On 10/23/2025 4:12 PM, Andrew Morton wrote:
The patch titled Subject: mm/huge_memory: preserve PG_has_hwpoisoned if a folio is split to >0 order has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-huge_memory-preserve-pg_has_hwpoisoned-if-a-folio-is-split-to-0-order.patch
This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...
This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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From: Zi Yan ziy@nvidia.com Subject: mm/huge_memory: preserve PG_has_hwpoisoned if a folio is split to >0 order Date: Wed, 22 Oct 2025 23:05:21 -0400
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:
- splitting a has_hwpoisoned folio to >0 order from debugfs interface;
- 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=cpRXrSrJ9V9Pm2DJexs985... [1] 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 Cc: Pankaj Raghav kernel@pankajraghav.com Reviewed-by: Yang Shi yang@os.amperecomputing.com Cc: Baolin Wang baolin.wang@linux.alibaba.com Cc: Barry Song baohua@kernel.org Cc: Dev Jain dev.jain@arm.com Cc: Jane Chu jane.chu@oracle.com Cc: Lance Yang lance.yang@linux.dev Cc: Liam Howlett liam.howlett@oracle.com Cc: Lorenzo Stoakes lorenzo.stoakes@oracle.com Cc: Luis Chamberalin mcgrof@kernel.org Cc: Matthew Wilcox (Oracle) willy@infradead.org Cc: Miaohe Lin linmiaohe@huawei.com Cc: Naoya Horiguchi nao.horiguchi@gmail.com Cc: Nico Pache npache@redhat.com Cc: Ryan Roberts ryan.roberts@arm.com Cc: Wei Yang richard.weiyang@gmail.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org
mm/huge_memory.c | 23 ++++++++++++++++++++--- 1 file changed, 20 insertions(+), 3 deletions(-)
--- a/mm/huge_memory.c~mm-huge_memory-preserve-pg_has_hwpoisoned-if-a-folio-is-split-to-0-order +++ a/mm/huge_memory.c @@ -3263,6 +3263,14 @@ bool can_split_folio(struct folio *folio 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 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);
Not sure what am I missing, why are we setting hs_hwpoison to the pre-split old folio here? setting it in a new >0 order folio below make sense, setting it back to the big old folio in case of a failed split make sense.
/* * 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(struc (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);
Looks good.
new_folio->mapping = folio->mapping; new_folio->index = folio->index + i;@@ -3422,8 +3441,6 @@ static int __split_unmapped_folio(struct 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.
_
Patches currently in -mm which might be from ziy@nvidia.com are
mm-huge_memory-do-not-change-split_huge_page-target-order-silently.patch mm-huge_memory-preserve-pg_has_hwpoisoned-if-a-folio-is-split-to-0-order.patch
thanks,-jane