linux-kernel - [PATCH 1/1] mm/memory: Fix boundary check for next PFN in folio_pte

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Message-Id: <20240227070418.62292-1-ioworker0@gmail.com>
Date: Tue, 27 Feb 2024 15:04:18 +0800
From: Lance Yang <ioworker0@...il.com>
To: akpm@...ux-foundation.org
Cc: ryan.roberts@....com,
	21cnbao@...il.com,
	david@...hat.com,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Lance Yang <ioworker0@...il.com>
Subject: [PATCH 1/1] mm/memory: Fix boundary check for next PFN in folio_pte_batch()

Previously, in folio_pte_batch(), only the upper boundary of the
folio was checked using '>=' for comparison. This led to
incorrect behavior when the next PFN exceeded the lower boundary
of the folio, especially in corner cases where the next PFN might
fall into a different folio.

Signed-off-by: Lance Yang <ioworker0@...il.com>
---
 mm/memory.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 642b4f2be523..e5291d1e8c37 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -986,12 +986,15 @@ static inline int folio_pte_batch(struct folio *folio, unsigned long addr,
 		pte_t *start_ptep, pte_t pte, int max_nr, fpb_t flags,
 		bool *any_writable)
 {
-	unsigned long folio_end_pfn = folio_pfn(folio) + folio_nr_pages(folio);
+	unsigned long folio_start_pfn, folio_end_pfn;
 	const pte_t *end_ptep = start_ptep + max_nr;
 	pte_t expected_pte, *ptep;
 	bool writable;
 	int nr;
 
+	folio_start_pfn = folio_pfn(folio);
+	folio_end_pfn = folio_start_pfn + folio_nr_pages(folio);
+
 	if (any_writable)
 		*any_writable = false;
 
@@ -1015,7 +1018,7 @@ static inline int folio_pte_batch(struct folio *folio, unsigned long addr,
 		 * corner cases the next PFN might fall into a different
 		 * folio.
 		 */
-		if (pte_pfn(pte) >= folio_end_pfn)
+		if (pte_pfn(pte) >= folio_end_pfn || pte_pfn(pte) < folio_start_pfn)
 			break;
 
 		if (any_writable)
-- 
2.33.1