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[80.187.80.144]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-46e4ab0bf62sm109304255e9.9.2025.09.30.02.36.54 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 30 Sep 2025 02:36:57 -0700 (PDT) Message-ID: Date: Tue, 30 Sep 2025 11:36:53 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 1/4] mm: Introduce vm_uffd_ops API To: Peter Xu , linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: 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> 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: <20250926211650.525109-2-peterx@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: EpreA-ZLPUFhF9EJZEMfCaYlz_yYpJZYIDLDpvJHqR0_1759225018 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: hke8brdb8z648m9wu9hhpwqjzst36ggr X-Rspamd-Queue-Id: ADCCD4000A X-Rspam-User: X-Rspamd-Server: rspam03 X-HE-Tag: 1759225023-528451 X-HE-Meta: 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 C6yv2nYB 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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 26.09.25 23:16, Peter Xu wrote: > Currently, most of the userfaultfd features are implemented directly in the > core mm. It will invoke VMA specific functions whenever necessary. So far > it is fine because it almost only interacts with shmem and hugetlbfs. > > Introduce a generic userfaultfd API extension for vm_operations_struct, > so that any code that implements vm_operations_struct (including kernel > modules that can be compiled separately from the kernel core) can support > userfaults without modifying the core files. > > With this API applied, if a module wants to support userfaultfd, the > module should only need to properly define vm_uffd_ops and hook it to > vm_operations_struct, instead of changing anything in core mm. > > This API will not work for anonymous memory. Handling of userfault > operations for anonymous memory remains unchanged in core mm. > > Due to a security concern while reviewing older versions of this series > [1], uffd_copy() will be temprorarily removed. IOW, so far MISSING-capable > memory types can only be hard-coded and implemented in mm/. It would also > affect UFFDIO_COPY and UFFDIO_ZEROPAGE. Other functions should still be > able to be provided from vm_uffd_ops. > > Introduces the API only so that existing userfaultfd users can be moved > over without breaking them. > > [1] https://lore.kernel.org/all/20250627154655.2085903-1-peterx@redhat.com/ > Looks much better with the uffdio_copy stuff removed for now. > Signed-off-by: Peter Xu > --- > include/linux/mm.h | 9 +++++++++ > include/linux/userfaultfd_k.h | 37 +++++++++++++++++++++++++++++++++++ > 2 files changed, 46 insertions(+) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 6b6c6980f46c2..8afb93387e2c6 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -620,6 +620,8 @@ struct vm_fault { > */ > }; > > +struct vm_uffd_ops; > + > /* > * These are the virtual MM functions - opening of an area, closing and > * unmapping it (needed to keep files on disk up-to-date etc), pointer > @@ -705,6 +707,13 @@ struct vm_operations_struct { > struct page *(*find_normal_page)(struct vm_area_struct *vma, > unsigned long addr); > #endif /* CONFIG_FIND_NORMAL_PAGE */ > +#ifdef CONFIG_USERFAULTFD > + /* > + * Userfaultfd related ops. Modules need to define this to support > + * userfaultfd. > + */ > + const struct vm_uffd_ops *userfaultfd_ops; > +#endif > }; > > #ifdef CONFIG_NUMA_BALANCING > diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h > index c0e716aec26aa..b1949d8611238 100644 > --- a/include/linux/userfaultfd_k.h > +++ b/include/linux/userfaultfd_k.h > @@ -92,6 +92,43 @@ enum mfill_atomic_mode { > NR_MFILL_ATOMIC_MODES, > }; > > +/* VMA userfaultfd operations */ > +struct vm_uffd_ops { > + /** > + * @uffd_features: features supported in bitmask. > + * > + * When the ops is defined, the driver must set non-zero features > + * to be a subset (or all) of: VM_UFFD_MISSING|WP|MINOR. > + * > + * NOTE: VM_UFFD_MISSING is still only supported under mm/ so far. > + */ > + unsigned long uffd_features; This variable name is a bit confusing , because it's all about vma flags, not uffd features. Just reading the variable, I would rather connect it to things like UFFD_FEATURE_WP_UNPOPULATED. As currently used for VM flags, maybe you should call this unsigned long uffd_vm_flags; or sth like that. 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 > + /** > + * @uffd_ioctls: ioctls supported in bitmask. > + * > + * Userfaultfd ioctls supported by the module. Below will always > + * be supported by default whenever a module provides vm_uffd_ops: > + * > + * _UFFDIO_API, _UFFDIO_REGISTER, _UFFDIO_UNREGISTER, _UFFDIO_WAKE > + * > + * The module needs to provide all the rest optionally supported > + * ioctls. For example, when VM_UFFD_MINOR is supported, > + * _UFFDIO_CONTINUE must be supported as an ioctl. > + */ > + unsigned long uffd_ioctls; > + /** > + * uffd_get_folio: Handler to resolve UFFDIO_CONTINUE request. Just wondering if we could incorporate the "continue" / "minor" aspect into the callback name. uffd_minor_get_folio / uffd_continue_get_folio Or do you see use of that callback in the context of other uffd features? -- Cheers David / dhildenb