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 0F44647605F; Wed, 2 Sep 2026 18:01:14 +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=1788372076; cv=none; b=HajgkRdVKR3COmQ+scdjcAqzZ4pr0dtgCE5DqSjp/UhhBiaWYxQGas8NN+Auh7xOraQxgAOgqvWxnsuF37Fy/xcJo1rUsVQc3kJ7k1MX45ZcejyI5R5gDQNTJdVvCtDdkP82ed0ujJ/gyU9TYPgpMHz8ALmU2rhhh1mg8Pe20Fs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788372076; c=relaxed/simple; bh=6y4SgQpQz3RLpexZGYRim0KFzXiNKV69KBfjEhHHVH0=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=rxfRu20I+rJ+oIHJgPM5yvqe/e6EaEDQG7NekddmwtQ2USNwqa2ojyhiC9Cdbe1mtF7qQucdeWRlfNKV+74HHyHe7q5UV6vSf04uBKbpAGEygFQyClnmBZvRophOZNhuVAmPLLEZzjxeVWIexC57z/6qJbTwOhz1tkW4cG1HB4I= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=d1FKV9YY; 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="d1FKV9YY" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 72A4C1F000E9; Wed, 2 Sep 2026 18:01:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788372074; bh=gKMN/4ga+akQkR+gCUDsGByPhFMGOkvrwnVsmryglD8=; h=From:Date:Subject:References:In-Reply-To:To:Cc; b=d1FKV9YYgYwhR45HYlw7ao5vs9Wvz7PH7HdW6abQ3+PLbGWWvZo+3YkL2712FNcj3 eFB3FqAWjSUj+yOdKG8HVSn91Hj33qCCBkTf4fY5KlCUwk8LWC/p+mBfsSR5DnKUiv zhJY6+WmVzQqCI3nQq9Be6MCrPz/Eynxla55ntnaJM6OZU/sEqproc8yvTFMEcQWrQ eG87GbKzRQfMfugp1SyOaQoerezIFaaZibVV2aRufhYlYB6wVAJNTzBiQo8Z/9TAeJ 6/I5figxrew5gszJrQH9r3n1eOfh3ulOJKEDhuPwsCKtrOg0tOiipteEvSpi0Rzec2 kmSKNsyOBD/9Q== From: "Lorenzo Stoakes (ARM)" Date: Wed, 02 Sep 2026 19:00:23 +0100 Subject: [PATCH 6/6] tools/testing/selftests/mm: add MAP_PRIVATE-/dev/zero merge tests Precedence: bulk X-Mailing-List: linux-fsdevel@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: <20260902-map-private-dev-zero-v1-6-a578c730cec7@kernel.org> References: <20260902-map-private-dev-zero-v1-0-a578c730cec7@kernel.org> In-Reply-To: <20260902-map-private-dev-zero-v1-0-a578c730cec7@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=4280; i=ljs@kernel.org; h=from:subject:message-id; bh=6y4SgQpQz3RLpexZGYRim0KFzXiNKV69KBfjEhHHVH0=; b=owGbwMvMwCV2fu7ZrsZH9SKMp9WSGLJmpHjNspi7c//R9qnWvN3MzKq2h9cVHb91el5GlePJx AUbDF6/6ShlYRDjYpAVU2R5/kV8f5BI2LzOC/5uMHNYmUCGMHBxCsBEWhMZGa6e/NO3dpKZDHd8 SbPov0Khpf26ryc8Xx3y77RUo+xE11UMf6XV3rybEF3BPn1ybYZMjtSSYidPjSe/6r7wZV45bLb gGxcA 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 anonymous 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 52b8727b6628..7c528d470404 100644 --- a/tools/testing/selftests/mm/merge.c +++ b/tools/testing/selftests/mm/merge.c @@ -1362,6 +1362,110 @@ 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 + * 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