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]) by smtp.lore.kernel.org (Postfix) with ESMTP id E392DC5B543 for ; Tue, 10 Jun 2025 13:44:35 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 663B16B007B; Tue, 10 Jun 2025 09:44:35 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 614E56B0089; Tue, 10 Jun 2025 09:44:35 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 502C56B008A; Tue, 10 Jun 2025 09:44:35 -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 352996B007B for ; Tue, 10 Jun 2025 09:44:35 -0400 (EDT) Received: from smtpin26.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id D61CE160401 for ; Tue, 10 Jun 2025 13:44:34 +0000 (UTC) X-FDA: 83539610868.26.2CB3AE4 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by imf07.hostedemail.com (Postfix) with ESMTP id 2F6244000C for ; Tue, 10 Jun 2025 13:44:32 +0000 (UTC) Authentication-Results: imf07.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=NVo8BxO6; spf=pass (imf07.hostedemail.com: domain of david@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=quarantine) header.from=redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1749563072; 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=x2VmyAImjj4hzOnuu3f/wVygVhYGF647p7FjFNq+/QM=; b=ZjNII4nM9MaQGbxCgYUpsuQK6Q+VHgHyEnQ98xvJ9lViveO6ux0klIfw6sVlRFDAyQYKxg 9OOm/Go5Gr376iAKljLSofI4YWser/g+WE+V3+PF4tS20ky1qWSzsDdZrcQcKR75N3U7il m73vP2OcnpsDxpL1SU8WrRFqIPbO8yc= ARC-Authentication-Results: i=1; imf07.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=NVo8BxO6; spf=pass (imf07.hostedemail.com: domain of david@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=quarantine) header.from=redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1749563072; a=rsa-sha256; cv=none; b=Lv8ohdnlkpcdUGuNdtXi2axhnS9x9x7Klyjseo8hpy2M4oeZ9Uj/44DPdEuD8Qql9LmJy4 QSZFgafD7YLNISsG+d3PU5u16yyK9Q2oYI7QF4Zkz6f/f3SJXpJJHXUIf60VKRnjpW88I/ 9lclJeCa9q+gR2fHh+SYbH0k2t+rZug= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1749563071; h=from:from: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:autocrypt:autocrypt; bh=x2VmyAImjj4hzOnuu3f/wVygVhYGF647p7FjFNq+/QM=; b=NVo8BxO6ypdHU4Z8m18ERCqYPSfV7mxnF9BE8+Va7A8+kZEyu1TcKyAzvBwe9k1VUXYKNF nLiEKPbNtsZ6oLIDnQAlNx+v/K87IxdydXMuKrS5cFNxXq9w817xrwbMc2MRvP3Sh/Kw98 5+O0HGNouUusovXpTQbrrIkvjiDUt48= Received: from mail-wr1-f69.google.com (mail-wr1-f69.google.com [209.85.221.69]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-683-ZrufrhyBMsmJT9uBKIWhHQ-1; Tue, 10 Jun 2025 09:44:30 -0400 X-MC-Unique: ZrufrhyBMsmJT9uBKIWhHQ-1 X-Mimecast-MFC-AGG-ID: ZrufrhyBMsmJT9uBKIWhHQ_1749563069 Received: by mail-wr1-f69.google.com with SMTP id ffacd0b85a97d-3a4f858bc5eso3983055f8f.0 for ; Tue, 10 Jun 2025 06:44:30 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1749563069; x=1750167869; h=content-transfer-encoding:in-reply-to:organization:autocrypt :content-language:from:references:cc:to:subject:user-agent :mime-version:date:message-id:x-gm-message-state:from:to:cc:subject :date:message-id:reply-to; bh=x2VmyAImjj4hzOnuu3f/wVygVhYGF647p7FjFNq+/QM=; b=a/bvc7EbdUAyjf/bUHhVgUDVWjHUqmPVy0ZakmuQuZnzrHw6Cttkh++z1Sg2PiHpSJ 0NQSKoEJWY2cHjUEix7la5+DOH7sWz0A9cxFWgWBwx35b7fxIwvJ49lc7GDTH4SzHjEK hGJNaZPAJdeaD6ntA1kg6rk1RRBWxn+35ZeU6inYlLVfMUAI+DeaLJIM2rrgszvnkDq7 bcHmWD4HkPLYEvPG7GC59eg8jUP/QOceeCVB2lqgmpCfeJtcnnTmValYXLAx+7+AaOAn lMNRZ35oqGB/WawXUYq5FUOAfxjPCJkFkRhVzmd6LnOamK3X04QJTmQj5J0cQ/SejK4z 2d9g== X-Forwarded-Encrypted: i=1; AJvYcCW55OgaNpkFnKd3fEmyXCqMn3r1VMboek/CJ3pXABTFTtx1rhvZbMYk12fH6AojvAfpD0ZBwj5cMg==@kvack.org X-Gm-Message-State: AOJu0Ywc0c2Rv6ecoVtLQh0DorUURHFpQ30yTMxLV8C/acZPZMUaEREq D3/SO1XXKH6ydgmKm7ZYX2tfjUwCMAv3nplIfAGrboUWj5B/mByqL+50uLp5ZMydHP9Pxgnsya7 klHcp3uOt9ysmUySla7nCglAvIAAmNv56vGV4kYa8FIRt+89eEoyg X-Gm-Gg: ASbGncvGREoUmhv4jrD2MFufdpVj0mWCqFbNTNUJElfzryKWL6Z1eUkFral7pJOcWv1 7qWhgutgpwpbHQ3heQxTFXy7rlIq/N6Q9QaTuNFC46iyBlgSpmXWqaY6Uq8lR3JP4RlR6QHCjGf GV32VMjnk22lDq0CxoZEeBQ/U72Fe9GnaUrGzZTdAoH1iCHOJVh7MvC897zyDo7X5PyK+hGW+Jy YslKHIFr+DuSyx0Lch4P7AHgKxgj8vamq/UIHB9bp2srrnIniHGUo8yffsoaMXANNDBy1LQ4oKb 32QmT/NwA2eXROnHjp1BdHwJwFdtl5u7mQsVfAnKLZF+/wohzlynTXc= X-Received: by 2002:a05:6000:290f:b0:3a4:f655:8c4d with SMTP id ffacd0b85a97d-3a531cafc03mr14432420f8f.27.1749563069100; Tue, 10 Jun 2025 06:44:29 -0700 (PDT) X-Google-Smtp-Source: AGHT+IGu/x/Paa24Rvj8SNK0TN6cfVpKUqZgPCpL5Aazl2BPcT87efCPXFP3jrKdeAxwrMIiICtIHA== X-Received: by 2002:a05:6000:290f:b0:3a4:f655:8c4d with SMTP id ffacd0b85a97d-3a531cafc03mr14432395f8f.27.1749563068705; Tue, 10 Jun 2025 06:44:28 -0700 (PDT) Received: from ?IPV6:2a09:80c0:192:0:5dac:bf3d:c41:c3e7? ([2a09:80c0:192:0:5dac:bf3d:c41:c3e7]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45320b16657sm14394555e9.8.2025.06.10.06.44.27 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 10 Jun 2025 06:44:28 -0700 (PDT) Message-ID: <881baf6e-8118-4d09-86dc-09dcf3a3cd02@redhat.com> Date: Tue, 10 Jun 2025 15:44:27 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/2] mm: Allow lockless kernel pagetable walking To: Lorenzo Stoakes Cc: Dev Jain , akpm@linux-foundation.org, catalin.marinas@arm.com, will@kernel.org, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, suzuki.poulose@arm.com, steven.price@arm.com, gshan@redhat.com, linux-arm-kernel@lists.infradead.org, yang@os.amperecomputing.com, ryan.roberts@arm.com, anshuman.khandual@arm.com References: <20250610114401.7097-1-dev.jain@arm.com> <20250610114401.7097-2-dev.jain@arm.com> <970e1b84-7f47-4a51-ad99-4df9026b8f7d@redhat.com> <359668fb-df61-4135-89ee-2675a06a5c1b@lucifer.local> <1c4714bb-97f3-4261-92b7-34223a32e016@lucifer.local> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: <1c4714bb-97f3-4261-92b7-34223a32e016@lucifer.local> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: Q0jGEQgXcqRqZbnbTcudQJUJOfyj3GeAiWYyqPQWvR0_1749563069 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 2F6244000C X-Stat-Signature: ykhjmp87hthbobcta771r947jiymd338 X-Rspam-User: X-HE-Tag: 1749563072-511056 X-HE-Meta: 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 xDC/falM W9x52TjW8kaqvhqAhd85Kgz4jIVbrpLDg2ZwdjArMocyb/IHuUeA1yBrklKHvyx1TNtjPedneu8s0/ljFKOn8wpHffPyyeMzNP99QEkyGMF2fBgttjm2bD61/QyhKGU0D7L54XOgddw1hSDvuOnNQxQSQwqANdtcZFRfRUHPW7FEAYyer7S0xwV5eep1puOznIdYjR+cEy+49xpQXf3MwU07jQHZ/sIPaLCGN71p8QrlAASgij8PF02goHwK0+Q42KLMApAw7/0877GXRG5Q9sxdiVj2pDFRNSL5mUpMymC9w6oyDXPXvwDgq+rqLlzB2s76/Rkz9zczpMIALoJLew0WuOyjIm6stbuHsytGzcYmT1QjuFs4KfAdKsgrdbT79WoOGwLcmVLtTsQokU0ODk+pGx4YyTg9fWgSWQU1cT5Nv4wlHOOSoB+TJUU6HfzdY60u8cI86bA/NgmFHGRfbWA+eFQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 10.06.25 15:35, Lorenzo Stoakes wrote: > On Tue, Jun 10, 2025 at 03:31:56PM +0200, David Hildenbrand wrote: >> On 10.06.25 15:27, Lorenzo Stoakes wrote: >>> On Tue, Jun 10, 2025 at 03:24:16PM +0200, David Hildenbrand wrote: >>>> On 10.06.25 14:07, Lorenzo Stoakes wrote: >>>>> OK so I think the best solution here is to just update check_ops_valid(), which >>>>> was kind of sucky anyway (we check everywhere but walk_page_range_mm() to >>>>> enforce the install pte thing). >>>>> >>>>> Let's do something like: >>>>> >>>>> #define OPS_MAY_INSTALL_PTE (1<<0) >>>>> #define OPS_MAY_AVOID_LOCK (1<<1) >>>>> >>>>> and update check_ops_valid() to take a flags or maybe 'capabilities' field. >>>>> >>>>> Then check based on this e.g.: >>>>> >>>>> if (ops->install_pte && !(capabilities & OPS_MAY_INSTALL_PTE)) >>>>> return false; >>>>> >>>>> if (ops->walk_lock == PGWALK_NOLOCK && !(capabilities & OPS_MAY_AVOID_LOCK)) >>>>> return false; >>>>> >>>> >>>> Hm. I mean, we really only want to allow this lockless check for >>>> walk_kernel_page_table_range(), right? >>>> >>>> Having a walk_kernel_page_table_range_lockeless() might (or might not) be >>>> better, to really only special-case this specific path. >>> >>> Agree completely, Dev - let's definitely do this. >>> >>>> >>>> So, I am wondering if we should further start splitting the >>>> kernel-page-table walker up from the mm walker, at least on the "entry" >>>> function for now. >>> >>> How do you mean? >> >> In particular, "struct mm_walk_ops" >> >> does not quite make sense when not actually walking a "real" mm . >> >> So maybe we should start having a separate structure where *vma, >> install_pte, walk_lock, hugetlb* does not even exist. >> >> It might be a bit of churn, though ... not sure if there could be an easy >> translation layer for now. > > But you know... I looove churn right? <3 <3 <3 :))) > > That's a nice idea, but I think something that should be a follow up. Yes, absolutely, just wanted to raise it :) -- Cheers, David / dhildenb