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 8E61BC6FD1F for ; Tue, 26 Mar 2024 16:30:38 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id F3CB36B0096; Tue, 26 Mar 2024 12:30:37 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id EEE206B0098; Tue, 26 Mar 2024 12:30:37 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id D65D06B0099; Tue, 26 Mar 2024 12:30:37 -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 C3E386B0096 for ; Tue, 26 Mar 2024 12:30:37 -0400 (EDT) Received: from smtpin10.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay02.hostedemail.com (Postfix) with ESMTP id 4589A120C14 for ; Tue, 26 Mar 2024 16:30:37 +0000 (UTC) X-FDA: 81939728514.10.7C6A43D Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by imf11.hostedemail.com (Postfix) with ESMTP id DD7E040011 for ; Tue, 26 Mar 2024 16:30:34 +0000 (UTC) Authentication-Results: imf11.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=fGdgGqC4; dmarc=pass (policy=none) header.from=redhat.com; spf=pass (imf11.hostedemail.com: domain of david@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=david@redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1711470635; 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=nn/mnDpTqidEVrLysEN0UnzTs/KqUQ/RCKtm5EBNTEY=; b=LboazrCwhiMyfoJudMY/3rySa331+StFubjnyv+SrXQpm9PDL1GxyO5pOR2IbHTBWWH9w3 RHa9nKyXa1uMG7y6RkrZ3gfoPRdh6f7cas5uBpIbePduKSPox1ws5F2eFJ/Vx9anYebaQc DJx7yGfx3Y6rbIk76s06/uPB55U23AQ= ARC-Authentication-Results: i=1; imf11.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=fGdgGqC4; dmarc=pass (policy=none) header.from=redhat.com; spf=pass (imf11.hostedemail.com: domain of david@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=david@redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1711470635; a=rsa-sha256; cv=none; b=uQ8fcBvGwgNW0nQpy6+RZglHrgtkzb+CC9OwOaMR8YVF61IvD9FgDg6RuPi01Vt/pCrGrU 0nwwVX0l6VN38gFVlDJbwZmkcN6k3Zgl2q35eYKJJ06Eq7cWhJQEel43o7XXqaSPyb9fra 3lWgVpI2t4EI3rIBCOuFsNKG9ZJUL+8= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1711470634; 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=nn/mnDpTqidEVrLysEN0UnzTs/KqUQ/RCKtm5EBNTEY=; b=fGdgGqC46NQgkvAihd8a+LbfNnQs9iKmoiMGTPlT1jMIL47iZH11q3atpFw9Y2cmUGqYLb yNRikloG6/vcautI8V85vJ2qyYpj02zT/t+31ZHemZmoU361KC5tYx8C7mKsS4QjYUIVMC W1gnsXFJ8PAm7H6XELFEw/9/01US57U= Received: from mail-lf1-f71.google.com (mail-lf1-f71.google.com [209.85.167.71]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-408-LTK06ZOyNDKxBX8X2sjJIw-1; Tue, 26 Mar 2024 12:30:31 -0400 X-MC-Unique: LTK06ZOyNDKxBX8X2sjJIw-1 Received: by mail-lf1-f71.google.com with SMTP id 2adb3069b0e04-5159dbd6be4so3607304e87.1 for ; Tue, 26 Mar 2024 09:30:30 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1711470629; x=1712075429; h=content-transfer-encoding:in-reply-to:organization:autocrypt:from :references:cc:to:content-language:subject:user-agent:mime-version :date:message-id:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=nn/mnDpTqidEVrLysEN0UnzTs/KqUQ/RCKtm5EBNTEY=; b=JEDxL2zaH92X3egkfL+oLWNbfs5DL7AOIKvfPbOPqzajjPt0wx6EbfLW+pxxaKCWph AypffKuY6Rv0zOF5OAcON/0LC+46E/ByJOIccGiWo9bjo0kCE7/PG2yhneRdb4qf3gTD DE8if+H9tBXzWGyNhhEjUqWa+g89pJwtC5NhJ1G9T7JoiYuOzPq6vBTbybK3bHFBWeIe zOQISy1aXoVDIve3SBISJnH1FQdOyekYJnphMaLjESWm29ETq40svV6IAdso7DOm9jGt EKN/2HvFjR3l05QMPFIoO9xQvyN3FYgWsNlQ6q7+vSsMDMWZ48F5j6FVAyThkaVLpVa1 Y6Lw== X-Forwarded-Encrypted: i=1; AJvYcCUkqW0YGy7f/KfM6X2ybGtfjWDPj9sD3RVL28lWQHVw7PCd7UZu1hwYo9ehoNrqjSEXC35D2KtW8L9un4HocK2lnoI= X-Gm-Message-State: AOJu0Yyc6qz+3G9GDbnKGK2zg1hvrCxya0t4i1k4Jo5XgFCgYQkjEkeJ zD0Eb6d2gCmcUYe2BiG2LC4xpcAQK4DVwhtIBnFrDLE5fM8CDbLfMudMK/XhLaNMpc81jFdEpuH nCuNUCh4fqyiIfoE1vQTsw20jCDcmFfou3US7U7NsbEhlbUqR X-Received: by 2002:a05:6512:608:b0:515:b0ef:2ae3 with SMTP id b8-20020a056512060800b00515b0ef2ae3mr65139lfe.39.1711470629680; Tue, 26 Mar 2024 09:30:29 -0700 (PDT) X-Google-Smtp-Source: AGHT+IEsbc5I3/mdRSiPnDEiL3mXkX65OqA74KylNSG04oG/vkcfYFpydkLdpBsHCPFkF+OzwQjfeg== X-Received: by 2002:a05:6512:608:b0:515:b0ef:2ae3 with SMTP id b8-20020a056512060800b00515b0ef2ae3mr65115lfe.39.1711470629198; Tue, 26 Mar 2024 09:30:29 -0700 (PDT) Received: from ?IPV6:2003:cb:c741:c700:3db9:94c9:28b0:34f2? (p200300cbc741c7003db994c928b034f2.dip0.t-ipconnect.de. [2003:cb:c741:c700:3db9:94c9:28b0:34f2]) by smtp.gmail.com with ESMTPSA id s8-20020a5d69c8000000b0033e206a0a7asm12501977wrw.26.2024.03.26.09.30.28 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 26 Mar 2024 09:30:28 -0700 (PDT) Message-ID: <5d80c368-7ce7-4a44-9cd7-aee3e1c9182b@redhat.com> Date: Tue, 26 Mar 2024 17:30:27 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v1 2/4] mm/gup: Use ptep_get_lockless_norecency() To: Ryan Roberts , Mark Rutland , Catalin Marinas , Will Deacon , Alexander Shishkin , Jiri Olsa , Ian Rogers , Adrian Hunter , Andrew Morton , Muchun Song Cc: linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20240215121756.2734131-1-ryan.roberts@arm.com> <20240215121756.2734131-3-ryan.roberts@arm.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: <20240215121756.2734131-3-ryan.roberts@arm.com> 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-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: DD7E040011 X-Stat-Signature: g8dwe97zmjro63maukz1dcs87e7yzann X-HE-Tag: 1711470634-847423 X-HE-Meta: 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 KNE5Ki00 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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 15.02.24 13:17, Ryan Roberts wrote: > Gup needs to read ptes locklessly, so it uses ptep_get_lockless(). > However, the returned access and dirty bits are unimportant so let's > switch over to ptep_get_lockless_norecency(). > > The wrinkle is that gup needs to check that the pte hasn't changed once > it has pinned the folio following this model: > > pte = ptep_get_lockless_norecency(ptep) > ... > if (!pte_same(pte, ptep_get_lockless(ptep))) > // RACE! > ... > > And now that pte may not contain correct access and dirty information, > the pte_same() comparison could spuriously fail. So let's introduce a > new pte_same_norecency() helper which will ignore the access and dirty > bits when doing the comparison. > > Note that previously, ptep_get() was being used for the comparison; this > is technically incorrect because the PTL is not held. I've also > converted the comparison to use the preferred pmd_same() helper instead > of doing a raw value comparison. > > As a side-effect, this new approach removes the possibility of > concurrent read/write to the page causing a spurious fast gup failure, > because the access and dirty bits are no longer used in the comparison. > > Signed-off-by: Ryan Roberts > --- [...] > #ifndef __HAVE_ARCH_PTE_UNUSED > /* > * Some architectures provide facilities to virtualization guests > diff --git a/mm/gup.c b/mm/gup.c > index df83182ec72d..0f96d0a5ec09 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -2576,7 +2576,7 @@ static int gup_pte_range(pmd_t pmd, pmd_t *pmdp, unsigned long addr, > if (!ptep) > return 0; > do { > - pte_t pte = ptep_get_lockless(ptep); > + pte_t pte = ptep_get_lockless_norecency(ptep); > struct page *page; > struct folio *folio; > > @@ -2617,8 +2617,9 @@ static int gup_pte_range(pmd_t pmd, pmd_t *pmdp, unsigned long addr, > goto pte_unmap; > } > > - if (unlikely(pmd_val(pmd) != pmd_val(*pmdp)) || > - unlikely(pte_val(pte) != pte_val(ptep_get(ptep)))) { > + if (unlikely(!pmd_same(pmd, *pmdp)) || > + unlikely(!pte_same_norecency(pte, > + ptep_get_lockless_norecency(ptep)))) { > gup_put_folio(folio, 1, flags); > goto pte_unmap; We pass the pte into pte_access_permitted(). It would be good to mention that you checked all implementations. Acked-by: David Hildenbrand -- Cheers, David / dhildenb