linux-kernel - [PATCH 2/4] mm: page_table_check: use new iteration API

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Message-ID: <85f11743d259d5e4a1f47456fbcda82ff6db9ab3.1739931468.git.luizcap@redhat.com>
Date: Tue, 18 Feb 2025 21:17:48 -0500
From: Luiz Capitulino <luizcap@...hat.com>
To: linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	david@...hat.com,
	yuzhao@...gle.com,
	pasha.tatashin@...een.com
Cc: akpm@...ux-foundation.org,
	hannes@...xchg.org,
	muchun.song@...ux.dev,
	luizcap@...hat.com
Subject: [PATCH 2/4] mm: page_table_check: use new iteration API

The page_ext_next() function assumes that page extension objects for a
page order allocation always reside in the same memory section, which
may not be true and could lead to crashes. Use the new page_ext
iteration API instead.

Fixes: cf54f310d0d3 ("mm/hugetlb: use __GFP_COMP for gigantic folios")
Signed-off-by: Luiz Capitulino <luizcap@...hat.com>
---
 mm/page_table_check.c | 39 ++++++++++++---------------------------
 1 file changed, 12 insertions(+), 27 deletions(-)

diff --git a/mm/page_table_check.c b/mm/page_table_check.c
index 509c6ef8de400..b52e04d31c809 100644
--- a/mm/page_table_check.c
+++ b/mm/page_table_check.c
@@ -62,24 +62,20 @@ static struct page_table_check *get_page_table_check(struct page_ext *page_ext)
  */
 static void page_table_check_clear(unsigned long pfn, unsigned long pgcnt)
 {
+	struct page_ext_iter iter;
 	struct page_ext *page_ext;
 	struct page *page;
-	unsigned long i;
 	bool anon;
 
 	if (!pfn_valid(pfn))
 		return;
 
 	page = pfn_to_page(pfn);
-	page_ext = page_ext_get(page);
-
-	if (!page_ext)
-		return;
-
 	BUG_ON(PageSlab(page));
 	anon = PageAnon(page);
 
-	for (i = 0; i < pgcnt; i++) {
+	rcu_read_lock();
+	for_each_page_ext(page, pgcnt, page_ext, iter) {
 		struct page_table_check *ptc = get_page_table_check(page_ext);
 
 		if (anon) {
@@ -89,9 +85,8 @@ static void page_table_check_clear(unsigned long pfn, unsigned long pgcnt)
 			BUG_ON(atomic_read(&ptc->anon_map_count));
 			BUG_ON(atomic_dec_return(&ptc->file_map_count) < 0);
 		}
-		page_ext = page_ext_next(page_ext);
 	}
-	page_ext_put(page_ext);
+	rcu_read_unlock();
 }
 
 /*
@@ -102,24 +97,20 @@ static void page_table_check_clear(unsigned long pfn, unsigned long pgcnt)
 static void page_table_check_set(unsigned long pfn, unsigned long pgcnt,
 				 bool rw)
 {
+	struct page_ext_iter iter;
 	struct page_ext *page_ext;
 	struct page *page;
-	unsigned long i;
 	bool anon;
 
 	if (!pfn_valid(pfn))
 		return;
 
 	page = pfn_to_page(pfn);
-	page_ext = page_ext_get(page);
-
-	if (!page_ext)
-		return;
-
 	BUG_ON(PageSlab(page));
 	anon = PageAnon(page);
 
-	for (i = 0; i < pgcnt; i++) {
+	rcu_read_lock();
+	for_each_page_ext(page, pgcnt, page_ext, iter) {
 		struct page_table_check *ptc = get_page_table_check(page_ext);
 
 		if (anon) {
@@ -129,9 +120,8 @@ static void page_table_check_set(unsigned long pfn, unsigned long pgcnt,
 			BUG_ON(atomic_read(&ptc->anon_map_count));
 			BUG_ON(atomic_inc_return(&ptc->file_map_count) < 0);
 		}
-		page_ext = page_ext_next(page_ext);
 	}
-	page_ext_put(page_ext);
+	rcu_read_unlock();
 }
 
 /*
@@ -140,24 +130,19 @@ static void page_table_check_set(unsigned long pfn, unsigned long pgcnt,
  */
 void __page_table_check_zero(struct page *page, unsigned int order)
 {
+	struct page_ext_iter iter;
 	struct page_ext *page_ext;
-	unsigned long i;
 
 	BUG_ON(PageSlab(page));
 
-	page_ext = page_ext_get(page);
-
-	if (!page_ext)
-		return;
-
-	for (i = 0; i < (1ul << order); i++) {
+	rcu_read_lock();
+	for_each_page_ext_order(page, order, page_ext, iter) {
 		struct page_table_check *ptc = get_page_table_check(page_ext);
 
 		BUG_ON(atomic_read(&ptc->anon_map_count));
 		BUG_ON(atomic_read(&ptc->file_map_count));
-		page_ext = page_ext_next(page_ext);
 	}
-	page_ext_put(page_ext);
+	rcu_read_unlock();
 }
 
 void __page_table_check_pte_clear(struct mm_struct *mm, pte_t pte)
-- 
2.48.1