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(p200300d82f239c00d1f6f7fe8f147e34.dip0.t-ipconnect.de. [2003:d8:2f23:9c00:d1f6:f7fe:8f14:7e34]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3e752238832sm1808267f8f.31.2025.09.09.02.26.22 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 09 Sep 2025 02:26:24 -0700 (PDT) Message-ID: Date: Tue, 9 Sep 2025 11:26:21 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 06/16] mm: introduce the f_op->mmap_complete, mmap_abort hooks To: Lorenzo Stoakes Cc: Andrew Morton , Jonathan Corbet , Matthew Wilcox , Guo Ren , Thomas Bogendoerfer , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , "David S . Miller" , Andreas Larsson , Arnd Bergmann , Greg Kroah-Hartman , Dan Williams , Vishal Verma , Dave Jiang , Nicolas Pitre , Muchun Song , Oscar Salvador , Konstantin Komarov , Baoquan He , Vivek Goyal , Dave Young , Tony Luck , Reinette Chatre , Dave Martin , James Morse , Alexander Viro , Christian Brauner , Jan Kara , "Liam R . Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Hugh Dickins , Baolin Wang , Uladzislau Rezki , Dmitry Vyukov , Andrey Konovalov , Jann Horn , Pedro Falcato , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-csky@vger.kernel.org, linux-mips@vger.kernel.org, linux-s390@vger.kernel.org, sparclinux@vger.kernel.org, nvdimm@lists.linux.dev, linux-cxl@vger.kernel.org, linux-mm@kvack.org, ntfs3@lists.linux.dev, kexec@lists.infradead.org, kasan-dev@googlegroups.com, Jason Gunthorpe References: 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: aGYaWaPOQHE9LyiD_yQiQ5k9smm7-90JcZzPHE1DtNs_1757409986 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: xtwk3ctygcxb18sup96ejr1sy9pdzuun X-Rspam-User: X-Rspamd-Queue-Id: 5CA8FA0002 X-Rspamd-Server: rspam10 X-HE-Tag: 1757409989-715161 X-HE-Meta: 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 K2sD53zP 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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 09.09.25 11:13, Lorenzo Stoakes wrote: > On Mon, Sep 08, 2025 at 05:27:37PM +0200, David Hildenbrand wrote: >> On 08.09.25 13:10, Lorenzo Stoakes wrote: >>> We have introduced the f_op->mmap_prepare hook to allow for setting up a >>> VMA far earlier in the process of mapping memory, reducing problematic >>> error handling paths, but this does not provide what all >>> drivers/filesystems need. >>> >>> In order to supply this, and to be able to move forward with removing >>> f_op->mmap altogether, introduce f_op->mmap_complete. >>> >>> This hook is called once the VMA is fully mapped and everything is done, >>> however with the mmap write lock and VMA write locks held. >>> >>> The hook is then provided with a fully initialised VMA which it can do what >>> it needs with, though the mmap and VMA write locks must remain held >>> throughout. >>> >>> It is not intended that the VMA be modified at this point, attempts to do >>> so will end in tears. >>> >>> This allows for operations such as pre-population typically via a remap, or >>> really anything that requires access to the VMA once initialised. >>> >>> In addition, a caller may need to take a lock in mmap_prepare, when it is >>> possible to modify the VMA, and release it on mmap_complete. In order to >>> handle errors which may arise between the two operations, f_op->mmap_abort >>> is provided. >>> >>> This hook should be used to drop any lock and clean up anything before the >>> VMA mapping operation is aborted. After this point the VMA will not be >>> added to any mapping and will not exist. >>> >>> We also add a new mmap_context field to the vm_area_desc type which can be >>> used to pass information pertinent to any locks which are held or any state >>> which is required for mmap_complete, abort to operate correctly. >>> >>> We also update the compatibility layer for nested filesystems which >>> currently still only specify an f_op->mmap() handler so that it correctly >>> invokes f_op->mmap_complete as necessary (note that no error can occur >>> between mmap_prepare and mmap_complete so mmap_abort will never be called >>> in this case). >>> >>> Also update the VMA tests to account for the changes. >>> >>> Signed-off-by: Lorenzo Stoakes >>> --- >>> include/linux/fs.h | 4 ++ >>> include/linux/mm_types.h | 5 ++ >>> mm/util.c | 18 +++++-- >>> mm/vma.c | 82 ++++++++++++++++++++++++++++++-- >>> tools/testing/vma/vma_internal.h | 31 ++++++++++-- >>> 5 files changed, 129 insertions(+), 11 deletions(-) >>> >>> diff --git a/include/linux/fs.h b/include/linux/fs.h >>> index 594bd4d0521e..bb432924993a 100644 >>> --- a/include/linux/fs.h >>> +++ b/include/linux/fs.h >>> @@ -2195,6 +2195,10 @@ struct file_operations { >>> int (*uring_cmd_iopoll)(struct io_uring_cmd *, struct io_comp_batch *, >>> unsigned int poll_flags); >>> int (*mmap_prepare)(struct vm_area_desc *); >>> + int (*mmap_complete)(struct file *, struct vm_area_struct *, >>> + const void *context); >>> + void (*mmap_abort)(const struct file *, const void *vm_private_data, >>> + const void *context); >> >> Do we have a description somewhere what these things do, when they are >> called, and what a driver may be allowed to do with a VMA? > > Yeah there's a doc patch that follows this. Yeah, spotted that afterwards. > >> >> In particular, the mmap_complete() looks like another candidate for letting >> a driver just go crazy on the vma? :) > > Well there's only so much we can do. In an ideal world we'd treat VMAs as > entirely internal data structures and pass some sort of opaque thing around, but > we have to keep things real here :) Right, we'd pass something around that cannot be easily abused (like modifying random vma flags in mmap_complete). So I was wondering if most operations that driver would perform during the mmap_complete() could be be abstracted, and only those then be called with whatever opaque thing we return here. But I have no feeling about what crazy things a driver might do. Just calling remap_pfn_range() would be easy, for example, and we could abstract that. -- Cheers David / dhildenb