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 7FF89C5B569 for ; Mon, 10 Aug 2026 22:10:16 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 5EC046B007B; Mon, 10 Aug 2026 18:10:15 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 59C866B008A; Mon, 10 Aug 2026 18:10:15 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 4B24C6B008C; Mon, 10 Aug 2026 18:10:15 -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 16D916B007B for ; Mon, 10 Aug 2026 18:10:15 -0400 (EDT) Received: from smtpin18.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 9240614024F for ; Mon, 10 Aug 2026 22:10:14 +0000 (UTC) X-FDA: 85086753948.18.5269206 Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf21.hostedemail.com (Postfix) with ESMTP id 1D3D71C0003 for ; Mon, 10 Aug 2026 22:10:11 +0000 (UTC) Authentication-Results: imf21.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=korg header.b="UwX/Ilov"; dmarc=none; spf=pass (imf21.hostedemail.com: domain of akpm@linux-foundation.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1786399812; 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=/hUK9nmdYQUfhG6ut1/QpR/T7D3LLI4jSc7+bBZ5Ofc=; b=IiJnIbj5uHsHpNGqSB1LXgR6q8pU9lyqyjEz3F8X5RAOEW6rzu4e7ScUhvs/agi7VwTvl6 wewjKoRksUDArD6w4iIRzAVVBWMBkLVda468zLtLczOnHN6GkOLJGVGQBy0kC7SZlZMBK9 TiztFdkV7xcb/DIBidLxwjnM4iDuz38= ARC-Authentication-Results: i=1; imf21.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=korg header.b="UwX/Ilov"; dmarc=none; spf=pass (imf21.hostedemail.com: domain of akpm@linux-foundation.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1786399812; b=X6mpCEx1fGPEOJNwc5J+pbDceL6dMhjXzCGUN/+HCE6oz6yfkSUI8U1ikW90HOgU7WcUX+ N/Lm1tVETRM+ywIN6PbZAx3oMsBjsD0764Spgqt7i4lEPa4v9R98WQ/J5kfs9SFlsm/igz F3kA44T6coHuydM0o7D9tZ8plMXffU4= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 9648A6001D; Mon, 10 Aug 2026 22:10:10 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id AB66F1F000E9; Mon, 10 Aug 2026 22:10:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1786399810; bh=/hUK9nmdYQUfhG6ut1/QpR/T7D3LLI4jSc7+bBZ5Ofc=; h=Date:From:To:Cc:Subject:In-Reply-To:References; b=UwX/Ilov0bIFii9m3iwtL8q7dWNlzT+Wx3UroPo9PylX7if0NcfH9JAavRDAn86dw JNwDAbfcVY3VRo/UBsUbAdQe6WqOiVdxquE1mb7LVSCrY0NRcx31i22SVoR5H3wZ9K Nroa/JyRqqFqLrw3hFrR5C55A7jEiwD4QPiMGP18= Date: Mon, 10 Aug 2026 15:10:07 -0700 From: Andrew Morton To: "Lorenzo Stoakes (ARM)" Cc: David Hildenbrand , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jann Horn , Pedro Falcato , "Matthew Wilcox (Oracle)" , Jan Kara , Miaohe Lin , Naoya Horiguchi , Rik van Riel , Harry Yoo , Lance Yang , Kees Cook , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Usama Arif , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Peter Xu , Xu Xin , Chengming Zhou , Arnd Bergmann , Greg Kroah-Hartman , Christian Borntraeger , Janosch Frank , Claudio Imbrenda , Alexander Gordeev , Gerald Schaefer , Heiko Carstens , Vasily Gorbik , Sven Schnelle , Alex Deucher , Christian =?ISO-8859-1?Q?K=F6nig?= , David Airlie , Simona Vetter , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , Boris Brezillon , Steven Price , Liviu Dudau , Huang Rui , Matthew Auld , Thomas =?ISO-8859-1?Q?Hellstr=F6m?= , Rodrigo Vivi , Masami Hiramatsu , Oleg Nesterov , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Namhyung Kim , Mark Rutland , Alexander Shishkin , Jiri Olsa , Ian Rogers , Adrian Hunter , James Clark , Jason Gunthorpe , John Hubbard , Muchun Song , Oscar Salvador , Chris Li , Kairui Song , Kemeng Shi , Nhat Pham , Baoquan He , Youngjun Park , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kselftest@vger.kernel.org, kvm@vger.kernel.org, linux-s390@vger.kernel.org, amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, intel-xe@lists.freedesktop.org, linux-perf-users@vger.kernel.org, linux-trace-kernel@vger.kernel.org Subject: Re: [PATCH v4 02/20] mm: provide vma_[flags_]is_cow_mapping() and remove is_cow_mapping() Message-Id: <20260810151007.c1cfbcf46d498d2f8ce566f9@linux-foundation.org> In-Reply-To: References: <20260806-b4-scalable-cow-virt-pgoff-v4-0-ab318a350404@kernel.org> <20260806-b4-scalable-cow-virt-pgoff-v4-2-ab318a350404@kernel.org> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 1D3D71C0003 X-Stat-Signature: 6wapmibastqtqeegnbh1jh1pitdp75we X-Rspam-User: X-HE-Tag: 1786399811-822051 X-HE-Meta: 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 FAJZbP78 67Ca4LOkmym32BDWq7nXHG0/Qc2kXB4Rmu2OWqBwKvBvvKNVi9/0u2We12kgR6ME9lPZ5IWnZmcVzlRDG5JubSUwF4RAPjhqDfc2GMl5IDtIinUvFh0nH3k82MKDL/DXozX8OEBbRA/4smxAor3OUqADOh9ylaBr/gIBrilXXiigotaceStLkMzyfLw8imAg5IBibwWH44K4zU4CpVvgKkRScwLEAkHJa0RMHvxyGgzwxHbrFaQuoClCSXnb0wbk/OjrHQQXqP00m6YZYGx/QdCQV2gyMG6cdzavXnfREzyCXzDVT0l1bkua14O0cBwiqKdHmcM0ZO2rlxA0RqyVI93wh0UILgV77oG9WzEd75YMdMFqX3JOW9wJkmY+TCJsmZIgvBTaDAf1vXbfY7unrBiRU+akxbzqMtdzYoi+IAy+zPepxkXSIc4Z4RGqtZvZ2pKv6LPTXOGy/oBg= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, 10 Aug 2026 18:59:34 +0100 "Lorenzo Stoakes (ARM)" wrote: > Hi Andrew - would it be possible to insert the comments added below? Trying > to avoid a respin if possible :) np, like this? From: Andrew Morton Subject: mm-provide-vma_is_cow_mapping-and-remove-is_cow_mapping-fix Date: Mon Aug 10 03:07:02 PM PDT 2026 add comments, per Lorenzo Link: https://lore.kernel.org/ann-vS6MYT9kuXqu@lucifer Cc: "Lorenzo Stoakes (ARM)" Signed-off-by: Andrew Morton --- include/linux/mm.h | 57 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 57 insertions(+) --- a/include/linux/mm.h~mm-provide-vma_is_cow_mapping-and-remove-is_cow_mapping-fix +++ a/include/linux/mm.h @@ -2271,17 +2271,74 @@ void unpin_user_pages(struct page **page void unpin_user_folio(struct folio *folio, unsigned long npages); void unpin_folios(struct folio **folios, unsigned long nfolios); +/** + * vma_flags_is_cow_mapping() - Do these VMA flags imply a CoW mapping? + * @flags: The VMA flags to check. + * + * Mappings which could be CoW'd (subject to Copy-On-Write faults) are + * described as CoW mappings. + * + * All mappings backed by anonymous folios (all anonymous mappings and most + * MAP_PRIVATE-file backed ranges) are CoW mappings. + * + * All other mappings (including all writable MAP_SHARED mappings) are + * non-CoW. + * + * The criteria are !VMA_SHARED_BIT, VMA_MAYWRITE_BIT. + * + * VMA_MAYWRITE_BIT is checked instead of VMA_WRITE_BIT to account for both + * future mprotect() calls which can render a read-only mapping writable, and + * GUP with FOLL_FORCE (e.g. ptrace) which can CoW a read-only mapping. + * + * - No anonymous mapping can ever clear VMA_MAYWRITE_BIT. + * + * - Writes to anonymous mappings do not immediately result in CoW faults but + * may do so after the process is forked or if a read is followed by a + * write. + * + * - Writes to MAP_PRIVATE file-backed mappings result in CoW faults and may + * do so again after fork. + * + * - MAP_SHARED mappings of a file opened read-only are transformed into + * VMA_MAYSHARE_BIT, !VMA_SHARED_BIT, !VMA_MAYWRITE_BIT mappings, so remain + * non-CoW. + * + * - Drivers may clear VMA_MAYWRITE_BIT but do so at mmap() time and cannot + * mark themselves anonymous. Having cleared this flag it is not valid for + * them to leave the VMA_WRITE_BIT flag set. + * + * As a consequence, the anonymous reverse mapping only tracks CoW mappings. + * + * Returns: true if the flags indicate a CoW mapping, otherwise false. + */ static inline bool vma_flags_is_cow_mapping(const vma_flags_t *flags) { return vma_flags_test(flags, VMA_MAYWRITE_BIT) && !vma_flags_test(flags, VMA_SHARED_BIT); } +/** + * vma_is_cow_mapping() - Is this VMA a CoW mapping? + * @desc: The VMA to check. + * + * See vma_flags_is_cow_mapping() for details. + * + * Returns: true if the VMA is a CoW mapping, otherwise false. + */ static inline bool vma_is_cow_mapping(const struct vm_area_struct *vma) { return vma_flags_is_cow_mapping(&vma->flags); } +/** + * vma_desc_is_cow_mapping() - Is this VMA descriptor a CoW mapping? + * @desc: The VMA descriptor to check. + * + * See vma_flags_is_cow_mapping() for details. + * + * Returns: true if the VMA descriptor describes a CoW mapping, otherwise + * false. + */ static inline bool vma_desc_is_cow_mapping(struct vm_area_desc *desc) { return vma_flags_is_cow_mapping(&desc->vma_flags); _