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d="scan'208";a="91223060" Received: from unknown (HELO gm-smtp10.centrum.cz) ([46.255.225.77]) by antispam64.centrum.cz with ESMTP; 29 Apr 2025 16:22:53 +0200 Received: from localhost.localdomain (ip-213-220-240-96.bb.vodafone.cz [213.220.240.96]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by gm-smtp10.centrum.cz (Postfix) with ESMTPSA id 44AE080911A1; Tue, 29 Apr 2025 16:22:53 +0200 (CEST) From: =?UTF-8?q?Petr=20Van=C4=9Bk?= To: linux-kernel@vger.kernel.org Cc: Andrew Morton , Ryan Roberts , David Hildenbrand , linux-mm@kvack.org, stable@vger.kernel.org, =?UTF-8?q?Petr=20Van=C4=9Bk?= Subject: [PATCH 1/1] mm: Fix folio_pte_batch() overcount with zero PTEs Date: Tue, 29 Apr 2025 16:22:37 +0200 Message-ID: <20250429142237.22138-2-arkamar@atlas.cz> X-Mailer: git-send-email 2.48.1 In-Reply-To: <20250429142237.22138-1-arkamar@atlas.cz> References: <20250429142237.22138-1-arkamar@atlas.cz> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable folio_pte_batch() could overcount the number of contiguous PTEs when pte_advance_pfn() returns a zero-valued PTE and the following PTE in memory also happens to be zero. The loop doesn't break in such a case because pte_same() returns true, and the batch size is advanced by one more than it should be. To fix this, bail out early if a non-present PTE is encountered, preventing the invalid comparison. This issue started to appear after commit 10ebac4f95e7 ("mm/memory: optimize unmap/zap with PTE-mapped THP") and was discovered via git bisect. Fixes: 10ebac4f95e7 ("mm/memory: optimize unmap/zap with PTE-mapped THP") Cc: stable@vger.kernel.org Signed-off-by: Petr Van=C4=9Bk --- mm/internal.h | 2 ++ 1 file changed, 2 insertions(+) diff --git a/mm/internal.h b/mm/internal.h index e9695baa5922..c181fe2bac9d 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -279,6 +279,8 @@ static inline int folio_pte_batch(struct folio *folio, = unsigned long addr, dirty =3D !!pte_dirty(pte); pte =3D __pte_batch_clear_ignored(pte, flags); =20 + if (!pte_present(pte)) + break; if (!pte_same(pte, expected_pte)) break; =20 --=20 2.48.1