From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 6407CC98332 for ; Sat, 26 Sep 2026 10:41:35 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 7950F6B0092; Sat, 26 Sep 2026 06:41:34 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 76D236B0093; Sat, 26 Sep 2026 06:41:34 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6AA8F6B0095; Sat, 26 Sep 2026 06:41:34 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 4F6C66B0092 for ; Sat, 26 Sep 2026 06:41:34 -0400 (EDT) Received: from smtpin30.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay06.hostedemail.com (Postfix) with ESMTP id D1C03A6CAD for ; Sat, 26 Sep 2026 10:41:33 +0000 (UTC) X-FDA: 85255572066.30.3CFC331 Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf09.hostedemail.com (Postfix) with ESMTP id 15A31140006 for ; Sat, 26 Sep 2026 10:41:31 +0000 (UTC) Authentication-Results: imf09.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=bf3UH823; spf=pass (imf09.hostedemail.com: domain of ljs@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=ljs@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1790419292; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=QpNjJERy5W0kZ4sRAK5DqssDq5giEzAZ8nJVAHeIm7A=; b=rDGgJ8TSx2yXAfd4pzzlpoEIbk2ilyF05moqxAcClGBrZS/8qa6ZZgL81Ly6jLwxhghhez sqkkQXrP1PRugghKQkwMdRkD5COTVQM3ocbzqZC5TT9L/5LBsVJjFZwB7E0cMlKKWxWXY3 /f1Eco+xLJiZ91VcY8nFCiMVqrsHuW0= ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1790419292; b=pO/oLdHnJySVsUNSboM1CrkYtQ8n++0VmsxBobfCwwXaYTICWRoYUSuaCrWCLggSxo7pRO TzhlzUWv4m09ZpnsnXQnbfyC1HJqAeIg0bRemixYoHcJsW8ndFsd7V3jPDPFHaZh6d7rPb l3wRPC5zvepF0XtrD2ve27q8FomlHRY= ARC-Authentication-Results: i=1; imf09.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=bf3UH823; spf=pass (imf09.hostedemail.com: domain of ljs@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=ljs@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id ABCC7602C8; Sat, 26 Sep 2026 10:41:31 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 051C41F00898; Sat, 26 Sep 2026 10:41:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790419291; bh=QpNjJERy5W0kZ4sRAK5DqssDq5giEzAZ8nJVAHeIm7A=; h=From:Date:Subject:References:In-Reply-To:To:Cc; b=bf3UH823SDyPigbs7RNHaNH2jKNNG8Cihq4p8htIHOFP0y5JPaxJKzygUs/G0S41+ qvH12ic20EaJ9etadHm39FyDSWwS/1JqRu3taTIBWeIhsTJNSXxxULGOc1zSRZU1e8 /NkpnZRm2YbTo5anSZ3jMGIiuSo/Wj6yes7xyynt+PFF7DD8i+JRTRkF4pJCWaqw10 YXLw3YB193YrQs0PmKXPMMgvy6eJ1hMGZOeQBbFCQbOFZpAXXIAsss//DISRZ+S18w oD1HDq0RdLj6II9up3zANivAUvWWKAN84FV03dw2h7iZcA3DR2dpboP2KN2P4SXG4U 2J+uMGvjwkokQ== From: "Lorenzo Stoakes (ARM)" Date: Sat, 26 Sep 2026 11:41:07 +0100 Subject: [PATCH v3 2/6] mm: implement file_is_dev_zero() to uniquely identify /dev/zero MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260926-map-private-dev-zero-v3-2-d4781e84ccfc@kernel.org> References: <20260926-map-private-dev-zero-v3-0-d4781e84ccfc@kernel.org> In-Reply-To: <20260926-map-private-dev-zero-v3-0-d4781e84ccfc@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=2988; i=ljs@kernel.org; h=from:subject:message-id; bh=A0bJ64HW79psSPlOLCnw7EMt+8G8UJeBpFvBmWrksO0=; b=owGbwMvMwCV2fu7ZrsZH9SKMp9WSGLK2L/SZUz/xt+YCHmOZAPNVR/emF+mUGhpznuz9NHu/+ ZlfkYv7O0pZGMS4GGTFFFmefxHfHyQSNq/zgr8bzBxWJpAhDFycAjARUUNGhofakp8W1xypEPqm YdMh/+jFtb13zgT8z7tm055uai8VZM3IsF4kyNlMPifU9laL+nZRr5jX7YHa1pt04kysJuazPJb mAQA= X-Developer-Key: i=ljs@kernel.org; a=openpgp; fpr=E7F417BF5214569E89D04F46CF9DCD8A81E27F14 X-Rspam-User: X-Stat-Signature: piaeys5mi1ey8yx56exckiyw6s16s1kp X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 15A31140006 X-HE-Tag: 1790419291-506156 X-HE-Meta: U2FsdGVkX1+Z1OXmy7yg8/K/xuhL0yMQu8srxZRXaZqKwdDAocCpkUJr1l/K/kHEyE/EdDImNrhKY5igyqB5IOAThhJyI8R4rk9rDYJv0BGxXPl0A77GQLwegHVH3KOR45qIgPzG0mH73vmxBQKtvOCM14y4OKcmjV72ktyb3JltceIFJfeZon5fLmaO5e36HgwIHRBG+qEAPKX+KK/wu3kaibESWNBTiSGalu8p/bwAVerxNys0A1rBSEMrCfkrIMkcsPvyq0e9DI8glkxTV4gn+p3/uYZ8t38EeZN4t0Md5wqgmB/fp4aQR1SSAWFJ3VMAA/7XBlNBt1k7GBTSmVUecM3zetkQqlY5zu18alGFcgGOk1xR55GwnZZbuMLwFbE3LdqfIldq7pGv2zE5HS58tyVWpWWqd3d8pLdia+XTU6dbfKAhU4KwwQo2TJd7R6O6GyEID399d4Qqtqmbib9CpH2auhOegO6lp1Rms+8RuPEMF8LAP+hf4SZ5vqVhExDO5eVYPx87u5LjvaisAQdU/XjsNqHMRNJqMV60T7cM6KmBH4j/08VOHN10/KoIcIidSeC0GY1lYqpswK2Enex5D1pq2JEo25Br7hxpQ12RppVXMPewwmKRRTVQaGvTQSi2+2SlDG4lmsnOIvsTr/S4v+CDLbGkhPyPEZjRJLaLNxsycnQevdOtCR3kWXt/untpYl0wrYe4pl7XsNgUvrQvkKsqqcOq8kuCcfHSc94iE9EJfRK54IgoOr8mj9KBwEC5YXrArMDW5ZMZ0NlpEciTpihEsdK4lDIARYi+V1ZxAyr4Y11dZiZgHqCxh+URQOzug9iKcHpF71ZzhQ+yUaP9kt2b4UonRBuU4aaoHIDRbAnSUWJuTx+YBhipln3oAkxbnVh2ZgAMxjxvCelgc1leb2zXdIa+urckhLSj0ZVPlbXBNuTm3scSwKLGzrg4FSND450D8o1n6GcnAiZ CUEJDlJ3 jKa095q+x56Rilpn/6Q/Ix1/zytB4WEsC2oPFzAyqdxn/mrWXAGNcZHFVeAlCmO5biJBZ6N/7Oy8/JrXtfhQY1WZUROUXjFxijAEiBozPc08GNL221hPMiIw8dY1jVYrJdhZRe4Bmik37YDAAyxpPX5vNFsQHyS2RBM2sGVFjU6QVsbRYJwP+wkmojyFBUVU5/Wr+Nl0t+xiYu0v8Hgfv+uPcNYTOMEm+UL6VWWLtNDpSOm2lUlWBTPcV4iycH+CHjDhHXZ2rGZdUFGQTDysp2IvJIDRaOAfawgM9 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: To lay the foundation for a future change that converts MAP_PRIVATE-/dev/zero mappings to be truly anonymous, add the ability to uniquely identify these mappings. With the memory character device now part of mm/ this is trivially achievable through a file_is_dev_zero() predicate that simply tests that the file operation hooks are zero_fops. Also update userland VMA tests to expose file_is_dev_zero() and provide a stub zero_fops for testing. Acked-by: David Hildenbrand (Arm) Signed-off-by: Lorenzo Stoakes (ARM) --- mm/char-mem.c | 13 +++++++++++++ mm/internal.h | 3 +++ tools/testing/vma/include/dup.h | 7 +++++++ tools/testing/vma/shared.c | 9 +++++++++ 4 files changed, 32 insertions(+) diff --git a/mm/char-mem.c b/mm/char-mem.c index d2e575545044..e53e89e6ddd8 100644 --- a/mm/char-mem.c +++ b/mm/char-mem.c @@ -31,6 +31,8 @@ #include #include +#include "internal.h" + #define DEVMEM_MINOR 1 #define DEVPORT_MINOR 4 @@ -707,6 +709,17 @@ static const struct memdev { #endif }; +/** + * file_is_dev_zero() - is the specified @file associated with the /dev/zero + * driver? + * @file: File to test. + * Returns: true if it is, false otherwise. + */ +bool file_is_dev_zero(const struct file *file) +{ + return file && file->f_op == &zero_fops; +} + static int memory_open(struct inode *inode, struct file *filp) { int minor; diff --git a/mm/internal.h b/mm/internal.h index e16f1250b25c..5d474e5f7709 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -1638,4 +1638,7 @@ static inline bool can_spin_trylock(void) return true; } +/* char-mem.c */ +bool file_is_dev_zero(const struct file *file); + #endif /* __MM_INTERNAL_H */ diff --git a/tools/testing/vma/include/dup.h b/tools/testing/vma/include/dup.h index 57046d8ac81d..0d1a2ac88922 100644 --- a/tools/testing/vma/include/dup.h +++ b/tools/testing/vma/include/dup.h @@ -1641,3 +1641,10 @@ static inline pgoff_t linear_anon_page_index(const struct vm_area_struct *vma, return pgoff; } + +extern const struct file_operations zero_fops; + +static inline bool file_is_dev_zero(const struct file *file) +{ + return file && file->f_op == &zero_fops; +} diff --git a/tools/testing/vma/shared.c b/tools/testing/vma/shared.c index 4a39c9d50489..8c4826499f40 100644 --- a/tools/testing/vma/shared.c +++ b/tools/testing/vma/shared.c @@ -12,6 +12,15 @@ const struct vm_operations_struct vma_dummy_vm_ops; struct anon_vma dummy_anon_vma; struct task_struct __current; +static int mmap_zero_prepare(struct vm_area_desc *desc) +{ + return 0; +} + +const struct file_operations zero_fops = { + .mmap_prepare = mmap_zero_prepare, +}; + struct vm_area_struct *alloc_vma(struct mm_struct *mm, unsigned long start, unsigned long end, pgoff_t pgoff, vma_flags_t vma_flags) -- 2.55.0