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Thu, 25 Mar 2021 12:09:19 +0000 Subject: Re: [RFC PATCH 1/2] mm,drm/ttm: Block fast GUP to TTM huge pages To: Jason Gunthorpe , =?UTF-8?Q?Thomas_Hellstr=c3=b6m_=28Intel=29?= Cc: David Airlie , linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-mm@kvack.org, Andrew Morton References: <0b984f96-00fb-5410-bb16-02e12b2cc024@shipmail.org> <20210324163812.GJ2356281@nvidia.com> <08f19e80-d6cb-8858-0c5d-67d2e2723f72@amd.com> <730eb2ff-ba98-2393-6d42-61735e3c6b83@shipmail.org> <20210324231419.GR2356281@nvidia.com> <607ecbeb-e8a5-66e9-6fe2-9a8d22f12bc2@shipmail.org> <15da5784-96ca-25e5-1485-3ce387ee6695@shipmail.org> <20210325113023.GT2356281@nvidia.com> <20210325120103.GV2356281@nvidia.com> From: =?UTF-8?Q?Christian_K=c3=b6nig?= Message-ID: Date: Thu, 25 Mar 2021 13:09:14 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.1 In-Reply-To: <20210325120103.GV2356281@nvidia.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Originating-IP: [2a02:908:1252:fb60:72d1:2a48:a80e:e149] X-ClientProxiedBy: AM0PR04CA0032.eurprd04.prod.outlook.com (2603:10a6:208:122::45) To MN2PR12MB3775.namprd12.prod.outlook.com (2603:10b6:208:159::19) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [IPv6:2a02:908:1252:fb60:72d1:2a48:a80e:e149] (2a02:908:1252:fb60:72d1:2a48:a80e:e149) by AM0PR04CA0032.eurprd04.prod.outlook.com (2603:10a6:208:122::45) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3977.28 via Frontend Transport; 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The point here was that in this case, to make sure mmap uses the >> correct VA to give us a reasonable chance of alignement, the driver might >> need to be aware of and do trickery with the huge page-table-entry sizes >> anyway, although I think in most cases a standard helper for this can be >> supplied. > Of course the driver needs some way to influence the VA mmap uses, > gernally it should align to the natural page size of the device Well a mmap() needs to be aligned to the page size of the CPU, but not necessarily to the one of the device. So I'm pretty sure the device driver should not be involved in any way the choosing of the VA for the CPU mapping. Christian. > > Jason