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 05ED1C5CFCF for ; Tue, 11 Aug 2026 08:41:30 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id EB5AF6B007B; Tue, 11 Aug 2026 04:41:29 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id E66716B008A; Tue, 11 Aug 2026 04:41:29 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id D54536B008C; Tue, 11 Aug 2026 04:41:29 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id AA74B6B007B for ; Tue, 11 Aug 2026 04:41:29 -0400 (EDT) Received: from smtpin13.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 9381C1C0FFD for ; Tue, 11 Aug 2026 08:41:27 +0000 (UTC) X-FDA: 85088344614.13.ADE8E74 Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf01.hostedemail.com (Postfix) with ESMTP id 025864000B for ; Tue, 11 Aug 2026 08:41:25 +0000 (UTC) Authentication-Results: imf01.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=HneO5wKc; spf=pass (imf01.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=1786437686; 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: in-reply-to:in-reply-to:references:references:dkim-signature; bh=B9oyw8VGrdnmKGUbtduBgbxCRdwpvdeLqgkhrCXDNKQ=; b=zUh2ffPdujseIX15scjtukQhf6IacwdRFCbePdSRPlL35SSOMWUPPUxpA5i4Me2l82VQDd 5Nf3ql7r6AMaPmblfEBrkNNbhALgiqOUo/1Tejd02PzFdSihc9Fz7PeA12VceFLweNRiEb J/LdlnFCuupmyoRZ9kyIzW34kSD389Q= ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1786437686; b=FAcv8V2+ZChqrgdhjgUxvOIlckWCfDTlU/a5BztnMYXHYG5NKgJ/G6/jLiYYs/A0Adodle DAkSKkhGVo01TvX/0XgxFsrvHIH3JjsQX/lPNuetR0zkLePzl9K5ElnmEk6LDf5WGuuzfS c3BRl5C/Db19VWY2zKieSxs6xZ9vgmk= ARC-Authentication-Results: i=1; imf01.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=HneO5wKc; spf=pass (imf01.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 747C9600AF; Tue, 11 Aug 2026 08:41:25 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1B8E21F000E9; Tue, 11 Aug 2026 08:41:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1786437685; bh=B9oyw8VGrdnmKGUbtduBgbxCRdwpvdeLqgkhrCXDNKQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=HneO5wKcZdSzCZgiPL7O6y0hkp8NxpOysOwjQ1/0p5DZJDgbHmr8oIIto+qbUqUP8 QSncbqQais7NDR31QFmgQ7SJeueG1RlsaCn/ugXce/uqztMKctFvKx1+vcfyXCvqNZ VJEHlmRInootV9fshr8tYk5LG1afiv/E+UOYl58uNgPRApc4UGU+ngmdh3PqQBdarD Za9aH05yjKoWK0cBkN69Xhhb9cMAk62gCUKpXkd+IC3tlRx4y1qZ5QJ3SYz3eWJwWJ /V1P5kbBwkgzwAFtJUA4uuFpLGZnK495BJYq41HQc15Y/yGaMH9StOXlfO1t3CLsMy Wo0bc8EiRjuEw== Date: Tue, 11 Aug 2026 09:40:50 +0100 From: "Lorenzo Stoakes (ARM)" To: Andrew Morton 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 =?utf-8?B?S8O2bmln?= , David Airlie , Simona Vetter , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , Boris Brezillon , Steven Price , Liviu Dudau , Huang Rui , Matthew Auld , Thomas =?utf-8?Q?Hellstr=C3=B6m?= , 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: References: <20260806-b4-scalable-cow-virt-pgoff-v4-0-ab318a350404@kernel.org> <20260806-b4-scalable-cow-virt-pgoff-v4-2-ab318a350404@kernel.org> <20260810151007.c1cfbcf46d498d2f8ce566f9@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260810151007.c1cfbcf46d498d2f8ce566f9@linux-foundation.org> X-Rspamd-Server: rspam07 X-Rspam-User: X-Stat-Signature: utkyax1eq1bue8z64pgxi5q7onffbzgj X-Rspamd-Queue-Id: 025864000B X-HE-Tag: 1786437685-197516 X-HE-Meta: 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 Sz0NtZMR nUFdhgX7BtERcJKzPYSMS4wKJw5jHPYSxTfOZKVjtElx3iD/ZY/p403TDK8WJ+tkNb58EXR/xsrU5e5ViEAQJlEQCOA0yBeBPY6Dfgc3jEsr2EZ3WMBYykBwTOWGVafiARazRIrlxlPbPmSlHB9jQ/EcYvlta/KOAsT8IX0JaMRfW9PHmNvEQuCzEPLAxJJUBET8uEx1uEdWVjF6u58iOdeBSYi3WKqECWSnodBXfAAz5UxMtWbTzzKxqb3DymWpVC6xoxKPiytV91l3F7QAdBq/HSH67wSLVaXj2+Dx3oLVcxRe4J+/0iHrtg7EP2UiPZFKvnezNGzfb09ynOEtHSFCVbo8K89usM97/Huoa4podyKBUOOy+gelowOMi81eZeYwGIw+kKu+CWqVyurc5YE2sP1oeqrM4EdVZRY4e0QZV19AoYPyuvYXjHKastb3ui2WxkP97+TowPoY= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Aug 10, 2026 at 03:10:07PM -0700, Andrew Morton wrote: > 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? Great thanks! Just one minor edit below (being pedantic here but kinda what the comment needs I think :) > > 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. I ummed and ahhed over how to put this but now I think this could cause confusion so could you replace the paragraph with: * All other mappings (including all MAP_SHARED mappings) are non-CoW. It's _all_ MAP_SHARED mappings not just writable, I thought people would automatically assume read-only wasn't included plus drivers could in theory do crazy things (I have a pending series to fix that though) but it's clearer just to say all. > + * > + * 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); > _ > -- Cheers, Lorenzo