[PATCH v9 10/15] mm: Check individual hugetlb pages for poison

So far, is_page_hwpoison() has returned true for the entire poisoned
hugetlb folio, but we can usually allow access to the pages which
aren't poisoned.  It's slightly tricky due to not having a reference
to the folio, but the hugetlb lock can save us here.

Signed-off-by: Matthew Wilcox (Oracle) <[email protected]>
Reviewed-by: Jane Chu <[email protected]>
Reviewed-by: Gregory Price (Meta) <[email protected]>
---
 include/linux/page-flags.h |  4 +++-
 mm/memory-failure.c        | 43 +++++++++++++++++++++++++++++++-------
 2 files changed, 39 insertions(+), 8 deletions(-)

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 7e8784e852fb..5d01e5b28d0f 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -1095,6 +1095,8 @@ static inline bool PageHuge(const struct page *page)
 	return folio_test_hugetlb(page_folio(page));
 }
 
+bool hugetlb_unref_page_hwpoison(const struct page *page);
+
 /*
  * Check if a page is currently marked HWPoisoned.  This check is best
  * effort only and inherently racy: there is no way to synchronize with
@@ -1109,7 +1111,7 @@ static inline bool is_page_hwpoison(const struct page *page)
 		return true;
 	folio = page_folio(page);
 	if (folio_test_huge_poison(folio))
-		return true;
+		return hugetlb_unref_page_hwpoison(page);
 	/* In case we raced with hugetlb transferring flags */
 	return PageHWPoison(page);
 }
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 437a2be6c58c..c0a402522c21 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1820,17 +1820,12 @@ struct hwp_page {
 	struct page *page;
 };
 
-/*
- * Check if a given @page in a hugetlb folio is HWPOISON.
- */
-bool hugetlb_page_hwpoison(const struct folio *folio, const struct page *page)
+static bool precise_page_poisoned(const struct folio *folio,
+		const struct page *page)
 {
 	const struct hwp_page *p;
 	unsigned long flags;
 
-	if (!folio_test_has_hwpoisoned(folio))
-		return false;
-
 	spin_lock_irqsave(&hwp_page_lock, flags);
 
 	/*
@@ -1851,6 +1846,40 @@ bool hugetlb_page_hwpoison(const struct folio *folio, const struct page *page)
 	return p != NULL;
 }
 
+/*
+ * Check if a given @page in a hugetlb folio is HWPOISON.
+ */
+bool hugetlb_page_hwpoison(const struct folio *folio, const struct page *page)
+{
+	if (!folio_test_has_hwpoisoned(folio))
+		return false;
+
+	return precise_page_poisoned(folio, page);
+}
+
+/*
+ * We have no reference on the folio containing this page.
+ * The hugetlb_lock keeps hugetlb folios from being freed.
+ */
+bool hugetlb_unref_page_hwpoison(const struct page *page)
+{
+	const struct folio *folio;
+	unsigned long flags;
+	bool ret;
+
+	spin_lock_irqsave(&hugetlb_lock, flags);
+	folio = page_folio(page);
+	if (!folio_test_huge_poison(folio)) {
+		ret = PageHWPoison(page);
+		goto unlock;
+	}
+
+	ret = precise_page_poisoned(folio, page);
+unlock:
+	spin_unlock_irqrestore(&hugetlb_lock, flags);
+	return ret;
+}
+
 static unsigned long __folio_free_raw_hwp(struct folio *folio, bool move_flag)
 {
 	struct hwp_page *p, *next;
-- 
2.47.3