Commit fa5a0617 authored Oct 22, 2025 by Zi Yan Committed by Andrew Morton Nov 09, 2025

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/ [1]
Link: https://lkml.kernel.org/r/20251023030521.473097-1-ziy@nvidia.com


Fixes: c010d47f ("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>

parent f5548c31

mm/huge_memory.c

+20 −3

Original line number	Diff line number	Diff line
		@@ -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.