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 A8052C5B543 for ; Thu, 5 Jun 2025 20:24:03 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 3EB0F6B009B; Thu, 5 Jun 2025 16:24:03 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 394EE6B00C6; Thu, 5 Jun 2025 16:24:03 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 2847D6B00D4; Thu, 5 Jun 2025 16:24:03 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id 071E06B009B for ; Thu, 5 Jun 2025 16:24:03 -0400 (EDT) Received: from smtpin23.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay03.hostedemail.com (Postfix) with ESMTP id 7A72CBF18A for ; Thu, 5 Jun 2025 20:24:02 +0000 (UTC) X-FDA: 83522473524.23.119A0E1 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by imf06.hostedemail.com (Postfix) with ESMTP id 956C8180008 for ; Thu, 5 Jun 2025 20:23:58 +0000 (UTC) Authentication-Results: imf06.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=OIAeUrS7; spf=pass (imf06.hostedemail.com: domain of david@redhat.com designates 170.10.133.124 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=1749155038; 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=wGRAUX3Vi4mrKdBS2NEw0LJip1BNYoUgoRIdRDK4JKI=; b=viSjUorBoqVUryr27Mt4hdb9jVJOupLMTaraJ2LmC0G9qc8PlOtq5txtss+aRhgFi0lBzl rr2jszX4Ws2ItIZ93HTXVXtyVdOessbXSGmtVOLxy9WRudPL9giarjnzZGVLiXBS3nk2f9 PxWj/6FHGi0HR2Tj8xi2Gbj4S+CZIJY= ARC-Authentication-Results: i=1; imf06.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=OIAeUrS7; spf=pass (imf06.hostedemail.com: domain of david@redhat.com designates 170.10.133.124 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=1749155038; a=rsa-sha256; cv=none; b=UCvFLKnKqtCw1orUiPFtAORockV0DuUnbi4ntz6Y3kTS/iOi0iSipcozIizVh2GUnaW+GS GNQfZK8q+7Lynhd2HF8eoIaIIzcuO1kV3MMpnz20+sPB72JMSEsVPBXqWf4pFsc5bUchjt uXKmVIQUSviQnGV5opwBh9Tcpfrexjs= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1749155037; 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=wGRAUX3Vi4mrKdBS2NEw0LJip1BNYoUgoRIdRDK4JKI=; b=OIAeUrS7crOh/ovZUsyO00IsplfpfQzq04nrp03sbvkj8L65OZa9ou0C46TJ/b4287BC/k oc9v/r5VVx+CYj/3txmIj0E+we2Togy+liVqRyLQApY23tWpo2NsS6Sn/bx5NAJ5BywjbS s8Cc/tWaF1r+h+6GLpYjmqgADQl1Zzo= Received: from mail-wm1-f72.google.com (mail-wm1-f72.google.com [209.85.128.72]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-64-cnWOu0dsMIWLMcr0_lY7sA-1; Thu, 05 Jun 2025 16:23:56 -0400 X-MC-Unique: cnWOu0dsMIWLMcr0_lY7sA-1 X-Mimecast-MFC-AGG-ID: cnWOu0dsMIWLMcr0_lY7sA_1749155035 Received: by mail-wm1-f72.google.com with SMTP id 5b1f17b1804b1-451e24dfe1dso11072985e9.0 for ; Thu, 05 Jun 2025 13:23:56 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1749155035; x=1749759835; 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=wGRAUX3Vi4mrKdBS2NEw0LJip1BNYoUgoRIdRDK4JKI=; b=qZUBXGw7RFll+gT0RCH04sf+qC61wD3lPvLLlqRPST5I6KmM7862eHVu8l7DerrblN okwdindXC2keDFL7/6OtTqrbSX/yCuviItsC/TgzDql3J+Xr5qaRYomq2VW2hNjI8/wY uGQKj8autZS591Qdjq/ocdBOKeMLONC88i8XT4crF827Xg++92hIK/xgY7FB3XXHCuPi 01B6DYB5pbTbBrPEdXYW8YYf+kr97V7Q8VbGD5xVLju8GRLmpsNp3Io3oXmACjiftnyw wOiS97kBZypvqhosOOJiOFWiSNKKzwaortoNi7L3IVp86EGtVBPPEwlnzZH5/QcZ0oby lDCA== X-Forwarded-Encrypted: i=1; AJvYcCU6s8deODPX/NnfPwTXjEOTex2845qz/+FMp5/dfE0dawL4k908hngnHJEaqQy//i6dlXFUs2se4Q==@kvack.org X-Gm-Message-State: AOJu0Yy2O2f5u9qCK+A58VKjjh+2PrLAbA9xM3vy3+anXe+yQc30P1Kr mhipfxjc4JoLvm5PfsbYCpEKhZdKMph9duvxIjfTmfdwVCDZdsEP/Sew8lxrZ4Ogf+KP4QtSZiz Sq7AkcSZXjHyiENx7aS51jkjO2f9AGxlwOGXjnXHviveUgIe8SK4D X-Gm-Gg: ASbGncto2otRhcHawE2inxbBbV5DZSTGBe8W0rR4Gjh44liH7AMjkd4OmGMTxi9TrAU qvr8zeYKMhrm+pNVzPVOIGIrZWpbCwgFujvcDrAppGPF3qdkUy12S8IeFMMXkwn5qXqs1SfKx2V DbQrfyNUf7zIIgJMmG4OprEukVLIsKFzjxBP+3+XLg3jsjA6Lz1T11GjnOBFYVzasfQDoYB6lPG 5e4qwBmGS78ay/+VBYJOWjIs81YvKwF18kx824KFwDWuLxwfFrXASNRzny5ZAXCB3TdtARdpRg7 kIxs63ovYg8lvhV5m56oUFAZkH2yJewSK/+Bs/pHDo95ssUGvSbhLw== X-Received: by 2002:a05:600c:8b6f:b0:441:b3eb:574e with SMTP id 5b1f17b1804b1-45201437a3bmr7944245e9.5.1749155035365; Thu, 05 Jun 2025 13:23:55 -0700 (PDT) X-Google-Smtp-Source: AGHT+IEiHsw/Y4RMekktDUGS/INXjLuw1e2xyTzcANzwqsfxHShQSLVh4rDvLAoSpveuDwSISxQApw== X-Received: by 2002:a05:600c:8b6f:b0:441:b3eb:574e with SMTP id 5b1f17b1804b1-45201437a3bmr7943865e9.5.1749155034932; Thu, 05 Jun 2025 13:23:54 -0700 (PDT) Received: from [192.168.3.141] (p4fe0f5ef.dip0.t-ipconnect.de. [79.224.245.239]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a532436555sm138250f8f.61.2025.06.05.13.23.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 05 Jun 2025 13:23:54 -0700 (PDT) Message-ID: Date: Thu, 5 Jun 2025 22:23:52 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] mm/pagewalk: split walk_page_range_novma() into kernel/user parts To: Jann Horn , Lorenzo Stoakes Cc: Andrew Morton , Barry Song , "Liam R . Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Muchun Song , Oscar Salvador , Huacai Chen , WANG Xuerui , Jonas Bonn , Stefan Kristiansson , Stafford Horne , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , loongarch@lists.linux.dev, linux-kernel@vger.kernel.org, linux-openrisc@vger.kernel.org, linux-riscv@lists.infradead.org, linux-mm@kvack.org References: <20250604141958.111300-1-lorenzo.stoakes@oracle.com> 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: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: dXfP0L9zfgl9aMJmOwFL8HWTjrmPKiN-rMoVtT-OEdc_1749155035 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 956C8180008 X-Stat-Signature: 3jo9mc4yq189o71ycspjbnn9bqh7ke6q X-Rspam-User: X-Rspamd-Server: rspam07 X-HE-Tag: 1749155038-874804 X-HE-Meta: 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 iuCZJ0E3 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 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 05.06.25 21:19, Jann Horn wrote: > On Wed, Jun 4, 2025 at 4:21 PM Lorenzo Stoakes > wrote: >> The walk_page_range_novma() function is rather confusing - it supports two >> modes, one used often, the other used only for debugging. >> >> The first mode is the common case of traversal of kernel page tables, which >> is what nearly all callers use this for. >> >> Secondly it provides an unusual debugging interface that allows for the >> traversal of page tables in a userland range of memory even for that memory >> which is not described by a VMA. >> >> It is far from certain that such page tables should even exist, but perhaps >> this is precisely why it is useful as a debugging mechanism. >> >> As a result, this is utilised by ptdump only. Historically, things were >> reversed - ptdump was the only user, and other parts of the kernel evolved >> to use the kernel page table walking here. > > Just for the record, copy-pasting my comment on v1 that was > accidentally sent off-list: > ``` > Sort of a tangential comment: I wonder if it would make sense to give > ptdump a different page table walker that uses roughly the same safety > contract as gup_fast() - turn off IRQs and then walk the page tables > locklessly. We'd need basically no locking and no special cases > (regarding userspace mappings at least), at the cost of having to > write the walker code such that we periodically restart the walk from > scratch and not being able to inspect referenced pages. (That might > also be nicer for debugging, since it wouldn't block on locks...) > ``` I assume we don't have to dump more than pte values etc? So pte_special() and friends are not relevant to get it right. GUP-fast depend on CONFIG_HAVE_GUP_FAST, not sure if that would be a concern for now. -- Cheers, David / dhildenb