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Mon, 23 Feb 2026 01:51:38 -0800 (PST) From: Jiri Pirko To: dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, iommu@lists.linux.dev, linux-media@vger.kernel.org Cc: 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, robin.murphy@arm.com, jgg@ziepe.ca, 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: [PATCH v2 1/2] dma-mapping: introduce DMA_ATTR_CC_DECRYPTED for pre-decrypted memory Date: Mon, 23 Feb 2026 10:51:35 +0100 Message-ID: <20260223095136.225277-2-jiri@resnulli.us> X-Mailer: git-send-email 2.51.1 In-Reply-To: <20260223095136.225277-1-jiri@resnulli.us> References: <20260223095136.225277-1-jiri@resnulli.us> Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Jiri Pirko Current CC designs don't place a vIOMMU in front of untrusted devices. Instead, the DMA API forces all untrusted device DMA through swiotlb bounce buffers (is_swiotlb_force_bounce()) which copies data into decrypted memory on behalf of the device. When a caller has already arranged for the memory to be decrypted via set_memory_decrypted(), the DMA API needs to know so it can map directly using the unencrypted physical address rather than bounce buffering. Following the pattern of DMA_ATTR_MMIO, add DMA_ATTR_CC_DECRYPTED for this purpose. Like the MMIO case, only the caller knows what kind of memory it has and must inform the DMA API for it to work correctly. Signed-off-by: Jiri Pirko --- v1->v2: - rebased on top of recent dma-mapping-fixes --- include/linux/dma-mapping.h | 6 ++++++ include/trace/events/dma.h | 3 ++- kernel/dma/direct.h | 14 +++++++++++--- 3 files changed, 19 insertions(+), 4 deletions(-) diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h index 29973baa0581..ae3d85e494ec 100644 --- a/include/linux/dma-mapping.h +++ b/include/linux/dma-mapping.h @@ -85,6 +85,12 @@ * a cacheline must have this attribute for this to be considered safe. */ #define DMA_ATTR_CPU_CACHE_CLEAN (1UL << 11) +/* + * DMA_ATTR_CC_DECRYPTED: Indicates memory that has been explicitly decrypted + * (shared) for confidential computing guests. The caller must have + * called set_memory_decrypted(). A struct page is required. + */ +#define DMA_ATTR_CC_DECRYPTED (1UL << 12) /* * A dma_addr_t can hold any valid DMA or bus address for the platform. It can diff --git a/include/trace/events/dma.h b/include/trace/events/dma.h index 33e99e792f1a..b8082d5177c4 100644 --- a/include/trace/events/dma.h +++ b/include/trace/events/dma.h @@ -32,7 +32,8 @@ TRACE_DEFINE_ENUM(DMA_NONE); { DMA_ATTR_ALLOC_SINGLE_PAGES, "ALLOC_SINGLE_PAGES" }, \ { DMA_ATTR_NO_WARN, "NO_WARN" }, \ { DMA_ATTR_PRIVILEGED, "PRIVILEGED" }, \ - { DMA_ATTR_MMIO, "MMIO" }) + { DMA_ATTR_MMIO, "MMIO" }, \ + { DMA_ATTR_CC_DECRYPTED, "CC_DECRYPTED" }) DECLARE_EVENT_CLASS(dma_map, TP_PROTO(struct device *dev, phys_addr_t phys_addr, dma_addr_t dma_addr, diff --git a/kernel/dma/direct.h b/kernel/dma/direct.h index e89f175e9c2d..c047a9d0fda3 100644 --- a/kernel/dma/direct.h +++ b/kernel/dma/direct.h @@ -84,16 +84,24 @@ static inline dma_addr_t dma_direct_map_phys(struct device *dev, dma_addr_t dma_addr; if (is_swiotlb_force_bounce(dev)) { - if (attrs & DMA_ATTR_MMIO) - return DMA_MAPPING_ERROR; + if (!(attrs & DMA_ATTR_CC_DECRYPTED)) { + if (attrs & DMA_ATTR_MMIO) + return DMA_MAPPING_ERROR; - return swiotlb_map(dev, phys, size, dir, attrs); + return swiotlb_map(dev, phys, size, dir, attrs); + } + } else if (attrs & DMA_ATTR_CC_DECRYPTED) { + return DMA_MAPPING_ERROR; } if (attrs & DMA_ATTR_MMIO) { dma_addr = phys; if (unlikely(!dma_capable(dev, dma_addr, size, false))) goto err_overflow; + } else if (attrs & DMA_ATTR_CC_DECRYPTED) { + dma_addr = phys_to_dma_unencrypted(dev, phys); + if (unlikely(!dma_capable(dev, dma_addr, size, false))) + goto err_overflow; } else { dma_addr = phys_to_dma(dev, phys); if (unlikely(!dma_capable(dev, dma_addr, size, true)) || -- 2.51.1