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Miller" , Andreas Larsson , Arnd Bergmann , Greg Kroah-Hartman , Dan Williams , Vishal Verma , Dave Jiang , Nicolas Pitre , Muchun Song , Oscar Salvador , David Hildenbrand , 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, iommu@lists.linux.dev, Kevin Tian , Will Deacon , Robin Murphy Subject: Re: [PATCH v3 11/13] mm: update mem char driver to use mmap_prepare Message-ID: <20250916174006.GS1086830@nvidia.com> References: <03d4fce5fd356022b5af453fc5ab702c2c3a36d6.1758031792.git.lorenzo.stoakes@oracle.com> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <03d4fce5fd356022b5af453fc5ab702c2c3a36d6.1758031792.git.lorenzo.stoakes@oracle.com> X-ClientProxiedBy: BLAPR03CA0056.namprd03.prod.outlook.com (2603:10b6:208:32d::31) To PH7PR12MB5757.namprd12.prod.outlook.com (2603:10b6:510:1d0::13) Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: PH7PR12MB5757:EE_|SN7PR12MB8130:EE_ X-MS-Office365-Filtering-Correlation-Id: 8cb764e8-ebc7-4e7b-b17a-08ddf5481478 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|366016|376014|7416014; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?W5yRxc6sKftRS/lKAeRN3CkrPIXJN+SW8mmQJ5Tvu8aVDoFTdE1nJ1T50utS?= =?us-ascii?Q?FqLCujN/0JTTOHUe99loE88Wf8SlYXK51E1uj3lWGakr6A663zUgjGuKIgcu?= =?us-ascii?Q?WP7BcIUPvT8qe6puocnBQpBmYlseuqTHnzFUwlCnfD50meFqJAPUI6BULvKm?= =?us-ascii?Q?4kwQIuVOtk+331PLrcmKoxdNQJKgRrZaMXZOyvWzaL5/uZG8/xzh3fvIobhg?= =?us-ascii?Q?7f4qEOw6fidPYGTFxzDP5NVzzbmnPnHQv2zyBEI1T2AIBTPwrEel8uAOvbBL?= =?us-ascii?Q?ByYdBj+1pnUrqmEDEN8SQ3+qGWrWCA7bFU5AAw00r711m/tRT7pi8xt5kuOn?= =?us-ascii?Q?bd12S29DyTnSWnjJZntz96fEj6DVKQf495AQlNEW+Ps2chTq+kx7aE9uHVmF?= =?us-ascii?Q?omAzpYwjJPRaqWIEsiZaAuxFJbwJkWlncn4nCGsmW1kP4KRhY41gefO7Bi9s?= =?us-ascii?Q?8JN7OlcL9h6MyCC34mOhu66FYvG9iYjVFIDFeGyJaA8aM7eMIAT6OT5cCtBQ?= =?us-ascii?Q?Y0dcbXCOASHYrYFfVh4wj6S719dQeJPEpa6MoBCfUMzzr/ZI/betPVLlX0Rm?= =?us-ascii?Q?uDwcfnmwq7/5+1+4cI4YOQ0+nVrX4tU4bS1Lc/vpsh6Ffws5x4Bsh8WMI/sQ?= =?us-ascii?Q?QM2wkDOHvsC+kih5FmDUcCU1f5ZxHo5OSJ2thusOUJZMxUZV6e4NSrEjXLQF?= =?us-ascii?Q?ynYN7U38fJhqtHXQx1yNwdIjZbzgLfryYBom3bYzvOhEBQ/9BlRGPcmKdxA2?= =?us-ascii?Q?4c+wf5iDqZy/KvHmBRIBGxWodOJtYP5LTPL8bcl9cvSIh7Ke8pijle5MNQZz?= =?us-ascii?Q?ay7qPDL3f/DlSIqF7MtjdWBBfoejzlDLu2x1FcitpGy5HaqOCbO2D/wfo3QI?= =?us-ascii?Q?Y3dXPUZNqmAkHG1N1fsqParpepoxnCTy/MTu9KMxVRpBsy21NBATQK46mKXB?= =?us-ascii?Q?lyE9hPxbsdTExhXqKpui4LErVb0Z6C+grqrM9j5eXaYnqe+hhpmnZnkkJJ5+?= =?us-ascii?Q?ng3GISP3s8Ntm8fWkWjxcSS9+zv97PEwM0t124ieZMNT3zLcMXYQSy76ioRZ?= =?us-ascii?Q?iitxYAIlIn2re729TkCaExqW7xdD7vKOiEsDYTrO/W55mcYUFElhhOzb0dJ2?= =?us-ascii?Q?0hcrkDjOSGpwT2pJEdizDlBBuCx2eCYCF4znDb4cQYtnm4mRxbI34QENN+De?= =?us-ascii?Q?nryxiX1KqRmQZx8jtqDax7JKIjskY3u9Jge76kDg+FWWhhfPSxDsczsPH07V?= =?us-ascii?Q?PrsT6Zq07xY+FeGic3XXiKwCwTbW1hkqRi59bviVERdnk+g9UIcGBzuDo9Hw?= =?us-ascii?Q?3QtVjariEs6RSX6d2VywksmJi6Xd4z6rm7XzBA5b2cMJLmhdwvnwxhiGtqF1?= =?us-ascii?Q?OR5TDDBqL+4TDwUabSmXtDEnliP4PU0oc+6EbfKWOkAn8m5LCWc/Q6M+hsfd?= =?us-ascii?Q?nRS0VzUc4PNrDlp9Twz9Fz0BfnXQi3eC9G2tuQm8DTgS0tI15A8ZjA7OSUWJ?= =?us-ascii?Q?O5QCP0VEnWINf7Jz5RhoS0OeMUcYYBcdfz/OgypEkrpB7MfZPiyivfShriNc?= =?us-ascii?Q?fDdiz86PeRO0Za1m3BhHOTa6VP3wGlAfu+Ybnesq?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 8cb764e8-ebc7-4e7b-b17a-08ddf5481478 X-MS-Exchange-CrossTenant-AuthSource: PH7PR12MB5757.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 16 Sep 2025 17:40:08.8596 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: O8/N3WC2EpvfaG+bbRE0ALwfOCd4/b/zgyU8mLqy+0J2yiVIunz/zXcbVY38WBXF X-MS-Exchange-Transport-CrossTenantHeadersStamped: SN7PR12MB8130 On Tue, Sep 16, 2025 at 03:11:57PM +0100, Lorenzo Stoakes wrote: > Update the mem char driver (backing /dev/mem and /dev/zero) to use > f_op->mmap_prepare hook rather than the deprecated f_op->mmap. > > The /dev/zero implementation has a very unique and rather concerning > characteristic in that it converts MAP_PRIVATE mmap() mappings anonymous > when they are, in fact, not. > > The new f_op->mmap_prepare() can support this, but rather than introducing > a helper function to perform this hack (and risk introducing other users), > simply set desc->vm_op to NULL here and add a comment describing what's > going on. > > We also introduce shmem_zero_setup_desc() to allow for the shared mapping > case via an f_op->mmap_prepare() hook, and generalise the code between > this and shmem_zero_setup(). > > We also use the desc->action_error_hook to filter the remap error to > -EAGAIN to keep behaviour consistent. Hurm, in practice this converts reserve_pfn_range()/etc conflicts into from EINVAL into EAGAIN and converts all the unlikely OOM ENOMEM failures to EAGAIN. Seems wrong/unnecessary to me, I wouldn't have preserved it. But oh well Reviewed-by: Jason Gunthorpe > diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h > index 0e47465ef0fd..5b368f9549d6 100644 > --- a/include/linux/shmem_fs.h > +++ b/include/linux/shmem_fs.h This little bit should probably be its own patch "Add shmem_zero_setup_desc()", and I wonder if the caller from vma.c can call the desc version now? Too bad the usage in ppc is such an adventure through sysfs :\ But the code looks fine Jason