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[80.187.83.110]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-46fa3acf0c1sm18566445e9.9.2025.10.07.09.14.02 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 07 Oct 2025 09:14:04 -0700 (PDT) Message-ID: <9089d994-262f-4941-8bed-f3c6ee05a769@redhat.com> Date: Tue, 7 Oct 2025 18:14:01 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 1/4] mm: Introduce vm_uffd_ops API To: "Liam R. Howlett" , Peter Xu , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Axel Rasmussen , Vlastimil Babka , James Houghton , Nikita Kalyazin , Lorenzo Stoakes , Ujwal Kundur , Mike Rapoport , Andrew Morton , Andrea Arcangeli , Michal Hocko , Muchun Song , Oscar Salvador , Hugh Dickins , Suren Baghdasaryan References: <43d78ba7-8829-4a19-bdf3-d192a62cdac4@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 ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZoEEwEIAEQCGwMCF4ACGQEFCwkIBwICIgIG FQoJCAsCBBYCAwECHgcWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaJzangUJJlgIpAAKCRBN 3hD3AP+DWhAxD/9wcL0A+2rtaAmutaKTfxhTP0b4AAp1r/eLxjrbfbCCmh4pqzBhmSX/4z11 opn2KqcOsueRF1t2ENLOWzQu3Roiny2HOU7DajqB4dm1BVMaXQya5ae2ghzlJN9SIoopTWlR 0Af3hPj5E2PYvQhlcqeoehKlBo9rROJv/rjmr2x0yOM8qeTroH/ZzNlCtJ56AsE6Tvl+r7cW 3x7/Jq5WvWeudKrhFh7/yQ7eRvHCjd9bBrZTlgAfiHmX9AnCCPRPpNGNedV9Yty2Jnxhfmbv Pw37LA/jef8zlCDyUh2KCU1xVEOWqg15o1RtTyGV1nXV2O/mfuQJud5vIgzBvHhypc3p6VZJ lEf8YmT+Ol5P7SfCs5/uGdWUYQEMqOlg6w9R4Pe8d+mk8KGvfE9/zTwGg0nRgKqlQXrWRERv cuEwQbridlPAoQHrFWtwpgYMXx2TaZ3sihcIPo9uU5eBs0rf4mOERY75SK+Ekayv2ucTfjxr Kf014py2aoRJHuvy85ee/zIyLmve5hngZTTe3Wg3TInT9UTFzTPhItam6dZ1xqdTGHZYGU0O otRHcwLGt470grdiob6PfVTXoHlBvkWRadMhSuG4RORCDpq89vu5QralFNIf3EysNohoFy2A LYg2/D53xbU/aa4DDzBb5b1Rkg/udO1gZocVQWrDh6I2K3+cCs7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: CMRkD_MtkhbX6VfC_JcLwSJNK37fqmy-dILaYL0VLBk_1759853645 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 55DEE12000E X-Rspamd-Server: rspam11 X-Rspam-User: X-Stat-Signature: 4wjrhcf5j9hrkifp3zz83s63m3ufgaaf X-HE-Tag: 1759853648-538739 X-HE-Meta: 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 Ho1FD5r9 1QumryInlFViYyDTiIKVJrQTQlpDTqt6xE5hfXysdKbEUKrIqNQdNNwwezuN5S8fEPZ5/uAAxebMDjGsfeHEA8dWUGggTQ6d/4mhcyZWM7akMd/FSqG9f8Avb6PKoG7qxbbLlY446PNK8XvlKxHS2e3BXYXk2aAdzhn00PlFRKTeUmKZmbh+QJCpR045soCDzq0TeVTB/7iyOvpS8rY8eHqg36RuTtknCF9EnLE7Ow4R8D/EA/MrI+phKwahXfnu+w+ndrDw/hkQvQo3SpBIzntseBFjBkd/grHn3vRzWOihrv9IURceeA1g0JhZ+WazR/fQ66a95to1ADxwR6/UcCDZcbH5tviQRE/jlgkEMN+YvvKiISZeVcFQO/bnfVti0lZEK+WgOJwJ+pycCYxIa91rv4Ox48W8GfnvlIUq9ia3umdum5TFLec3bHMGSotD0f1dInpFIUUCc9/A3JlPAazeUPdbPfmNFyVwAt3BEW88hhdGbWqddICi/+g== 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: >> If so, I'd prefer that rather than introducing feature-backend flags, >> because I want to avoid introducing another different feature set to uffd. >> > > I was talking about uffd_features. I thought it was being renamed to > flags, not modes_supported. It was pretty late when I responded. > > FWIU, David was saying we don't need both of modes and ioctl listed in > the uffd_ops? Right, I would have abstracted the features to clean it up and avoid using VM_ flags in this interface. > > I was thinking that we could just put the features directly as function > pointers in the uffd_ops and check if they are NULL or not for > 'support'. > > ie: > > struct vm_uffd_ops hugetlb_uffd_ops = { > .missing = hugetlb_handle_userfault, > .write_protect = mwriteprotect_range, > .minor = hugetlb_handle_userfault_minor, > > .mfill_atomic = hugetlb_mfill_atomic_pte, > .mfill_atomic_continue = ... > .mfill_zeropage = ... > .mfill_poison = ... > .mfill_copy = NULL, /* For example */ > }; > > Then mfill_atomic_copy() becomes: > { > /* > * Maybe some setup, used for all mfill operations from > * mfill_atomic() > */ > > ... > > dst_vma = uffd_mfill_lock() > uffd_ops = vma_get_uffd_ops(vma); > if (!uffd_ops) > return false; > > if (!uffd_ops->mfill_copy) /* unlikely? */ > return false; > > return uffd_ops->mfill_copy(dst_vma,..); > } > > This way is_vm_hugetlb_page() never really needs to be used because the > function pointer already makes that distinction. > > Right now, we have checks for hugetlb through other functions that "pass > off to appropriate routine", and we end up translating the > ioctl_supports into the function call eventually, anyways. Right, it would be great to get rid of that. I recall I asked for such a cleanup in RFC (or was it v1). -- Cheers David / dhildenb