From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 2AD1642DA4A; Mon, 20 Jul 2026 14:41:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784558478; cv=none; b=oVPQ4+mI8HbHautf99NYLxWC17c/vu7WjmSdPOjCWBvcpiV80MxHHiKtNoyd1yi+Ms3J02XIJZJaYNZ4bN4L7z8E21m60AEQ6Y8Ud5Xb8sF/P61Mhu0fytEDScyeBc6lk/+VxFtpbigYSXgXUVYuBDWiHD/MzzKoK8hn6o4jlH8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784558478; c=relaxed/simple; bh=yk0gma+yTZdel+ljE629bRHp848gvZkgeJregd069ZY=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=JSjDKdwGPTh+NU4kuikxlDIvYwDWaCKWS9RA0WzrMgbAjO2FJdwXyM9iklr6rHabmnfn7ehMksYwAzWnWR4A+F2BjvVXE+JIfZ2Oxf4/gTntawTCuL1CQES3NyCGzkMlcpbzhpMbjmIHr7OF77S0M8J6sXNSEUpplyIXeX1DEZI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Xk2CwfJ8; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Xk2CwfJ8" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2D2F51F000E9; Mon, 20 Jul 2026 14:41:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784558476; bh=Q+hgooHeYYaYv/oiqa66MnVBmMzHrm3fz5OuZIxN9Pg=; h=From:Date:Subject:References:In-Reply-To:To:Cc; b=Xk2CwfJ8HL60DsiwzkTy2dmx4IPJaGvy3clwtXHfOLctb/PRF8MP0UeVkjMrXLpqc X4WS2W9ztgR4zmOxglKsN2/48CgCJRBHJz+cSbkn4tO4QjGaKM+hOEcqKQw0wDRnWT 1YUs3hTGnP3EmFHMzbNR4oBE0n2xLUnb6tj8NCpjKgFm16oYCurumYshQqUxynh/4d mbxBldGkcKwB30spX3j5PmyTcJ8UQBYh19Cm1HJ2sVAMTNVNTdn44Lw9deeuDJZv0/ +t5EMQKy+EU8TaYggE9ITM6hRmzQNfyNSb6wj0ah73drSYYTUrn74+PvqOFUFb0kSt yOrY8tOVutBqA== From: "Lorenzo Stoakes (ARM)" Date: Mon, 20 Jul 2026 15:38:41 +0100 Subject: [PATCH v2 15/15] tools/testing/selftests/mm: add MAP_PRIVATE-/dev/zero merge tests 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: 7bit Message-Id: <20260720-b4-scalable-cow-virt-pgoff-v2-15-2d549757a76f@kernel.org> References: <20260720-b4-scalable-cow-virt-pgoff-v2-0-2d549757a76f@kernel.org> In-Reply-To: <20260720-b4-scalable-cow-virt-pgoff-v2-0-2d549757a76f@kernel.org> To: Andrew Morton , David Hildenbrand , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jann Horn , Pedro Falcato , "Matthew Wilcox (Oracle)" , Jan Kara , Miaohe Lin , Naoya Horiguchi , Rik van Riel , Harry Yoo , Lance Yang , Kees Cook , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Usama Arif , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Peter Xu , Xu Xin , Chengming Zhou , Arnd Bergmann , Greg Kroah-Hartman Cc: "Lorenzo Stoakes (ARM)" , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kselftest@vger.kernel.org X-Mailer: b4 0.15.2 X-Developer-Signature: v=1; a=openpgp-sha256; l=4278; i=ljs@kernel.org; h=from:subject:message-id; bh=yk0gma+yTZdel+ljE629bRHp848gvZkgeJregd069ZY=; b=owGbwMvMwCV2fu7ZrsZH9SKMp9WSGLLijN7e2KP42mx2UHD46n83TbO3N4hM99A7xOvx7uKNe Wn5+TtndZSyMIhxMciKKbI8/yK+P0gkbF7nBX83mDmsTCBDGLg4BWAiD00ZGVr436T+lTnYI/ak hVX305pn4i8W28Q1+z2XUYlY3hn3bC/D/wxL/51db5VPmGhsm7yu7Furo/iUVL5MyQXzWlTV0tf u4AcA X-Developer-Key: i=ljs@kernel.org; a=openpgp; fpr=E7F417BF5214569E89D04F46CF9DCD8A81E27F14 Assert that MAP_PRIVATE-mapped /dev/zero mappings behave like they are anonymous. We test both unfaulted and faulted/unfaulted merges - each with the regions having page offset of 0, which would not merge if the mappings were treated as if they were file-backed. With the recent change that makes them behave as pure anonymous mappings, the merges should succeed as their page offsets are equal to their virtual page offsets. Signed-off-by: Lorenzo Stoakes (ARM) --- tools/testing/selftests/mm/merge.c | 104 +++++++++++++++++++++++++++++++++++++ 1 file changed, 104 insertions(+) diff --git a/tools/testing/selftests/mm/merge.c b/tools/testing/selftests/mm/merge.c index c093e27d0aea..edfbd39ae58e 100644 --- a/tools/testing/selftests/mm/merge.c +++ b/tools/testing/selftests/mm/merge.c @@ -1362,6 +1362,110 @@ TEST_F(merge, virt_and_page_offset_mismatch_memfd) ASSERT_EQ(procmap->query.vma_end, (unsigned long)ptr + 5 * page_size); } +TEST_F(merge, merge_map_private_dev_zero_unfaulted) +{ + struct procmap_fd *procmap = &self->procmap; + unsigned int page_size = self->page_size; + char *carveout = self->carveout; + char *ptr, *ptr2; + int fd_zero; + + if (access("/dev/zero", F_OK)) + SKIP(return, "No /dev/zero."); + fd_zero = open("/dev/zero", O_RDWR); + ASSERT_NE(fd_zero, -1); + + /* + * Map two MAP_PRIVATE-/dev/zero VMAs next to one another with offset 0 + * each. + * + * With these being made truly anonymous upon mapping, they will + * merge. If they were file-backed VMAs the page offsets would prevent + * merge: + * + * |-----||------| |-------------| + * | ptr || ptr2 | -> | ptr | + * |-----||------| |-------------| + */ + ptr = mmap(carveout, 5 * page_size, PROT_READ | PROT_WRITE, + MAP_FIXED | MAP_PRIVATE, fd_zero, 0); + if (ptr == MAP_FAILED) { + close(fd_zero); + ASSERT_TRUE(false); + } + ptr2 = mmap(&carveout[5 * page_size], 5 * page_size, + PROT_READ | PROT_WRITE, MAP_FIXED | MAP_PRIVATE, fd_zero, 0); + if (ptr2 == MAP_FAILED) { + close(fd_zero); + ASSERT_TRUE(false); + } + close(fd_zero); + + /* Assert that they merged. */ + ASSERT_TRUE(find_vma_procmap(procmap, ptr)); + ASSERT_EQ(procmap->query.vma_start, (unsigned long)ptr); + ASSERT_EQ(procmap->query.vma_end, (unsigned long)ptr + 10 * page_size); +} + +TEST_F(merge, merge_map_private_dev_zero_faulted_unfaulted) +{ + struct procmap_fd *procmap = &self->procmap; + unsigned int page_size = self->page_size; + char *carveout = self->carveout; + char *ptr, *ptr2; + int fd_zero; + + if (access("/dev/zero", F_OK)) + SKIP(return, "No /dev/zero."); + fd_zero = open("/dev/zero", O_RDWR); + ASSERT_NE(fd_zero, -1); + + /* + * Map a MAP_PRIVATE mapping of /dev/zero with page offset 0, then fault + * it in: + * + * |-------------------------------| + * | faulted | + * |-------------------------------| + */ + ptr = mmap(carveout, 15 * page_size, PROT_READ | PROT_WRITE, + MAP_FIXED | MAP_PRIVATE, fd_zero, 0); + if (ptr == MAP_FAILED) { + close(fd_zero); + ASSERT_TRUE(false); + } + memset(ptr, 'x', 15 * page_size); + + /* + * Unmap the middle: + * + * |---------| |---------| + * | faulted | | faulted | + * |---------| |---------| + */ + ASSERT_EQ(munmap(&ptr[5 * page_size], 5 * page_size), 0); + + /* + * Map in a new unfaulted mapping in the middle with page offset 0 - + * this should merge and would not if it were treated as a file rather + * than pure anon: + * + * |---------|-----------|---------| + * | faulted | unfaulted | faulted | + * |---------|-----------|---------| + */ + ptr2 = mmap(&carveout[5 * page_size], 5 * page_size, + PROT_READ | PROT_WRITE, MAP_FIXED | MAP_PRIVATE, + fd_zero, 0); + close(fd_zero); + ASSERT_NE(ptr2, MAP_FAILED); + + /* Assert that they merged. */ + ASSERT_TRUE(find_vma_procmap(procmap, ptr)); + ASSERT_EQ(procmap->query.vma_start, (unsigned long)ptr); + ASSERT_EQ(procmap->query.vma_end, (unsigned long)ptr + 15 * page_size); +} + TEST_F(merge_with_fork, mremap_faulted_to_unfaulted_prev) { struct procmap_fd *procmap = &self->procmap; -- 2.55.0