From 55a8e1451869233db837a97e8f3cbf9983bc8678 Mon Sep 17 00:00:00 2001 From: "Aneesh Kumar K.V (Arm)" Date: Tue, 8 Sep 2026 17:02:32 +0530 Subject: [PATCH] x86/mm: Don't force unencrypted DMA for IOMMU-backed devices Commit 8277a12d0d60 ("dma-pool: track decrypted atomic pools and select them via attrs") exposed an issue with force_dma_unencrypted() on systems using host memory encryption. force_dma_unencrypted() checks whether the device DMA mask can address the encryption bit and, if not, requires DMA allocations to use unencrypted memory. However, this check is not applicable when the device is using the IOMMU. In that case, the device DMA mask constrains the IOVA seen by the device, not the backing physical address, so it does not need to cover the C-bit. This currently causes dma_alloc_attrs() to set __DMA_ATTR_ALLOC_CC_SHARED for such devices. iommu_dma_alloc() does not support that attribute and rejects the allocation, causing DMA allocations to fail. Do not force DMA allocations to be unencrypted when the device is using the IOMMU. This allows the IOMMU to map the encrypted physical pages as before and avoids incorrectly requesting CC_SHARED allocations. Fixes: 8277a12d0d60 ("dma-pool: track decrypted atomic pools and select them via attrs") Reported-by: Timo Witte Closes: https://lore.kernel.org/all/CANB4YXS=Nf-co3t8eMHtqrW4sn=1BDcP6o=EoTrgZm0WYMYTyw@mail.gmail.com/ Signed-off-by: Aneesh Kumar K.V (Arm) Link: https://lore.kernel.org/r/20260908113232.247457-1-aneesh.kumar@kernel.org [mszyprow: adjusted url and changed 'link' tag to the 'closes' one] Signed-off-by: Marek Szyprowski --- arch/x86/mm/mem_encrypt.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c index 95bae74fdab2..3aefdef5bcb0 100644 --- a/arch/x86/mm/mem_encrypt.c +++ b/arch/x86/mm/mem_encrypt.c @@ -13,6 +13,7 @@ #include #include #include +#include #include @@ -30,7 +31,7 @@ bool force_dma_unencrypted(struct device *dev) * device does not support DMA to addresses that include the * encryption mask. */ - if (cc_platform_has(CC_ATTR_HOST_MEM_ENCRYPT)) { + if (cc_platform_has(CC_ATTR_HOST_MEM_ENCRYPT) && !use_dma_iommu(dev)) { u64 dma_enc_mask = DMA_BIT_MASK(__ffs64(sme_me_mask)); u64 dma_dev_mask = min_not_zero(dev->coherent_dma_mask, dev->bus_dma_limit);