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Howlett" , James Houghton , Mike Rapoport , Lorenzo Stoakes , Axel Rasmussen References: <20250620190342.1780170-1-peterx@redhat.com> <20250620190342.1780170-2-peterx@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: <20250620190342.1780170-2-peterx@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: Ey6vCP2cHIPWfr87thkQuG8xIaTIhVPOyjJIN1UTnxY_1750667137 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 28C09100003 X-Stat-Signature: fsq61r337f4t6wo6qurzae1dgt8rcdy1 X-Rspam-User: X-HE-Tag: 1750667140-59553 X-HE-Meta: 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 8LYxI7bg 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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 20.06.25 21:03, Peter Xu wrote: Hi Peter, > Introduce a generic userfaultfd API for vm_operations_struct, so that one > vma, especially when as a module, can support userfaults without modifying The sentence is confusing ("vma ... as a module"). Did you mean something like ".. so that a vma that is backed by a special-purpose in-memory filesystem like shmem or hugetlb can support userfaultfd without modifying the uffd core; this is required when the in-memory filesystem is built as a module." > the core files. More importantly, when the module can be compiled out of > the kernel. > > So, instead of having core mm referencing modules that may not ever exist, > we need to have modules opt-in on core mm hooks instead. > > After this API applied, if a module wants to support userfaultfd, the > module should only need to touch its own file and properly define > vm_uffd_ops, instead of changing anything in core mm. Talking about modules that much is a bit confusing. I think this is more about cleanly supporting in-memory filesystems, without the need to special-case each and every one of them; can be viewed a cleanup independent of the module requirement from guest_memfd. > > Note that such API will not work for anonymous. Core mm will process > anonymous memory separately for userfault operations like before. > > This patch only introduces the API alone so that we can start to move > existing users over but without breaking them. > > Currently the uffd_copy() API is almost designed to be the simplistic with > minimum mm changes to move over to the API. > Is there a way to move part of the actual implementation (how this is all wired up) from patch #4 into this patch, to then only remove the old shmem/hugetlb hooks (that are effectively unused) in patch #4? -- Cheers, David / dhildenb