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([2a01:599:904:96e0:a245:aa9f:6c57:eb41]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38c5c1b5492sm1389915f8f.73.2025.01.30.01.24.37 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 30 Jan 2025 01:24:38 -0800 (PST) Message-ID: Date: Thu, 30 Jan 2025 10:24:37 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 04/12] mm/rmap: implement make_device_exclusive() using folio_walk instead of rmap walk From: David Hildenbrand To: Alistair Popple Cc: linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-mm@kvack.org, nouveau@lists.freedesktop.org, Andrew Morton , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , Jonathan Corbet , Alex Shi , Yanteng Si , Karol Herbst , Lyude Paul , Danilo Krummrich , David Airlie , Simona Vetter , "Liam R. Howlett" , Lorenzo Stoakes , Vlastimil Babka , Jann Horn , Pasha Tatashin , Peter Xu , Jason Gunthorpe References: <20250129115411.2077152-1-david@redhat.com> <20250129115411.2077152-5-david@redhat.com> <7tzcpx23vufmp5cxutnzhjgdj7kwqrw5drwochpv5ern7zknhj@h2s6y2qjbr3f> <180e9c2f-51fe-44ba-ac68-5aa7b7918ab0@redhat.com> 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: <180e9c2f-51fe-44ba-ac68-5aa7b7918ab0@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: Js1hn0Es-26ZX2AS7JfgMPPPAOG5xgZEjl8LtZMH7lY_1738229080 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: awcwtpy6wja898fmnx3zcz8r6jsdzg4d X-Rspamd-Queue-Id: 8C5A340006 X-Rspam-User: X-Rspamd-Server: rspam06 X-HE-Tag: 1738229083-619467 X-HE-Meta: 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 FvUS+BZR 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000002, 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 30.01.25 10:01, David Hildenbrand wrote: > On 30.01.25 07:11, Alistair Popple wrote: >> On Wed, Jan 29, 2025 at 12:54:02PM +0100, David Hildenbrand wrote: >>> We require a writable PTE and only support anonymous folio: we can only >>> have exactly one PTE pointing at that page, which we can just lookup >>> using a folio walk, avoiding the rmap walk and the anon VMA lock. >>> >>> So let's stop doing an rmap walk and perform a folio walk instead, so we >>> can easily just modify a single PTE and avoid relying on rmap/mapcounts. >>> >>> We now effectively work on a single PTE instead of multiple PTEs of >>> a large folio, allowing for conversion of individual PTEs from >>> non-exclusive to device-exclusive -- note that the other way always >>> worked on single PTEs. >>> >>> We can drop the MMU_NOTIFY_EXCLUSIVE MMU notifier call and document why >>> that is not required: GUP will already take care of the >>> MMU_NOTIFY_EXCLUSIVE call if required (there is already a device-exclusive >>> entry) when not finding a present PTE and having to trigger a fault and >>> ending up in remove_device_exclusive_entry(). >> >> I will have to look at this a bit more closely tomorrow but this doesn't seem >> right to me. We may be transitioning from a present PTE (ie. a writable >> anonymous mapping) to a non-present PTE (ie. a device-exclusive entry) and >> therefore any secondary processors (eg. other GPUs, iommus, etc.) will need to >> update their copies of the PTE. So I think the notifier call is needed. > > Then it is all very confusing: > > "MMU_NOTIFY_EXCLUSIVE: to signal a device driver that the device will no > longer have exclusive access to the page." So the second sentence actually describes the other condition. Likely we should make that clearer: --- a/include/linux/mmu_notifier.h +++ b/include/linux/mmu_notifier.h @@ -43,10 +43,11 @@ struct mmu_interval_notifier; * a device driver to possibly ignore the invalidation if the * owner field matches the driver's device private pgmap owner. * - * @MMU_NOTIFY_EXCLUSIVE: to signal a device driver that the device will no - * longer have exclusive access to the page. When sent during creation of an - * exclusive range the owner will be initialised to the value provided by the - * caller of make_device_exclusive(), otherwise the owner will be NULL. + * @MMU_NOTIFY_EXCLUSIVE: (1) to signal a device driver that the device will no + * longer have exclusive access to the page; and (2) to signal that a page will + * be made exclusive to a device. During (1), the owner will be NULL, during + * (2), the owner will be initialised to the value provided by the caller of + * make_device_exclusive(). */ enum mmu_notifier_event { MMU_NOTIFY_UNMAP = 0, -- Cheers, David / dhildenb