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 1EB0DC3DA49 for ; Fri, 26 Jul 2024 16:02:27 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 784F26B0082; Fri, 26 Jul 2024 12:02:26 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 734126B0096; Fri, 26 Jul 2024 12:02:26 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 5FC416B0098; Fri, 26 Jul 2024 12:02:26 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 4221A6B0082 for ; Fri, 26 Jul 2024 12:02:26 -0400 (EDT) Received: from smtpin04.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay06.hostedemail.com (Postfix) with ESMTP id D02F9A3628 for ; Fri, 26 Jul 2024 16:02:25 +0000 (UTC) X-FDA: 82382371050.04.8777986 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by imf14.hostedemail.com (Postfix) with ESMTP id 7A71210002C for ; Fri, 26 Jul 2024 16:02:22 +0000 (UTC) Authentication-Results: imf14.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=UIpoPOVY; spf=pass (imf14.hostedemail.com: domain of david@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1722009692; 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=7T1zmTBwVGz0bXrlRqWcRFYDeuwstSfgw5YyJGwg+80=; b=WCARE/h6sx7X8dYa6VdmxRfMDBcDBo1mXfsI6iWdFEe2hAI5jCIX2P3drRD+vsK9CVwbkJ Dx7z5oXB9ibl80xspHJrxt8BY5EHjxH9XHDc0JLEZrI1WUBvjkkJpO0LUmSMufBFYbH+z8 JQVabKzJ84yzTqH4jmgBYzyJTQ2pOmY= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1722009692; a=rsa-sha256; cv=none; b=ZlI6GrzjCwqbEToTMFFTZpTI333LhWpTsFzD5Yv/JyWcWXwSjkaKugER3h81S5Y6uQcUgw Kl5dS/0Ybl2sEauzQhFPpF8xIAfqTSJMY1mgLbSQQg0CeM7wd80UFwLEKjQk9G5Bh/eN8K XtsK7jihScJVkFoL3ysp88uaimObuTo= ARC-Authentication-Results: i=1; imf14.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=UIpoPOVY; spf=pass (imf14.hostedemail.com: domain of david@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1722009741; 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=7T1zmTBwVGz0bXrlRqWcRFYDeuwstSfgw5YyJGwg+80=; b=UIpoPOVYLF0DtLDbFPLgU6LIWMRGWWvWFUo35YgmfGcRb7+NNtgX/5YfGrukcSL+6MHoid OQzPWIyQnQ/YLHT8FZcXaDRZ1wgUSKhC7dNpcm2vZLUXHoRYt3dlW9Jn9Pjgbe+d/PYBDq t4Tgoeg230VqOw9ek7UhYqdB45M8pSY= Received: from mail-wm1-f69.google.com (mail-wm1-f69.google.com [209.85.128.69]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-122-QgXGkO55POCVNWyWQc-pCw-1; Fri, 26 Jul 2024 12:02:20 -0400 X-MC-Unique: QgXGkO55POCVNWyWQc-pCw-1 Received: by mail-wm1-f69.google.com with SMTP id 5b1f17b1804b1-4280cf2be19so5952765e9.3 for ; Fri, 26 Jul 2024 09:02:20 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1722009739; x=1722614539; h=content-transfer-encoding:in-reply-to:organization:autocrypt:from :content-language: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=7T1zmTBwVGz0bXrlRqWcRFYDeuwstSfgw5YyJGwg+80=; b=CnNoIm5t6oerApizGxuh9G9PWTHkCAlGILcGgJOVJRDpWVjh+nqmeXl3CthY6uSO4S wXdFgNq7jwJOG/7ltPRNXCBUr3vZv1vXONOuuXgPwoGvGCq7jftQ64OXoZsp2FwXFPnq u3rmNWpe9hD/Vzg/EQmTmFoCVVm7eoy2gTD1+fhSvFF01U0ievrjcqp55iaO+EzRFErs O6R36sgdDctG6jf6nqUE6JYE8IFvowphsd8WOH2yd8cdd/G4uprxE7x84mArgfpVVPOg dLCZY/wfbZbpMQAax6+BjwWl7WxXlf85qXeltMXr+qq2co7eH/n+sRkFdhZXrV40U+U5 lyIQ== X-Forwarded-Encrypted: i=1; AJvYcCUGk5nqWf0Loo220ykY14sCc5HSwUqntLvC90/C6SYcKgV2jqaHV2vfjURH0BxIAhktvbpNEpzwdAMR4HjgtnglcIo= X-Gm-Message-State: AOJu0YxGXUK73TeWL0jjlX2qYlFHqBwIs/y3N16YKNZNCmwjwek1X/2k vjwuYBnfhCgSF7kk96H2PePHL50VBn0w5oUm0gmGMaGnXEw5AoywGyJM9lGCowcsl/F9tSy2tsX 2K0SGLk+ohjZh36fXSJzLQGWVuUcoxkm26ZvoJ+2a35ziEqCk X-Received: by 2002:a05:600c:4443:b0:426:62df:bdf0 with SMTP id 5b1f17b1804b1-42811d89fa6mr377505e9.10.1722009738967; Fri, 26 Jul 2024 09:02:18 -0700 (PDT) X-Google-Smtp-Source: AGHT+IEvlQVmYtYSHV2w4oWaVeN6nu2eNw75aLgomatOHw1+wGrnRlzhOnJdwzl4yuZzH8UMhx/1yQ== X-Received: by 2002:a05:600c:4443:b0:426:62df:bdf0 with SMTP id 5b1f17b1804b1-42811d89fa6mr377245e9.10.1722009738509; Fri, 26 Jul 2024 09:02:18 -0700 (PDT) Received: from ?IPV6:2003:cb:c713:a600:7ca0:23b3:d48a:97c7? (p200300cbc713a6007ca023b3d48a97c7.dip0.t-ipconnect.de. [2003:cb:c713:a600:7ca0:23b3:d48a:97c7]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4280573f935sm85232985e9.14.2024.07.26.09.02.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 26 Jul 2024 09:02:18 -0700 (PDT) Message-ID: Date: Fri, 26 Jul 2024 18:02:17 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 1/2] mm: let pte_lockptr() consume a pte_t pointer To: Peter Xu Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Muchun Song , Oscar Salvador References: <20240725183955.2268884-1-david@redhat.com> <20240725183955.2268884-2-david@redhat.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-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: p7jm6bfzuoeguuh3s7jaeuwhsyenpto1 X-Rspamd-Queue-Id: 7A71210002C X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1722009742-850821 X-HE-Meta: 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 OkufwEIj M/xjqs+DiLT/UxlhxY4O71c8wKmKMqFBnGZFA5gGXd7d60sBqudN4FTzmZEEi6aYsOiKhDhw9sMMO9js+OwShaRCOdbh4YeHCbyIXrFI83xlqNLdATxotMtFgNJVmkNtoJGURRXP+up5McIB+ksNFIRx1SpPvOzjrrd6b8n8l8YO3MiTgiiuYYt6dIqhiqcz0B9dSFLDHBvHOFKVV7lksKz/APzkH6bXBqhxtRaLJvfKTqFQZmNk91Zs+/CzcYJT/ePzjnhk2BJl+IGDatNwDFeUxWWnjdvoDR4kFoPgmQI8EvjD44mkExGqwKdPg3cXi0KyVXC5jB+FWraXE3/2CFuu/LPznJCtMfVRr4uFm5F5qwxc08wg/lOe/jlLRAjctpc3VZNi1Z62fSfCEDrBst0MBaBcSHeIyGl77 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 26.07.24 17:36, Peter Xu wrote: > On Thu, Jul 25, 2024 at 08:39:54PM +0200, David Hildenbrand wrote: >> pte_lockptr() is the only *_lockptr() function that doesn't consume >> what would be expected: it consumes a pmd_t pointer instead of a pte_t >> pointer. >> >> Let's change that. The two callers in pgtable-generic.c are easily >> adjusted. Adjust khugepaged.c:retract_page_tables() to simply do a >> pte_offset_map_nolock() to obtain the lock, even though we won't actually >> be traversing the page table. >> >> This makes the code more similar to the other variants and avoids other >> hacks to make the new pte_lockptr() version happy. pte_lockptr() users >> reside now only in pgtable-generic.c. >> >> Maybe, using pte_offset_map_nolock() is the right thing to do because >> the PTE table could have been removed in the meantime? At least it sounds >> more future proof if we ever have other means of page table reclaim. > > I think it can't change, because anyone who wants to race against this > should try to take the pmd lock first (which was held already)? That doesn't explain why it is safe for us to assume that after we took the PMD lock that the PMD actually still points at a completely empty page table. Likely it currently works by accident, because we only have a single such user that makes this assumption. It might certainly be a different once we asynchronously reclaim page tables. But yes, the PMD cannot get modified while we hold the PMD lock, otherwise we'd be in trouble > > I wonder an open coded "ptlock_ptr(page_ptdesc(pmd_page(*pmd)))" would be > nicer here, but only if my understanding is correct. I really don't like open-coding that. Fortunately we were able to limit the use of ptlock_ptr to a single user outside of arch/x86/xen/mmu_pv.c so far. -- Cheers, David / dhildenb