From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2B1A618D656 for ; Tue, 6 May 2025 14:34:09 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746542051; cv=none; b=fPBqqDZROntP4XT9ivKAONjGVt6SZDiaNX4h1aZQK6g4dmcn/jjabR4tHIH4zLI4S5dFTxwlWkicGvmxoysrKU5+NnqHl+DL3xh9fEN6vnEo4g2ZXppPcj1ydTVNBhCTOR1LlOZuMdlxA/XeXuMdPugzAWFxnhcjX3Xkh3QP3ck= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746542051; c=relaxed/simple; bh=kkFk/0AGhto/RyNrBsPnwKy+9ZIcCRZfLTqarJRbPaA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Mqb/yko8z6dpK02MZzDBoTOl5obxG9ZIAeLLGohIlDcUq93i7Q7oTF5fMqB4rfsTtmp0qQGi0TNR9QkLhEu/Cpp7ZOs4dFn+wRFX6MeRnYKWWqSfgzCZQnl2M2XWcyKfxCxJQQoLFN3NXrgMPAXiDahOIubSQAiSBUBkdhhcW6c= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=Ia69dSt0; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Ia69dSt0" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1746542048; 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=zSYTzLzA4I8JDg4pBsPS0ZO1xAUoaORmUFU9cepMeAE=; b=Ia69dSt008n8RYfVGfkicPAHCzoK95SENX1X3UiSHoGr42wz8aJRMzfsRmZ/03hmkek/u9 lyyuMoo6aAE+TteJNczGn3sAXsf2OyUkL5w5ZteD/dBgjv4O1AbsaMgjLxEFQm7IXjaZb8 xCoY8nH5m5gNYeUCXYwmsYPQ/SN6fOU= Received: from mail-wr1-f72.google.com (mail-wr1-f72.google.com [209.85.221.72]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-88-A0MRuL0bOIWpyLu2VT6THA-1; Tue, 06 May 2025 10:34:07 -0400 X-MC-Unique: A0MRuL0bOIWpyLu2VT6THA-1 X-Mimecast-MFC-AGG-ID: A0MRuL0bOIWpyLu2VT6THA_1746542046 Received: by mail-wr1-f72.google.com with SMTP id ffacd0b85a97d-3912d5f6689so2748195f8f.1 for ; Tue, 06 May 2025 07:34:07 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1746542046; x=1747146846; 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=zSYTzLzA4I8JDg4pBsPS0ZO1xAUoaORmUFU9cepMeAE=; b=iwSw+JP0TyD9RqHupk3ZUuf1Uo6n/zD9pY1dczpZS7uZbkh+5CZ/Oq9BxbRt03tjEd 9VDeR0r87WheagdI2kyhD8jBEaj5dBLPt8e2RXo5ddl4p1JazjQEYOv1UF6rsMuYq57y C55Gwsg4+wUPzIzL+qDK3lPdfidcIpSYo+KAIAD/ASW2amb+KTehu/ISYa584LnH7B+2 w/TasD06zZDGKgA2GQGf5KewDnOXm0M/CVA3hqUNb5ibtzy5JpYN+wL6rnjWjYHb/rT1 GOo7GLBgYnndcN5klg1cL64wVKBqC9ZHwHU7jzbIwwav6w/KN77oJa106fBRhtw/nFhN Cv3A== X-Forwarded-Encrypted: i=1; AJvYcCXJEtoMjA9kOpx0JdxbfEigYtCTbdg9B/oepmrxYRpilqJilb0q2//Y7eVO9+lzzEn8wje3oDoQ8LthXX8=@vger.kernel.org X-Gm-Message-State: AOJu0Yzbz603oP2yQMqBkJaHo9LYWyIFxdJ5r8kIUsrjisVZS5s+3sql 8B98gGapw05bz9lRmw+KJ51TU3ejbMDwIAuGUpf8nJZoyGDYRXTEfojNxTduztNyqrdEYmFg8/W szhW3TSYooWhEgyh0MDsQWJoglAwXqdgKSVC575+dmom2s8EfrV9vk2r3IMv9mg== X-Gm-Gg: ASbGncsfRixbqJyAGGOyhX0QNFEqClI6qn0cCl6QYaDi9ZT/SO+exImDvmlSrKmXxd6 167MQajpmtAQvEa6151Z34JbhS5D1SnRpfIa0xDIt3340tOZKRBdSO6D+s7ZMaSAJZQPpGHibT6 j7HMPUC4MJoEQbke2IDKEMGZaC64oKnAycdtPvAcUZIZ5bMr+SsdojesYOYIkctzNBPnsjYxfEu Jr7VmzmlAUcjFt4k77BmnMwHvICNPWf9x6HyeB2RIae8KazGnR+B1r6uiyfDze4H32511GSP2wK IG3VXrol9xWBgqQ/eKQyQn6l8WajVK12+lm67nTiAEbgHGh6EbI= X-Received: by 2002:a05:6000:2204:b0:39c:268e:ae04 with SMTP id ffacd0b85a97d-3a09fd0d09dmr8962673f8f.0.1746542046359; Tue, 06 May 2025 07:34:06 -0700 (PDT) X-Google-Smtp-Source: AGHT+IFUJh5j9TVIQWsrv8+lQopvkfyv6q0sW1QF6jcjHqVsYskzyqmZ/uFzWwuXJfP4bPKTDBUOGA== X-Received: by 2002:a05:6000:2204:b0:39c:268e:ae04 with SMTP id ffacd0b85a97d-3a09fd0d09dmr8962630f8f.0.1746542045945; Tue, 06 May 2025 07:34:05 -0700 (PDT) Received: from ?IPV6:2a01:599:915:8911:b13f:d972:e237:7fe2? ([2a01:599:915:8911:b13f:d972:e237:7fe2]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-441b8a286b9sm170753685e9.28.2025.05.06.07.34.04 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 06 May 2025 07:34:05 -0700 (PDT) Message-ID: Date: Tue, 6 May 2025 16:34:03 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 6/7] mm: Batch around can_change_pte_writable() To: Dev Jain , akpm@linux-foundation.org Cc: ryan.roberts@arm.com, willy@infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, catalin.marinas@arm.com, will@kernel.org, Liam.Howlett@oracle.com, lorenzo.stoakes@oracle.com, vbabka@suse.cz, jannh@google.com, anshuman.khandual@arm.com, peterx@redhat.com, joey.gouly@arm.com, ioworker0@gmail.com, baohua@kernel.org, kevin.brodsky@arm.com, quic_zhenhuah@quicinc.com, christophe.leroy@csgroup.eu, yangyicong@hisilicon.com, linux-arm-kernel@lists.infradead.org, namit@vmware.com, hughd@google.com, yang@os.amperecomputing.com, ziy@nvidia.com References: <20250429052336.18912-1-dev.jain@arm.com> <20250429052336.18912-7-dev.jain@arm.com> <25dcf969-e479-4d4a-a95c-0e83706af99e@redhat.com> <9a770aec-a020-4199-a53e-eddda657999d@redhat.com> <0857761c-bb4c-4ea5-a96a-90d555673527@arm.com> From: David Hildenbrand Content-Language: en-US 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: <0857761c-bb4c-4ea5-a96a-90d555673527@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 06.05.25 11:16, Dev Jain wrote: > > > On 29/04/25 2:57 pm, David Hildenbrand wrote: >> On 29.04.25 11:19, David Hildenbrand wrote: >>> >>>>    #include "internal.h" >>>> -bool can_change_pte_writable(struct vm_area_struct *vma, unsigned >>>> long addr, >>>> -                 pte_t pte) >>>> +bool can_change_ptes_writable(struct vm_area_struct *vma, unsigned >>>> long addr, >>>> +                  pte_t pte, struct folio *folio, unsigned int nr) >>>>    { >>>>        struct page *page; >>>> @@ -67,8 +67,9 @@ bool can_change_pte_writable(struct vm_area_struct >>>> *vma, unsigned long addr, >>>>             * write-fault handler similarly would map them writable >>>> without >>>>             * any additional checks while holding the PT lock. >>>>             */ >>>> -        page = vm_normal_page(vma, addr, pte); >>>> -        return page && PageAnon(page) && PageAnonExclusive(page); >>>> +        if (!folio) >>>> +            folio = vm_normal_folio(vma, addr, pte); >>>> +        return folio_test_anon(folio) && ! >>>> folio_maybe_mapped_shared(folio); >>> >>> Oh no, now I spot it. That is horribly wrong. >>> >>> Please understand first what you are doing. >> >> Also, would expect that the cow.c selftest would catch that: >> >> "vmsplice() + unmap in child with mprotect() optimization" >> >> After fork() we have a R/O PTE in the parent. Our child then uses >> vmsplice() and unmaps the R/O PTE, meaning it is only left mapped by the >> parent. >> >> ret = mprotect(mem, size, PROT_READ); >> ret |= mprotect(mem, size, PROT_READ|PROT_WRITE); >> >> should turn the PTE writable, although it shouldn't. >> >> If that test case does not detect the issue you're introducing, we >> should look into adding a test case that detects it. >> > > Hi David, I am afraid I don't understand my mistake :( PageAnon(page) > boils down to folio_test_anon(folio). Next we want to determine whether > the page underlying a PTE is mapped exclusively or not. No. :) There is your mistake. We need to know if this folio page is *exclusive* not if the folio is *mapped exclusively*. I know, it's confusing, but that's an important distinction. You really have to test all PAE bits. I recently sent a mail on how we could remove PAE and encode it in the PTE value itself (W || (!W +dirty)), which would mean that we could batch more easily. For the time being, we have to stick with what we have. -- Cheers, David / dhildenb