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[159.2.73.22]) by smtp.gmail.com with ESMTPSA id af79cd13be357-8cfc8f91d32sm1083581885a.14.2026.03.24.12.11.44 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 24 Mar 2026 12:11:44 -0700 (PDT) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1w57AF-00000000JZi-3000; Tue, 24 Mar 2026 16:11:43 -0300 Date: Tue, 24 Mar 2026 16:11:43 -0300 From: Jason Gunthorpe To: Jiri Pirko Cc: Robin Murphy , dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, iommu@lists.linux.dev, linux-media@vger.kernel.org, sumit.semwal@linaro.org, benjamin.gaignard@collabora.com, Brian.Starkey@arm.com, jstultz@google.com, tjmercier@google.com, christian.koenig@amd.com, m.szyprowski@samsung.com, leon@kernel.org, sean.anderson@linux.dev, ptesarik@suse.com, catalin.marinas@arm.com, aneesh.kumar@kernel.org, suzuki.poulose@arm.com, steven.price@arm.com, thomas.lendacky@amd.com, john.allen@amd.com, ashish.kalra@amd.com, suravee.suthikulpanit@amd.com, linux-coco@lists.linux.dev Subject: Re: [PATCH v4 1/2] dma-mapping: introduce DMA_ATTR_CC_DECRYPTED for pre-decrypted memory Message-ID: <20260324191143.GF8437@ziepe.ca> References: <20260316125857.617836-1-jiri@resnulli.us> <20260316125857.617836-2-jiri@resnulli.us> <15fcfa5e-c4b9-4b56-8f84-20dd5f66d643@arm.com> Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Tue, Mar 17, 2026 at 09:26:21AM +0100, Jiri Pirko wrote: > >...although, why *shouldn't* this be allowed with a vIOMMU? (Especially given > >that a vIOMMU for untrusted devices can be emulated by the host VMM without > >the CoCo hypervisor having to care at all - again, at least on Arm and other > >architectures where IOMMUs are regular driver model devices) > > Well, when iommu path is able to consume the attr, this restriction > should be lifted. This is basically a sanity check for the > dma_map_phys() caller. Right we eventually need a matching IOMMU_DECRYPTED. It needs to mirror how the CPUs work - any place that would use pgprot_decrypted to create a PTE should use IOMMU_PROT_DECRYPTED to create an iommu mapping. The current hack in AMD assumes IOMMU_DECRYPTED behavior for IOMMU_MMIO, but that isn't general enough.. There is some maze to get there but for the moment I think it is fine to just not support vIOMMU, it isn't like any vIOMMU drivers even exist for CC VMs right now. Jason