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Tsirkin" , Jason Wang , virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, Cornelia Huck , linux-s390@vger.kernel.org, Michael Mueller , Christian Borntraeger , Janosch Frank , Ram Pai , Thiago Jung Bauermann , Andy Lutomirski , Brijesh Singh Subject: Re: [PATCH 1/1] virtio_ring: fix return code on DMA mapping fails Message-ID: <20191129015730.GA13084@ashkalra_ubuntu_server> References: <20191114124646.74790-1-pasic@linux.ibm.com> <20191119121022.03aed69a.pasic@linux.ibm.com> <20191119080420-mutt-send-email-mst@kernel.org> <20191122140827.0ead345c.pasic@linux.ibm.com> <1ec7c229-6c4f-9351-efda-ed2df20f95f6@amd.com> <20191126184527.GA10481@lst.de> <20191128004225.GA11539@ashkalra_ubuntu_server> <20191128070538.GB20274@lst.de> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191128070538.GB20274@lst.de> User-Agent: Mutt/1.9.4 (2018-02-28) X-ClientProxiedBy: SN1PR12CA0066.namprd12.prod.outlook.com (2603:10b6:802:20::37) To DM6PR12MB3610.namprd12.prod.outlook.com (2603:10b6:5:3a::21) MIME-Version: 1.0 X-Originating-IP: [165.204.77.1] X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-HT: Tenant X-MS-Office365-Filtering-Correlation-Id: d3d0f977-799b-4732-5b91-08d7746f90db X-MS-TrafficTypeDiagnostic: DM6PR12MB4075:|DM6PR12MB4075: X-MS-Exchange-Transport-Forked: True X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:2887; X-Forefront-PRVS: 0236114672 X-Forefront-Antispam-Report: SFV:NSPM;SFS:(10009020)(7916004)(4636009)(366004)(396003)(39860400002)(136003)(346002)(376002)(189003)(199004)(6512007)(33716001)(7736002)(6486002)(6246003)(6436002)(81166006)(9686003)(8676002)(4326008)(81156014)(8936002)(2906002)(76176011)(52116002)(99286004)(26005)(44832011)(386003)(23726003)(6116002)(16586007)(58126008)(316002)(5660300002)(6506007)(54906003)(446003)(11346002)(7416002)(14454004)(3846002)(1076003)(86362001)(478600001)(6916009)(6666004)(47776003)(66066001)(25786009)(50466002)(186003)(66556008)(66476007)(305945005)(66946007)(33656002)(229853002);DIR:OUT;SFP:1101;SCL:1;SRVR:DM6PR12MB4075;H:DM6PR12MB3610.namprd12.prod.outlook.com;FPR:;SPF:None;LANG:en;PTR:InfoNoRecords;MX:1;A:1; Received-SPF: None (protection.outlook.com: amd.com does not designate permitted sender hosts) X-MS-Exchange-SenderADCheck: 1 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: 3h0zwu9ANicvvNt1q+K6LTqWxg7XkVRdiC3bTbTL74PKiUi2muvb+l8/j76OTWyfnNNQFXb8WX5mHGzfof4BTeDrmsXpLD4kcCLY29iHOKcjVFSz4MGTRukuUplzaS+ToCRezqwrSp9zwhNU5b4M3zfiheeF7ttMh+SHwMPv1Mpif2/UQvN18g4UoMfD+123UXXtRx4JzORqEW2ud0S3JlZ+R9i+TSfmbitF9V40d8Np2BXI+6YP2FjBJ+VcAc80ZrQ4xRgx6r0BJFVJqqLjpcujpS6LT5z2o+VmEDqa2gSda3scfoHoNawDyp176z9gh1HwHZrsj3G9xgtoqHUQRXV/dBQqUik6dLTRwnoFdhq7j7hGVyWR8IM5TNAaA6bJESyPwRAyz/5GZ2IEfPJSMfHa3bid97C6VRtKhHZGh8T+j/PRu1KrStB08rHRG+Kh X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-Network-Message-Id: d3d0f977-799b-4732-5b91-08d7746f90db X-MS-Exchange-CrossTenant-OriginalArrivalTime: 29 Nov 2019 01:58:02.0689 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: RJDv0xbU4KCNcZpWwcwhdJQlmiYY9o8L2MuCEE6s+9KZfCzu/kcw57Jv3x9uQEBzaNxZSDEWp1FktRF76Ck5IQ== X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM6PR12MB4075 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Nov 28, 2019 at 08:05:38AM +0100, Christoph Hellwig wrote: > On Thu, Nov 28, 2019 at 12:42:25AM +0000, Ashish Kalra wrote: > > Why can't we leverage CMA instead of SWIOTLB for DMA when SEV is > > enabled, CMA is well integerated with the DMA subsystem and handles > > encrypted pages when force_dma_unencrypted() returns TRUE. > > > > Though, CMA might face the same issues as SWIOTLB bounce buffers, it's > > size is similarly setup statically as SWIOTLB does or can be set as a > > percentage of the available system memory. > > How is CMA integrated with SEV? CMA just gives a contiguous chunk > of memory, which still needs to be remapped as unencrypted before > returning it to the user. Looking at the implementation, i see that CMA is accessible using dma_alloc_coherent() and the buffer allocated by dma_alloc_coherent() either using the CMA or the page allocator, will be marked/tagged as unencrypted and returned to the user. But for dma_map_xx() interfaces, the memory will need be remapped as unencrypted memory (as you mentioned). Thanks, Ashish