6.12-stable review patch. If anyone has any objections, please let me know.
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From: Zi Yan ziy@nvidia.com
commit fa5a061700364bc28ee1cb1095372f8033645dcb upstream.
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=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 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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- mm/huge_memory.c | 25 +++++++++++++++++++++++-- 1 file changed, 23 insertions(+), 2 deletions(-)
--- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -3091,9 +3091,17 @@ static void lru_add_page_tail(struct fol } }
+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; +} + static void __split_huge_page_tail(struct folio *folio, int tail, struct lruvec *lruvec, struct list_head *list, - unsigned int new_order) + unsigned int new_order, const bool handle_hwpoison) { struct page *head = &folio->page; struct page *page_tail = head + tail; @@ -3170,6 +3178,11 @@ static void __split_huge_page_tail(struc folio_set_large_rmappable(new_folio); }
+ /* Set has_hwpoisoned flag on new_folio if any of its pages is HWPoison */ + if (handle_hwpoison && + page_range_has_hwpoisoned(page_tail, 1 << new_order)) + folio_set_has_hwpoisoned(new_folio); + /* Finally unfreeze refcount. Additional reference from page cache. */ page_ref_unfreeze(page_tail, 1 + ((!folio_test_anon(folio) || folio_test_swapcache(folio)) ? @@ -3194,6 +3207,8 @@ static void __split_huge_page(struct pag pgoff_t end, unsigned int new_order) { struct folio *folio = page_folio(page); + /* Scan poisoned pages when split a poisoned folio to large folios */ + const bool handle_hwpoison = folio_test_has_hwpoisoned(folio) && new_order; struct page *head = &folio->page; struct lruvec *lruvec; struct address_space *swap_cache = NULL; @@ -3217,8 +3232,14 @@ static void __split_huge_page(struct pag
ClearPageHasHWPoisoned(head);
+ /* Check first new_nr pages since the loop below skips them */ + if (handle_hwpoison && + page_range_has_hwpoisoned(folio_page(folio, 0), new_nr)) + folio_set_has_hwpoisoned(folio); + for (i = nr - new_nr; i >= new_nr; i -= new_nr) { - __split_huge_page_tail(folio, i, lruvec, list, new_order); + __split_huge_page_tail(folio, i, lruvec, list, new_order, + handle_hwpoison); /* Some pages can be beyond EOF: drop them from page cache */ if (head[i].index >= end) { struct folio *tail = page_folio(head + i);