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 06CE44B04B9; Tue, 8 Sep 2026 11:25:12 +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=1788866723; cv=none; b=lw5iBcZrQ+YxZZFsaCG68Bh7YMtF/z9OcKzRBbXI3gGCooPrylobmSLPu6wD7KbTWkiUeL3hJK98zKWlt0mc0j05KeBv1LnauhEj1vgyEqzrfzVleJA7CTIFe55CdBq0TTb4fqFmW6glBI6PFaAei9KkDfDp+yz6tTM7PZuurXo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788866723; c=relaxed/simple; bh=3png0c8or7nYdCZx23lmGIGRrVIeUt4V+p87b2uuFI8=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=puwvB4UYN21P8aj2geEMouwsm6ykN6j/gCg+WH4u5Q1lS+F+pFIfabD5Za361rBknzYP+j/c0/EbE1xltU5ZjXbxE3U568bFkhqtnIyz5ep5PWOTQkDQ2Q5UVTRDof0NDlZOH4GKDPrqXs1zl3UT74uNrczG7NDvs8QT4sjQt38= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=XgmNxLy3; 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="XgmNxLy3" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7C87C1F00A3D; Tue, 8 Sep 2026 11:25:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788866708; bh=om0np5kv2o7p4ujdr2YodlAc5O6JiCLsFWeQl7Rh24s=; h=From:Date:Subject:References:In-Reply-To:To:Cc; b=XgmNxLy3XXo6zJi+ipSK9/Kxq68nxv16sLLPsIcI4SUgz9twJMZI81MQ1uLL0ZcxC sd97Rux856rODIB4DkQj/J3btopjnfJz8KZCP9qLUOFtDQ2gQaa0TKT3NTVC4GBxU1 sI9BHcnkMlIEvT3Uq5LYGLwZs7FIfAp4e0w3RWiA0yOxITZIYl1/1TqH1gLG9liSBj Kb076kSuPDadjILy/hzduDtUlggkJN6sLYAXYVTZWNmCw9NK5UL2hwjZJMzMYTiv8Z l53JivNcQ3Y6aIvGa6Ww9F6P4pV3Nj1kltUc3JU6Apyk2SY5pGVVxBG5oH77ddyBC0 RtU5Qgx16whFQ== From: "Lorenzo Stoakes (ARM)" Date: Tue, 08 Sep 2026 12:23:43 +0100 Subject: [PATCH v2 6/6] 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: <20260908-map-private-dev-zero-v2-6-acc7b5625305@kernel.org> References: <20260908-map-private-dev-zero-v2-0-acc7b5625305@kernel.org> In-Reply-To: <20260908-map-private-dev-zero-v2-0-acc7b5625305@kernel.org> To: Arnd Bergmann , Greg Kroah-Hartman , Andrew Morton , "Liam R. Howlett" , Vlastimil Babka , Jann Horn , Pedro Falcato , David Hildenbrand , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Hugh Dickins , Baolin Wang , "Matthew Wilcox (Oracle)" , Jan Kara Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kselftest@vger.kernel.org, "Lorenzo Stoakes (ARM)" X-Mailer: b4 0.14.3 X-Developer-Signature: v=1; a=openpgp-sha256; l=4111; i=ljs@kernel.org; h=from:subject:message-id; bh=3png0c8or7nYdCZx23lmGIGRrVIeUt4V+p87b2uuFI8=; b=owGbwMvMwCV2fu7ZrsZH9SKMp9WSGLLmfyh8seHhftu6/WGcCu07NVd5JzsuVNKK1z46e9qze f6bWVjWd5SyMIhxMciKKbI8/yK+P0gkbF7nBX83mDmsTCBDGLg4BWAifVoM/3PfCx6wSxSaVbmk 7+bO4wwSV0UPetSq1M6ULVgWsuaT41aGfwpzf6lGe8wQfcrt4LPt3/Qizd8Nv+V/c+012bGWz6A mhwUA X-Developer-Key: i=ljs@kernel.org; a=openpgp; fpr=E7F417BF5214569E89D04F46CF9DCD8A81E27F14 Assert that MAP_PRIVATE-mapped /dev/zero mappings behave like they are anonymous. Test both unfaulted and faulted/unfaulted merges with page offset 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 anonymous page offsets. Signed-off-by: Lorenzo Stoakes (ARM) --- tools/testing/selftests/mm/merge.c | 95 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 95 insertions(+) diff --git a/tools/testing/selftests/mm/merge.c b/tools/testing/selftests/mm/merge.c index 52b8727b6628..7dd2933417c1 100644 --- a/tools/testing/selftests/mm/merge.c +++ b/tools/testing/selftests/mm/merge.c @@ -1362,6 +1362,101 @@ TEST_F(merge, anon_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 + * the merge: + * + * |-----||------| |-------------| + * | ptr || ptr2 | -> | ptr | + * |-----||------| |-------------| + */ + ptr = mmap(carveout, 5 * page_size, PROT_READ | PROT_WRITE, + MAP_FIXED | MAP_PRIVATE, fd_zero, 0); + 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(ptr, MAP_FAILED); + 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 + 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); + ASSERT_NE(ptr, MAP_FAILED); + 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