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 97202C5B567 for ; Mon, 10 Aug 2026 18:00:13 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id B34DA6B0092; Mon, 10 Aug 2026 14:00:12 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id ABE3E6B0093; Mon, 10 Aug 2026 14:00:12 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 986E56B0095; Mon, 10 Aug 2026 14:00:12 -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 6AF7A6B0092 for ; Mon, 10 Aug 2026 14:00:12 -0400 (EDT) Received: from smtpin27.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay09.hostedemail.com (Postfix) with ESMTP id D5E1380226 for ; Mon, 10 Aug 2026 18:00:11 +0000 (UTC) X-FDA: 85086123822.27.F41A929 Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf02.hostedemail.com (Postfix) with ESMTP id 4A50C80017 for ; Mon, 10 Aug 2026 18:00:10 +0000 (UTC) Authentication-Results: imf02.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=kBSXhKSR; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf02.hostedemail.com: domain of ljs@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=ljs@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1786384810; 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=1sdXv4xgfeUVqAkpU1fhBBhdTAgllYojDtNDqgM1IHk=; b=r2Hbg3KrVPagriv2ffKC3Q+FjRex+3vJXzsLcWE14HAG4SLZp//chIOQJ2U84ip/noL84C kW76ckrRNzTgtQlUN8mb8ZhyM6SYhwlecPN0k/0R/WYjgNTVhFEcghWJh+fyufld254v0w WmZcqPmUIq5NOGYs2l22EfOt5iVnxpM= ARC-Authentication-Results: i=1; imf02.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=kBSXhKSR; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf02.hostedemail.com: domain of ljs@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=ljs@kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1786384810; b=XUdGo+0Tsbk79MpnMJxaAM/U1mV0jiB4fNMRi0V0q+3IETX46KYQ8+hkmCoHNAVouNwZw5 2HIrR/vj9tmmvkO7MxpsThdFerTpXBAxhNsvigh/ub8TPLSRzBYHjHOGWUpK4XjRaD7/9W EK5XHgIuj0sQY4WEk4MHLN7sKpYjxgo= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 4393B60120; Mon, 10 Aug 2026 18:00:09 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 565781F000E9; Mon, 10 Aug 2026 17:59:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1786384809; bh=1sdXv4xgfeUVqAkpU1fhBBhdTAgllYojDtNDqgM1IHk=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=kBSXhKSRIsXLC0eByPE+1UnsHGha7VR9YSeS1HE4WddrT+XUgckH4QaSZNBUSvJBz d2DQsNEnkdz0fAI9jVlPigkinUU+sqa2swiZ7OMqNx7lIMK0gMPRWg2UyAbaUiy+Cn aC8gIyLrUtkoYxh5mqTArrnu/6NdS/OZBGb71LeYxpP1/wD/GO+iT18lRLEMm9r7O0 fTakaW72WqyHuGbQcmcqhkwnc3yMrTYqPPselQj2nJqDAcyQhNZhevMpKg0vRL9tCd S1En/+odNMPzySWeE2/TMPnoCxK3i6PbK2bhoE8RPTLqhrOElHYd00mTnJ6EXB5qhP 6HROY2mE8TluQ== Date: Mon, 10 Aug 2026 18:59:34 +0100 From: "Lorenzo Stoakes (ARM)" To: Andrew Morton , 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 Cc: 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260806-b4-scalable-cow-virt-pgoff-v4-2-ab318a350404@kernel.org> X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 4A50C80017 X-Stat-Signature: rnp8rkt8znydnkm7gs7w9qptf3w4xx4s X-Rspam-User: X-HE-Tag: 1786384810-178045 X-HE-Meta: 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 zt7ioVvt 5UATxnEcRBbOvTWqfiIkM6iyXpE99oP2ldxig8CNRF1H5dS0+JS01LjZIUaQT1b9fGfmJkvwt6P1ssqUx17wlQeBQX4f4zLSxQ/hPV3SwWzOZ7EOXdVSRbgP6sPJhb+dzAVryLsPxOM7bCe/ATyAwbKqdpJ69/TKVXQzv+bqVJD/leT5vHi42owoZLrbdytkSD+Gw/F+pz8X6ru21HM8pwHFUp53AFj9AqZxywZT+SXMSKEFzuK0CaOYMcg/HxAMq6sCMUCaSogVXxfu06chHsKRty7AmE4lL/YD2W9PTOUDNiP3lAN6RwqqHK5xKV34Pg6X2sNJgZhjsYX4ZTQI9LD1HgftN2XlDXh4ZsmjLWZBit39+SAHtW0ar1g== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi Andrew - would it be possible to insert the comments added below? Trying to avoid a respin if possible :) On Thu, Aug 06, 2026 at 09:21:27PM +0100, Lorenzo Stoakes (ARM) wrote: > diff --git a/include/linux/mm.h b/include/linux/mm.h > index df78847f5f07..a3368c542947 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -2271,17 +2271,20 @@ void unpin_user_pages(struct page **pages, unsigned long npages); > void unpin_user_folio(struct folio *folio, unsigned long npages); > void unpin_folios(struct folio **folios, unsigned long nfolios); > > -static inline bool is_cow_mapping(vm_flags_t flags) +/** + * 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 (flags & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE; > + 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_desc_is_cow_mapping(struct vm_area_desc *desc) > +static inline bool vma_is_cow_mapping(const struct vm_area_struct *vma) > { > - const vma_flags_t *flags = &desc->vma_flags; > + return vma_flags_is_cow_mapping(&vma->flags); > +} > > - return vma_flags_test(flags, VMA_MAYWRITE_BIT) && > - !vma_flags_test(flags, VMA_SHARED_BIT); +/** + * 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); > } > > #ifndef CONFIG_MMU -- Cheers, Lorenzo