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V" , Mike Kravetz Subject: Re: [PATCH v3 05/12] mm/gup: Drop folio_fast_pin_allowed() in hugepd processing Message-ID: <20240322122842.GH159172@nvidia.com> References: <20240321220802.679544-1-peterx@redhat.com> <20240321220802.679544-6-peterx@redhat.com> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240321220802.679544-6-peterx@redhat.com> X-ClientProxiedBy: MN2PR08CA0022.namprd08.prod.outlook.com (2603:10b6:208:239::27) To DM6PR12MB3849.namprd12.prod.outlook.com (2603:10b6:5:1c7::26) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DM6PR12MB3849:EE_|SA0PR12MB4400:EE_ X-MS-Office365-Filtering-Correlation-Id: ab966d8d-c364-4bf1-e90a-08dc4a6b9d10 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: CPnMZoVExzZHDb9OcxiBgGLYitj5FIIiqx32x4mh44DbnWWdt/methTG85EHxb44fo5BD0JaKFBeNACN1qaSgAIXeNNkTyfKlYyzLvf2JB/WSSWZkMdHUHGy1WbANI+tlgt+r1PLPVALYEKGkAD2TdhJ4Bc+lFw75s0GO/+NbAzbI3fDUbpKksfDCaiwdJzL2jA8H/tC1HT+56NMMLb7PjaqbETQsh8yv1XZqvkWw/F/xRe2YWh6W9dZBi8MLfzCGDOEnwfQZN627bveMQflRna9LXuHBZrr9UM8HPFzMbm2ZUrl25AvHSTFWFubzFrLlon1MeRm7gGmRXvMT8CWVfz6ejwtuCuVdxnc/6iitjnXuiaZi5T18J8XfcbkAeytJRnXoyPsaenBtFFspVvhKxAW+Rc5tThWe8z63TAFkRTeXTg1uO68Zxh3ejXMvFEtT5mySiC1NR1sq3sjhMjr1g4qeMRQuu+hY7Dim8DH3r7x1kmkRTQnN1xpbNyPoPmxTxfL7HP0xQEdpsfrIW+dx8BjH6edJOEPCVEO6pWOQUU4gvydVz6FxwrG9iqloL8xq5Q8xXOtGZDDvTYJvPKL+zLTPx1rUoXLpVPsdCPfOI6DJRp8QBuItK5eCZgChc4CglHOdqd7IzhI0s63EmKFTGTgishF9KZWjk3mU/fO+AA= X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:DM6PR12MB3849.namprd12.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230031)(376005)(1800799015)(7416005)(366007);DIR:OUT;SFP:1101; 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There are > some kernel usage of hugepd (can refer to hugepd_populate_kernel() for > PPC_8XX), however those pages are not candidates for GUP. > > Commit a6e79df92e4a ("mm/gup: disallow FOLL_LONGTERM GUP-fast writing to > file-backed mappings") added a check to fail gup-fast if there's potential > risk of violating GUP over writeback file systems. That should never apply > to hugepd. Considering that hugepd is an old format (and even > software-only), there's no plan to extend hugepd into other file typed > memories that is prone to the same issue. > > Drop that check, not only because it'll never be true for hugepd per any > known plan, but also it paves way for reusing the function outside > fast-gup. > > To make sure we'll still remember this issue just in case hugepd will be > extended to support non-hugetlbfs memories, add a rich comment above > gup_huge_pd(), explaining the issue with proper references. > > Cc: Christoph Hellwig > Cc: Lorenzo Stoakes > Cc: Michael Ellerman > Cc: linuxppc-dev@lists.ozlabs.org > Signed-off-by: Peter Xu > --- > mm/gup.c | 13 ++++++++----- > 1 file changed, 8 insertions(+), 5 deletions(-) Reviewed-by: Jason Gunthorpe Jason