From nobody Sun Feb 8 04:11:35 2026 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6083B28EA72 for ; Sat, 20 Dec 2025 20:29:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766262570; cv=none; b=kA3db7A+H3f0NiJ5Zq8EpP0gR6L4mE/raMK0eN3N3imxl4BWJb1bnjXJYUBso4c1fRN9WkcBYRSR6eNSoMAHncBCSlGcGWfENtRbLqkQ+lh6T14fWIaXefi4aZPaiHB3IRXAkByEbqltvgUv3oSaSGSR4grUbTRgFWIvPK16JOI= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766262570; c=relaxed/simple; bh=3djAmIY/bVZRGmdUxEHr+Zlvw5SAngNGjsGgg06NI6I=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=RCFTcFQX5yBNJQIR3hgLnZNd6TW252NlU7qlhCGZsJNZ+BCWSOJ03/IKtDMzReeAmOuvaAndF8C+rCjGFBXXZWm4X42wFaqR7/szwl9G6Q8r7BnSl8Moap+TPZAllfGJxdro7ZIsvugwo2PiGb6EFb4LlMp6d0DOimd9boUutaw= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=KlzGev4g; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="KlzGev4g" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 11CC6C4CEF5; Sat, 20 Dec 2025 20:29:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1766262569; bh=3djAmIY/bVZRGmdUxEHr+Zlvw5SAngNGjsGgg06NI6I=; h=From:To:Cc:Subject:Date:From; b=KlzGev4gP45f+/xC+1UTrC3rgFPVQkqGxSimB3iSE6vnu8awn62WEKEfZtumSrnMJ o/RitvRyR7pqNC8ZPX/VhqbpHv9CzTFypt+oOEwsYC+KeUo1wjt6T68RQBihAVL85k 9WNptPhsVsT+6tuBqfZbtpKIikPccd15iqUXcJFu2eRbtUUigMe4JOYlXGF/VUsIx6 cEyN4jNEzFPOy2F5CZi59YcVRR+bO8M+U4VX2shuigZ5IKOYkCmzyRmjf0IFLs5zB7 ldVlqVpm9cVfK/oamhWyOYHTiWfdby5wIujPQ1vSNCMzs5oyTUBU6HpyRzmtJF7g1X 4AdVlTj0+jF9w== From: Sasha Levin To: akpm@linux-foundation.org, david@kernel.org Cc: xu.xin16@zte.com.cn, chengming.zhou@linux.dev, pedrodemargomes@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Sasha Levin Subject: [PATCH] mm/ksm: fix pte_unmap_unlock of wrong address in break_ksm_pmd_entry Date: Sat, 20 Dec 2025 15:29:26 -0500 Message-ID: <20251220202926.318366-1-sashal@kernel.org> X-Mailer: git-send-email 2.51.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" On ARM32 with HIGHMEM/HIGHPTE, break_ksm_pmd_entry() triggers a BUG during KSM unmerging because pte_unmap_unlock() is passed a pointer that may be beyond the mapped PTE page. The issue occurs when the PTE iteration loop completes without finding a KSM page. After the loop, 'ptep' has been incremented past the last PTE entry. On ARM32 LPAE with 512 PTEs per page (512 * 8 =3D 4096 bytes), this means ptep points to the next page, outside the kmap'd region. When pte_unmap_unlock(ptep, ptl) calls kunmap_local(ptep), it unmaps the wrong page address, leaving the original kmap slot still mapped. The next kmap_local then finds this slot unexpectedly occupied: WARNING: mm/highmem.c:622 kunmap_local_indexed (address mismatch) kernel BUG at mm/highmem.c:564 __kmap_local_pfn_prot (slot not empty) Fix this by passing start_ptep to pte_unmap_unlock(), which always points within the originally mapped PTE page. Reproducer: Run LTP ksm03 test on ARM32 with HIGHMEM enabled. The test triggers KSM merging followed by unmerging (writing 0 then 2 to /sys/kernel/mm/ksm/run), which exercises break_ksm_pmd_entry(). Fixes: 5d4939fc2258 ("ksm: perform a range-walk in break_ksm") Assisted-by: claude-opus-4-5-20251101 Signed-off-by: Sasha Levin Acked-by: David Hildenbrand (Red Hat) Reviewed-by: Chengming Zhou --- mm/ksm.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/ksm.c b/mm/ksm.c index cfc182255c7b..2d89a7c8b4eb 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -650,7 +650,7 @@ static int break_ksm_pmd_entry(pmd_t *pmdp, unsigned lo= ng addr, unsigned long en } } out_unlock: - pte_unmap_unlock(ptep, ptl); + pte_unmap_unlock(start_ptep, ptl); return found; } =20 --=20 2.51.0