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Wed, 15 Jan 2025 13:38:22 +0000 Received: from CH3PR12MB8659.namprd12.prod.outlook.com ([fe80::6eb6:7d37:7b4b:1732]) by CH3PR12MB8659.namprd12.prod.outlook.com ([fe80::6eb6:7d37:7b4b:1732%5]) with mapi id 15.20.8335.017; Wed, 15 Jan 2025 13:38:22 +0000 Date: Wed, 15 Jan 2025 09:38:21 -0400 From: Jason Gunthorpe To: Christian =?utf-8?B?S8O2bmln?= Cc: Xu Yilun , Christoph Hellwig , Leon Romanovsky , kvm@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-media@vger.kernel.org, linaro-mm-sig@lists.linaro.org, sumit.semwal@linaro.org, pbonzini@redhat.com, seanjc@google.com, alex.williamson@redhat.com, vivek.kasireddy@intel.com, dan.j.williams@intel.com, aik@amd.com, yilun.xu@intel.com, linux-coco@lists.linux.dev, linux-kernel@vger.kernel.org, lukas@wunner.de, yan.y.zhao@intel.com, leon@kernel.org, baolu.lu@linux.intel.com, zhenzhong.duan@intel.com, tao1.su@intel.com Subject: Re: [RFC PATCH 01/12] dma-buf: Introduce dma_buf_get_pfn_unlocked() kAPI Message-ID: <20250115133821.GO5556@nvidia.com> References: <20250108145843.GR5556@nvidia.com> <5a858e00-6fea-4a7a-93be-f23b66e00835@amd.com> <20250108162227.GT5556@nvidia.com> <58e97916-e6fd-41ef-84b4-bbf53ed0e8e4@amd.com> <20250110205454.GM5556@nvidia.com> Content-Type: text/plain; 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IMHO the second part of preventing > > machine checks is not complete. > > > > In the approach I have been talking about the secure memory would be > > represented by a p2p_provider structure that is incompatible with > > everything else. For instance importers that can only do DMA would > > simply cleanly fail when presented with this memory. > > That's a rather interesting use case, but not something I consider fitting > for the DMA-buf interface. To recast the problem statement, it is basically the same as your device private interconnects. There are certain devices that understand how to use this memory, and if they work together they can access it. > See DMA-buf in meant to be used between drivers to allow DMA access on > shared buffers. They are shared, just not with everyone :) > What you try to do here instead is to give memory in the form of a file > descriptor to a client VM to do things like CPU mapping and giving it to > drivers to do DMA etc... How is this paragraph different from the first? It is a shared buffer that we want real DMA and CPU "DMA" access to. It is "private" so things that don't understand the interconnect rules cannot access it. > That sounds more something for the TEE driver instead of anything DMA-buf > should be dealing with. Has nothing to do with TEE. Jason