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(p200300d82f4555008267647f4209dedd.dip0.t-ipconnect.de. [2003:d8:2f45:5500:8267:647f:4209:dedd]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-442cd3af15bsm66971035e9.30.2025.05.09.03.00.39 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 09 May 2025 03:00:40 -0700 (PDT) Message-ID: <2204037e-f0bd-4059-b32a-d0970d96cea3@redhat.com> Date: Fri, 9 May 2025 12:00:38 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/3] mm: introduce new .mmap_prepare() file callback To: Lorenzo Stoakes , Andrew Morton Cc: "Liam R . Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jann Horn , Pedro Falcato , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Alexander Viro , Christian Brauner , Jan Kara , Matthew Wilcox References: From: David Hildenbrand Content-Language: en-US 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: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 07.05.25 13:03, Lorenzo Stoakes wrote: > Provide a means by which drivers can specify which fields of those > permitted to be changed should be altered to prior to mmap()'ing a > range (which may either result from a merge or from mapping an entirely new > VMA). > > Doing so is substantially safer than the existing .mmap() calback which > provides unrestricted access to the part-constructed VMA and permits > drivers and file systems to do 'creative' things which makes it hard to > reason about the state of the VMA after the function returns. > > The existing .mmap() callback's freedom has caused a great deal of issues, > especially in error handling, as unwinding the mmap() state has proven to > be non-trivial and caused significant issues in the past, for instance > those addressed in commit 5de195060b2e ("mm: resolve faulty mmap_region() > error path behaviour"). > > It also necessitates a second attempt at merge once the .mmap() callback > has completed, which has caused issues in the past, is awkward, adds > overhead and is difficult to reason about. > > The .mmap_prepare() callback eliminates this requirement, as we can update > fields prior to even attempting the first merge. It is safer, as we heavily > restrict what can actually be modified, and being invoked very early in the > mmap() process, error handling can be performed safely with very little > unwinding of state required. > > The .mmap_prepare() and deprecated .mmap() callbacks are mutually > exclusive, so we permit only one to be invoked at a time. > > Update vma userland test stubs to account for changes. > In general, looks very good to me. Some comments, especially regarding suboptimal code duplciation with the stubs. (unless I am missing fine details :) ) > Signed-off-by: Lorenzo Stoakes > --- > include/linux/fs.h | 38 +++++++++++++++ > include/linux/mm_types.h | 24 ++++++++++ > mm/memory.c | 3 +- > mm/mmap.c | 2 +- > mm/vma.c | 70 +++++++++++++++++++++++++++- > tools/testing/vma/vma_internal.h | 79 ++++++++++++++++++++++++++++++-- > 6 files changed, 208 insertions(+), 8 deletions(-) > > diff --git a/include/linux/fs.h b/include/linux/fs.h > index 016b0fe1536e..d6c5a703a215 100644 > --- a/include/linux/fs.h > +++ b/include/linux/fs.h > @@ -2169,6 +2169,7 @@ struct file_operations { > int (*uring_cmd)(struct io_uring_cmd *ioucmd, unsigned int issue_flags); > int (*uring_cmd_iopoll)(struct io_uring_cmd *, struct io_comp_batch *, > unsigned int poll_flags); > + int (*mmap_prepare)(struct vm_area_desc *); > } __randomize_layout; > > /* Supports async buffered reads */ > @@ -2238,11 +2239,48 @@ struct inode_operations { > struct offset_ctx *(*get_offset_ctx)(struct inode *inode); > } ____cacheline_aligned; > > +static inline bool file_has_deprecated_mmap_hook(struct file *file) > +{ > + return file->f_op->mmap; > +} > + > +static inline bool file_has_mmap_prepare_hook(struct file *file) > +{ > + return file->f_op->mmap_prepare; > +} I am usually not a fan of such dummy helper functions .. I mean, how far do we go? file_has_f_op() file_is_non_null() ... Or is this required for some stubbing regarding vma tests? But even the stubs below confuse me a bit, because they do exactly the same thing :( :) > + > +/* Did the driver provide valid mmap hook configuration? */ > +static inline bool file_has_valid_mmap_hooks(struct file *file) > +{ > + bool has_mmap = file_has_deprecated_mmap_hook(file); > + bool has_mmap_prepare = file_has_mmap_prepare_hook(file); > + > + /* Hooks are mutually exclusive. */ > + if (has_mmap && has_mmap_prepare) Should this be WARN_ON_ONCE() ? > + return false; > + > + /* But at least one must be specified. */ > + if (!has_mmap && !has_mmap_prepare) > + return false; > + > + return true; return has_mmap || has_mmap_prepare; And I think you can drop the comment about "at least one" with that, should be quite clear from that simplified version. > +} > + > static inline int call_mmap(struct file *file, struct vm_area_struct *vma) > { > + /* If the driver specifies .mmap_prepare() this call is invalid. */ > + if (file_has_mmap_prepare_hook(file)) Should this be WARN_ON_ONCE() ? > + return -EINVAL; > + > return file->f_op->mmap(file, vma); > } > > +static inline int __call_mmap_prepare(struct file *file, > + struct vm_area_desc *desc) > +{ > + return file->f_op->mmap_prepare(desc); > +} > + [...] > struct file { > struct address_space *f_mapping; > + const struct file_operations *f_op; > }; > > #define VMA_LOCK_OFFSET 0x40000000 > @@ -1125,11 +1157,6 @@ static inline void vm_flags_clear(struct vm_area_struct *vma, > vma->__vm_flags &= ~flags; > } > > -static inline int call_mmap(struct file *, struct vm_area_struct *) > -{ > - return 0; > -} > - > static inline int shmem_zero_setup(struct vm_area_struct *) > { > return 0; > @@ -1405,4 +1432,46 @@ static inline void free_anon_vma_name(struct vm_area_struct *vma) > (void)vma; > } > > +static inline bool file_has_deprecated_mmap_hook(struct file *file) > +{ > + return file->f_op->mmap; > +} > + > +static inline bool file_has_mmap_prepare_hook(struct file *file) > +{ > + return file->f_op->mmap_prepare; > +} > +> +/* Did the driver provide valid mmap hook configuration? */ > +static inline bool file_has_valid_mmap_hooks(struct file *file) > +{ > + bool has_mmap = file_has_deprecated_mmap_hook(file); > + bool has_mmap_prepare = file_has_mmap_prepare_hook(file); > + > + /* Hooks are mutually exclusive. */ > + if (has_mmap && has_mmap_prepare) > + return false; > +> + /* But at least one must be specified. */ > + if (!has_mmap && !has_mmap_prepare) > + return false; > + > + return true;> +} > + > +static inline int call_mmap(struct file *file, struct vm_area_struct *vma) > +{ > + /* If the driver specifies .mmap_prepare() this call is invalid. */ > + if (file_has_mmap_prepare_hook(file)) > + return -EINVAL;> + > + return file->f_op->mmap(file, vma); > +} > + > +static inline int __call_mmap_prepare(struct file *file, > + struct vm_area_desc *desc) > +{ > + return file->f_op->mmap_prepare(desc); > +} Hm, is there a way avoid a copy of the exact same code from fs.h, and essentially test the implementation in fs.h (-> more coverage by using less duplciated stubs?). -- Cheers, David / dhildenb