[PATCH v2 2/4] mm/hwpoison: check if a subpage of a hugetlb folio is raw HWPOISON

[Jiaqi Yan <jiaqiyan@google.com>]

Adds the functionality to tell if a subpage of a hugetlb folio is a
raw HWPOISON page. This functionality relies on RawHwpUnreliable to
be not set; otherwise hugepage's HWPOISON list becomes meaningless.

Exports this functionality to be immediately used in the read operation
for hugetlbfs.

Signed-off-by: Jiaqi Yan <jiaqiyan@google.com>
---
 include/linux/hugetlb.h | 19 +++++++++++++++++++
 include/linux/mm.h      |  7 +++++++
 mm/hugetlb.c            | 10 ++++++++++
 mm/memory-failure.c     | 34 ++++++++++++++++++++++++----------
 4 files changed, 60 insertions(+), 10 deletions(-)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 21f942025fec..8b73a12b7b38 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -1013,6 +1013,25 @@ void hugetlb_register_node(struct node *node);
 void hugetlb_unregister_node(struct node *node);
 #endif
 
+/*
+ * Struct raw_hwp_page represents information about "raw error page",
+ * constructing singly linked list from ->_hugetlb_hwpoison field of folio.
+ */
+struct raw_hwp_page {
+	struct llist_node node;
+	struct page *page;
+};
+
+static inline struct llist_head *raw_hwp_list_head(struct folio *folio)
+{
+	return (struct llist_head *)&folio->_hugetlb_hwpoison;
+}
+
+/*
+ * Check if a given raw @subpage in a hugepage @folio is HWPOISON.
+ */
+bool is_raw_hwp_subpage(struct folio *folio, struct page *subpage);
+
 #else	/* CONFIG_HUGETLB_PAGE */
 struct hstate {};
 
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 66032f0d515c..41a283bd41a7 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3671,6 +3671,7 @@ extern const struct attribute_group memory_failure_attr_group;
 extern void memory_failure_queue(unsigned long pfn, int flags);
 extern int __get_huge_page_for_hwpoison(unsigned long pfn, int flags,
 					bool *migratable_cleared);
+extern bool __is_raw_hwp_subpage(struct folio *folio, struct page *subpage);
 void num_poisoned_pages_inc(unsigned long pfn);
 void num_poisoned_pages_sub(unsigned long pfn, long i);
 struct task_struct *task_early_kill(struct task_struct *tsk, int force_early);
@@ -3685,6 +3686,12 @@ static inline int __get_huge_page_for_hwpoison(unsigned long pfn, int flags,
 	return 0;
 }
 
+static inline bool __is_raw_hwp_subpage(struct folio *folio,
+					struct page *subpage)
+{
+	return false;
+}
+
 static inline void num_poisoned_pages_inc(unsigned long pfn)
 {
 }
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index ea24718db4af..6b860de87590 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -7377,6 +7377,16 @@ int get_huge_page_for_hwpoison(unsigned long pfn, int flags,
 	return ret;
 }
 
+bool is_raw_hwp_subpage(struct folio *folio, struct page *subpage)
+{
+	bool ret;
+
+	spin_lock_irq(&hugetlb_lock);
+	ret = __is_raw_hwp_subpage(folio, subpage);
+	spin_unlock_irq(&hugetlb_lock);
+	return ret;
+}
+
 void folio_putback_active_hugetlb(struct folio *folio)
 {
 	spin_lock_irq(&hugetlb_lock);
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index c415c3c462a3..891248e2930e 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1809,18 +1809,32 @@ EXPORT_SYMBOL_GPL(mf_dax_kill_procs);
 #endif /* CONFIG_FS_DAX */
 
 #ifdef CONFIG_HUGETLB_PAGE
-/*
- * Struct raw_hwp_page represents information about "raw error page",
- * constructing singly linked list from ->_hugetlb_hwpoison field of folio.
- */
-struct raw_hwp_page {
-	struct llist_node node;
-	struct page *page;
-};
 
-static inline struct llist_head *raw_hwp_list_head(struct folio *folio)
+bool __is_raw_hwp_subpage(struct folio *folio, struct page *subpage)
 {
-	return (struct llist_head *)&folio->_hugetlb_hwpoison;
+	struct llist_head *raw_hwp_head;
+	struct raw_hwp_page *p, *tmp;
+	bool ret = false;
+
+	if (!folio_test_hwpoison(folio))
+		return false;
+
+	/*
+	 * When RawHwpUnreliable is set, kernel lost track of which subpages
+	 * are HWPOISON. So return as if ALL subpages are HWPOISONed.
+	 */
+	if (folio_test_hugetlb_raw_hwp_unreliable(folio))
+		return true;
+
+	raw_hwp_head = raw_hwp_list_head(folio);
+	llist_for_each_entry_safe(p, tmp, raw_hwp_head->first, node) {
+		if (subpage == p->page) {
+			ret = true;
+			break;
+		}
+	}
+
+	return ret;
 }
 
 static unsigned long __folio_free_raw_hwp(struct folio *folio, bool move_flag)
-- 
2.41.0.162.gfafddb0af9-goog