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 525E9C79F82 for ; Tue, 8 Sep 2026 12:53:46 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 6DE746B00BC; Tue, 8 Sep 2026 08:53:45 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 6B8566B00BD; Tue, 8 Sep 2026 08:53:45 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 5A56D6B00BE; Tue, 8 Sep 2026 08:53:45 -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 2DD446B00BC for ; Tue, 8 Sep 2026 08:53:45 -0400 (EDT) Received: from smtpin22.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay09.hostedemail.com (Postfix) with ESMTP id BEEE98062E for ; Tue, 8 Sep 2026 12:53:44 +0000 (UTC) X-FDA: 85190586768.22.CB4D271 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf14.hostedemail.com (Postfix) with ESMTP id E9306100002 for ; Tue, 8 Sep 2026 12:53:42 +0000 (UTC) Authentication-Results: imf14.hostedemail.com; dkim=none; spf=pass (imf14.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@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=1788872023; 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; bh=m900D3UB5BdCkH+JXZv7ve6e2boeFceGJjLp0ABzbU8=; b=PJGFQ/7x8Z/sC5SKuXZ4Fq2qiZz1acD9Pf+ZvjTne7nvE8i+u8GvdhO2fy1iKrkgluswmC An/d3x9F6/tshhjL1aCdy95Mjt9WEvIUQR/l8HwMYO9bepH4b6swvIEz+CPznrFyf9hwPr 1FlXkimpsENoKcNzcs7C2EZtmPXDS0g= ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1788872023; b=fzBZMY9BKN7Cu1wtzdgkY264Io43+oclLNbi9Nrh9ZzjmMlgd/uoI34Sekdz3kXAYFMp8R lFFJzF0unxg2IYG2aECzXaWrwhmSaf+16S8ADBi6J6XvHwX8jEIcJD+kh3/RoTwFD/AUMG Lm97Hycl7Shsyns2eE1SIcfdn5PQCio= ARC-Authentication-Results: i=1; imf14.hostedemail.com; dkim=none; spf=pass (imf14.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 2505C43464; Tue, 8 Sep 2026 12:53:42 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 003FD1F00A3A; Tue, 8 Sep 2026 12:53:36 +0000 (UTC) Message-ID: Date: Tue, 8 Sep 2026 14:53:04 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 4/6] mm/vma: make MAP_PRIVATE-mapped /dev/zero mappings truly anonymous To: "Lorenzo Stoakes (ARM)" , Arnd Bergmann , Greg Kroah-Hartman , Andrew Morton , "Liam R. Howlett" , Vlastimil Babka , Jann Horn , Pedro Falcato , 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 References: <20260908-map-private-dev-zero-v2-0-acc7b5625305@kernel.org> <20260908-map-private-dev-zero-v2-4-acc7b5625305@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20260908-map-private-dev-zero-v2-4-acc7b5625305@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam04 X-Rspam-User: X-Stat-Signature: e8ts5r8g3p8gguca6citci1gr3i9cz8p X-Rspamd-Queue-Id: E9306100002 X-HE-Tag: 1788872022-57271 X-HE-Meta: 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 7hKBhB3e qo/70A0f11DYSyJxX4jhLn+1Gr7FHST8Q7U2RK4oTndpR6tu/gZ1Q6uEn0o+oaOYVxWGPLz6MtH1+jGZvDyTOrV9oH3vbhHzMagWikCxktNqdVXTQO///h7uV/szbC/n7R9TX3T/aX5qP/IML5G1uGsWbPAR0V3s48gAufrL9iMdVM+/1kMy8XFn7bZTjOEQ6vX9HwLQboCMRpNk4MPvjjEqU/Eb072VTq9z7 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/8/26 13:23, Lorenzo Stoakes (ARM) wrote: > When mapping /dev/zero with MAP_PRIVATE, one ends up with strange VMAs > originating from Linux's distant past. > > These have vma->vm_file set but NULL vma->vm_ops, meaning they satisfy > vma_is_anonymous() but otherwise resemble a file-backed VMA. > > The introduction of anonymous page offsets and their subsequent use as > indexes for MAP_PRIVATE-file-backed mappings mean the rmap does the right > thing with these but we are left with inconsistencies. > > The vma_start_pgoff(vma) == vma_start_anon_pgoff(vma) invariant is true for > all other anonymous VMAs, but not these. > > These VMAs are also observable as files in /proc//[maps, smaps, > map_files] but otherwise behave like anonymous mappings. > > Therefore let's make these VMAs actually anonymous at mapping time which > will activate the anonymous code path for mappings. > > This means we no longer have to account for this discrepancy anywhere and > no longer have to think about these at all. > > This is user-observable, as MAP_PRIVATE-/dev/zero will no longer appear in > procfs as a file-backed mapping, but the impact of this change should be > low as likely nobody is relying upon this. > > However in any case, in using MAP_PRIVATE-/dev/zero they are explicitly > asking anonymous memory, so no longer seeing these as file mappings is in > fact correct. > > A previous commit gave us file_is_dev_zero() to positively identify these > mappings, so we expressly only do so for these alone. > > Update assert_sane_pgoff(), the comment for vma_start_pgoff() and > linear_anon_page_index() to reflect the change. > > We make this change in call_mmap_prepare() alone as /dev/zero has been > converted to an mmap_prepare hook and we do not permit nested MAP_PRIVATE > mapping of /dev/zero. > > We also remove the now defunct vma_desc_set_anonymous() and eliminate the > temporary bisection hazard fix from the previous commit. > > Also update the VMA userland tests to reflect the change. > > Finally, update the procfs self tests proc-self-map-files-001 and > proc-self-map-files-002 which both intend to map an arbitrary file > MAP_PRIVATE then assert procfs state, but happen to choose /dev/zero. > > Fix them by updating these to /proc/self/exe which is guaranteed to be > present if procfs is mounted. > > Signed-off-by: Lorenzo Stoakes (ARM) > --- Acked-by: David Hildenbrand (Arm) -- Cheers, David