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[80.187.80.144]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-40fb72fb729sm26620363f8f.6.2025.10.01.07.39.56 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 01 Oct 2025 07:39:58 -0700 (PDT) Message-ID: Date: Wed, 1 Oct 2025 16:39:50 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 1/4] mm: Introduce vm_uffd_ops API To: Peter Xu Cc: 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 , "Liam R . Howlett" , Michal Hocko , Muchun Song , Oscar Salvador , Hugh Dickins , Suren Baghdasaryan References: <20250926211650.525109-1-peterx@redhat.com> <20250926211650.525109-2-peterx@redhat.com> <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: S8cwt4sntyB7DN9zdO6Ar4iqfxCnbwSrSORDLpkQWsQ_1759329600 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: 5318918001D X-Rspamd-Server: rspam05 X-Stat-Signature: wa47n9by7mmbqd9xygpyz18bt6qz7ha8 X-Rspam-User: X-HE-Tag: 1759329603-850394 X-HE-Meta: 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 0WbNBFj/ 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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 01.10.25 16:35, Peter Xu wrote: > On Wed, Oct 01, 2025 at 03:58:14PM +0200, David Hildenbrand wrote: >>>>>> I briefly wondered whether we could use actual UFFD_FEATURE_* here, but they >>>>>> are rather unsuited for this case here (e.g., different feature flags for >>>>>> hugetlb support/shmem support etc). >>>>>> >>>>>> But reading "uffd_ioctls" below, can't we derive the suitable vma flags from >>>>>> the supported ioctls? >>>>>> >>>>>> _UFFDIO_COPY | _UFDIO_ZEROPAGE -> VM_UFFD_MISSING >>>>>> _UFFDIO_WRITEPROTECT -> VM_UFFD_WP >>>>>> _UFFDIO_CONTINUE -> VM_UFFD_MINOR >>>>> >>>>> Yes we can deduce that, but it'll be unclear then when one stares at a >>>>> bunch of ioctls and cannot easily digest the modes the memory type >>>>> supports. Here, the modes should be the most straightforward way to >>>>> describe the capability of a memory type. >>>> >>>> I rather dislike the current split approach between vm-flags and ioctls. >>>> >>>> I briefly thought about abstracting it for internal purposes further and >>>> just have some internal backend ("memory type") flags. >>>> >>>> UFFD_BACKEND_FEAT_MISSING -> _UFFDIO_COPY and VM_UFFD_MISSING >>>> UFFD_BACKEND_FEAT_ZEROPAGE -> _UFDIO_ZEROPAGE >>>> UFFD_BACKEND_FEAT_WP -> _UFFDIO_WRITEPROTECT and VM_UFFD_WP >>>> UFFD_BACKEND_FEAT_MINOR -> _UFFDIO_CONTINUE and VM_UFFD_MINOR >>>> UFFD_BACKEND_FEAT_POISON -> _UFFDIO_POISON >>> >>> This layer of mapping can be helpful to some, but maybe confusing to >>> others.. who is familiar with existing userfaultfd definitions. >>> >> >> Just wondering, is this confusing to you, and if so, which part? >> >> To me it makes perfect sense and cleans up this API and not have to sets of >> flags that are somehow interlinked. > > It adds the extra layer of mapping that will only be used in vm_uffd_ops > and the helper that will consume it. Agreed, while making the API cleaner. I don't easily see what's confusing about that, though. I think it can be done with a handful of LOC and avoid having to use VM_ flags in this API. -- Cheers David / dhildenb