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X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 06 Jun 2022 13:56:18.7749 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: e9948f6f-224a-4e74-488b-08da47c454e2 X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[12.22.5.234];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: BN8NAM11FT051.eop-nam11.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM4PR12MB5279 X-Stat-Signature: 9c8fdjzuttpjs5fzs6zzp96a1pnxx93b X-Rspam-User: Authentication-Results: imf03.hostedemail.com; dkim=pass header.d=Nvidia.com header.s=selector2 header.b=EwKIaDk4; dmarc=pass (policy=reject) header.from=nvidia.com; spf=none (imf03.hostedemail.com: domain of apopple@nvidia.com has no SPF policy when checking 40.107.92.46) smtp.mailfrom=apopple@nvidia.com X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 0CCCA20055 X-HE-Tag: 1654523764-246494 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: On Monday, 6 June 2022 10:27:20 PM AEST Bharat Kumar Gogada wrote: > Hi All, > > In 5.4 kernel hmm_range structure has pfn_shift parameter. > This parameter is removed in the latest kernel. > > Can any one help me understand usage of this parameter ? I think originally it was intended to help hmm_range_fault() format PFNs into some kind of HW specific value, but it turned out not to be very useful - see 2733ea144dcc ("2733ea144dcce789de20988c1056e228a07b1bff") for more background. I think just setting it to PAGE_SHIFT would be fine. > In 5.4 kernel, if this parameter set to PAGE_SHIFT, does it mean HMM framework > expects user buffers to be 4K aligned, i.e which are allocated via mmap/ aligned_alloc ? It doesn't matter what the pfn_shift parameter is set to as HMM just copies (and reformats) CPU page tables so minimum alignment would be PAGE_SIZE (ie. generally 4K). HMM doesn't add any extra alignment constraints. > Does HMM have any alignment requirements in 5.4 or current kernel ? Will it work > with buffers allocated via malloc ? Yes. It should work with any normal page with present PTEs although I haven't personally tested it with v5.4 in a long time. There's been a number of changes in this area so I'd recommend trying to use a more recent kernel if possible. - Alistair > Regards, > bharat > > > > >