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 F076FC624D3 for ; Wed, 2 Sep 2026 18:01:00 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 06D906B00B5; Wed, 2 Sep 2026 14:01:00 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 044B36B00B6; Wed, 2 Sep 2026 14:00:59 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id EC5746B00B7; Wed, 2 Sep 2026 14:00:59 -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 BF1166B00B5 for ; Wed, 2 Sep 2026 14:00:59 -0400 (EDT) Received: from smtpin13.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 4E0EE140205 for ; Wed, 2 Sep 2026 18:00:59 +0000 (UTC) X-FDA: 85169588238.13.01C1031 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf10.hostedemail.com (Postfix) with ESMTP id 6052DC0015 for ; Wed, 2 Sep 2026 18:00:57 +0000 (UTC) Authentication-Results: imf10.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=doxzFlR+; spf=pass (imf10.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=1788372057; b=b018mkQ4PDGCXaUTOcNJRgz7DQHumjarZzN9Tf9710tOKbP07X74kPjLYR4khkmFL7VyWj eO6afXoNBaj2LYeQ8V/HpHIamRJja871EAJCMdlf7XKIf2I0lfcGs+8qPJ1XRYjhezQ+jL G1NxEHCqzyK7xvdABTi+vbZG3MbzxM4= ARC-Authentication-Results: i=1; imf10.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=doxzFlR+; spf=pass (imf10.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=1788372057; 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=jalqcGbTgpiwMOKCsH/rxa3bYllTMGaMYpLwBNB765E=; b=NmNo3QjBwhI9Zw1ZtDgukAaia3Z3JrVu3RA1lYenjX8QH7IouepjKL0Em2ou9hti2La46d m25JiyQGMM7MnR4/c2fIaAX9RUmjITY5pCsk8sXGm0PRLNZeOFXoMwv9Ce1pA/2+R/rYNG swgfbr0EKebKFnr9OSRwktS1xa163Sk= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 8477543240; Wed, 2 Sep 2026 18:00:56 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 618101F000E9; Wed, 2 Sep 2026 18:00:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788372056; bh=jalqcGbTgpiwMOKCsH/rxa3bYllTMGaMYpLwBNB765E=; h=From:Date:Subject:References:In-Reply-To:To:Cc; b=doxzFlR+siE8INCIvg2cvuz6MHpVNZMF68w2lxnCxkffbz1ZHhmabPy8brvZyPiaB QnZToLPbA8CMmcfXQZeQkjbEtUfFMArC1EX06mMDwjMMCckjtZk5t1nxZ8/ZHv0ZAe 1bcr1zeQFzHK+bmBpqwtxYp9gQRp4RiFVGfahnqXT5zTP8gIvKBUNvGrIqJ6QYmbXb GKSkmcJ6lxk7qWSFTH2WfCLTnWRC8noM0Vp8qi8kmAsw0MzXy+DqlaGD7nqJBmTdmN 0cn4w4vj63IRafwXlO9E2GjPAgLcsvqdUKtIomG+HD/Cm3WYilI4HzJgHj36RUbwSQ 34eVzChAWze1g== From: "Lorenzo Stoakes (ARM)" Date: Wed, 02 Sep 2026 19:00:19 +0100 Subject: [PATCH 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: <20260902-map-private-dev-zero-v1-2-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=2934; i=ljs@kernel.org; h=from:subject:message-id; bh=8RUVAZRLPzU4llnS3oLrE03c3Dx8Fmtq1pWNn43ElvA=; b=owGbwMvMwCV2fu7ZrsZH9SKMp9WSGLJmpHiVax5h8JvsqLRXeYlzx+f1kz1m7N39TEJCWcg8e VmK26cXHaUsDGJcDLJiiizPv4jvDxIJm9d5wd8NZg4rE8gQBi5OAZhIXwTDf5esEO3qK6I3JjL+ EF/356EG67sPB9dVcgX1COy/8+d57VSGX8wzGk9dfDZ5g87s/3Mapy92fMJc+C1KQNFpZ1yPUfW MeDYA X-Developer-Key: i=ljs@kernel.org; a=openpgp; fpr=E7F417BF5214569E89D04F46CF9DCD8A81E27F14 X-Rspam-User: X-Stat-Signature: d1j9ypzmd1b6h8313b1hj4745e9t5djk X-Rspamd-Queue-Id: 6052DC0015 X-Rspamd-Server: rspam06 X-HE-Tag: 1788372057-701205 X-HE-Meta: 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 3/1FHklP hTPXEAwMpbkjPp0XC/YCLH3jh1EO4yBBdFjD1hLv3TOv8VLV/UqLecy1lOQWrwa8yaydnjHTqxd1jyMrbaYeOm8DdtIQbNoHiWIECQulIky04B2E6+QoSLpAQEldLsAV4dQoQDMmuPsU31sdWc/Xklfjnttvw/AO3rHNW7xqu8kqtljJnEpFYvCoGP1R66Lm6mMERlyXau367sT+fVh1pc+tGJhmtVcpghrgRTA74m5vxJxjQuzvqf4Dbrjo44BIZjDI4EMH7xiewwG7bYF0efjU8sN4SbTb9eek514/zS5FRCbg= 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. 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