane.chu@oracle.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Luis Chamberalin <mcgrof@kernel.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Naoya Horiguchi <nao.horiguchi@gmail.com>
Cc: Nico Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index feac4aef7dfbdb9e51bbd2be13dce81167bf1995..b4ff49d9650138ec37e94a9d24412e571747bef4 100644 (file)
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3263,6 +3263,14 @@ bool can_split_folio(struct folio *folio, int caller_pins, int *pextra_pins)
                                        caller_pins;
 }
 
+static bool page_range_has_hwpoisoned(struct page *page, long nr_pages)
+{
+       for (; nr_pages; page++, nr_pages--)
+               if (PageHWPoison(page))
+                       return true;
+       return false;
+}
+
 /*
  * It splits @folio into @new_order folios and copies the @folio metadata to
  * all the resulting folios.
@@ -3270,17 +3278,24 @@ bool can_split_folio(struct folio *folio, int caller_pins, int *pextra_pins)
 static void __split_folio_to_order(struct folio *folio, int old_order,
                int new_order)
 {
+       /* Scan poisoned pages when split a poisoned folio to large folios */
+       const bool handle_hwpoison = folio_test_has_hwpoisoned(folio) && new_order;
        long new_nr_pages = 1 << new_order;
        long nr_pages = 1 << old_order;
        long i;
 
+       folio_clear_has_hwpoisoned(folio);
+
+       /* Check first new_nr_pages since the loop below skips them */
+       if (handle_hwpoison &&
+           page_range_has_hwpoisoned(folio_page(folio, 0), new_nr_pages))
+               folio_set_has_hwpoisoned(folio);
        /*
         * Skip the first new_nr_pages, since the new folio from them have all
         * the flags from the original folio.
         */
        for (i = new_nr_pages; i < nr_pages; i += new_nr_pages) {
                struct page *new_head = &folio->page + i;
-
                /*
                 * Careful: new_folio is not a "real" folio before we cleared PageTail.
                 * Don't pass it around before clear_compound_head().
@@ -3322,6 +3337,10 @@ static void __split_folio_to_order(struct folio *folio, int old_order,
                                 (1L << PG_dirty) |
                                 LRU_GEN_MASK | LRU_REFS_MASK));
 
+               if (handle_hwpoison &&
+                   page_range_has_hwpoisoned(new_head, new_nr_pages))
+                       folio_set_has_hwpoisoned(new_folio);
+
                new_folio->mapping = folio->mapping;
                new_folio->index = folio->index + i;
 
@@ -3422,8 +3441,6 @@ static int __split_unmapped_folio(struct folio *folio, int new_order,
        if (folio_test_anon(folio))
                mod_mthp_stat(order, MTHP_STAT_NR_ANON, -1);
 
-       folio_clear_has_hwpoisoned(folio);
-
        /*
         * split to new_order one order at a time. For uniform split,
         * folio is split to new_order directly.