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 AE414C79FA1 for ; Tue, 8 Sep 2026 11:24:58 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id B989E6B0096; Tue, 8 Sep 2026 07:24:57 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id B70E46B0098; Tue, 8 Sep 2026 07:24:57 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A86C66B0099; Tue, 8 Sep 2026 07:24:57 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id 8947D6B0096 for ; Tue, 8 Sep 2026 07:24:57 -0400 (EDT) Received: from smtpin15.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay03.hostedemail.com (Postfix) with ESMTP id 083A6A0534 for ; Tue, 8 Sep 2026 11:24:51 +0000 (UTC) X-FDA: 85190362824.15.E995607 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf24.hostedemail.com (Postfix) with ESMTP id E6773180006 for ; Tue, 8 Sep 2026 11:24:49 +0000 (UTC) Authentication-Results: imf24.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=J2vGBeCe; spf=pass (imf24.hostedemail.com: domain of ljs@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=ljs@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1788866690; b=e1+X+S143wxiKxeOwoK0tX2KcxjutK9/eGadWDeSxgMkupegKb6Vvc2lob+XANluII8+Op icPNLoh+wc7pqRWSaaKmudggEcTotgviXsGb1fNZDggv9kAIsktLW1KJ4dSxBwLC4CHmRP dL92WPvXmypYEuzY8mh5DXGKZre2rj0= ARC-Authentication-Results: i=1; imf24.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=J2vGBeCe; spf=pass (imf24.hostedemail.com: domain of ljs@kernel.org designates 172.234.252.31 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=1788866690; 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=ZD8suF3oBkRiBnGMYK6L0aQ8GBQOf0jcBYGbzi2Nc77nVkPLmtF0DUyDWHczuH40XYmBs1 nxvKRsubZoecmsK9z2Rn2tdZZXV9SrRtaFGzv4HnncJZleHootoGcxqxRn5jRJ/ythFN5z JFeuBLmi09PvhUSa7XPlYWp4qtYGEB8= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 36D2643F4D; Tue, 8 Sep 2026 11:24:49 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3BDD01F00A3E; Tue, 8 Sep 2026 11:24:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788866689; bh=QpNjJERy5W0kZ4sRAK5DqssDq5giEzAZ8nJVAHeIm7A=; h=From:Date:Subject:References:In-Reply-To:To:Cc; b=J2vGBeCewZOhjQLLB49PJxkgMpsXWdqjwH7GKarj61WbzSCS1NNO2oOQt9HIjm5rp u4jBuYPhwsTKgB+LY7E6DrAtdeh0+kGQ3XDJWk7P0/J2tjJsGgcohsLg2gKViHhNlT HMFNoovZtWaYxqigrBGQwQWaruFMVFkX1H2eaxW0fwKlrWxRnCV4nN7oni97TZAioY TJLnyC7f2dfjBY0gWgs6vUpEXWkx3E/1Lw5j5O3IVuGxhkpAd11PqQ5sOuK9XCZAMg QITnixPPxa7aTS1r4Rlbke1xMxw/oZ1ABhd2RJT4b5lDuWyN1TlNRdT8lQKtXXYMWZ 0BYDV6/5X6ROQ== From: "Lorenzo Stoakes (ARM)" Date: Tue, 08 Sep 2026 12:23:39 +0100 Subject: [PATCH v2 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: <20260908-map-private-dev-zero-v2-2-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=2988; i=ljs@kernel.org; h=from:subject:message-id; bh=A0bJ64HW79psSPlOLCnw7EMt+8G8UJeBpFvBmWrksO0=; b=owGbwMvMwCV2fu7ZrsZH9SKMp9WSGLLmfyjcGSSo1Re24du3VUcC7M8aau83dRc+0TDx5cfHI VMDs27xdpSyMIhxMciKKbI8/yK+P0gkbF7nBX83mDmsTCBDGLg4BWAihUEM/+PWJrT9WRQRY19Q ZWlws69zynZdjsJ7BoFxXr+urndleM7w36O0/4+4w8YDU5d/DppydP6UKZdnc2258yTK5umRjr+ Nq3kB X-Developer-Key: i=ljs@kernel.org; a=openpgp; fpr=E7F417BF5214569E89D04F46CF9DCD8A81E27F14 X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: E6773180006 X-Stat-Signature: mr4et97e6iaf4996i33hd8zdy4cz9p3a X-Rspam-User: X-HE-Tag: 1788866689-786551 X-HE-Meta: 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 oXTZ/W2g V3x4miFBs1ZKtNhiBRmwnf+UK8GKSh2pGwApyYiDtNM6SWuqquHThMTc8id2d9BWLDVlk4QmSTwD+Ms5W9y1C4a4PRqZTuJMENRa75AD1fSWzLnpNm4KRbf9PdxrcVuwKOjcyMWvrBpWDjpMTSz62epoxAVoPqIJUv1GhYmDbr1/3gRLBW8uO1bwvaj4N94io2MTgz1Gv6nYgbIxVZFj5ohMbfvO5bhRQm9LTVrvTNzEZ1TMKd9mZ8JeWmiltZ4kVS0mUvfo52jEDloz0XRNnxDYd9RNs4G5rdhZqP0iR2IAqH34= 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