From cb2860ad6c4ff7e15bb69c7e3a6842bbea743229 Mon Sep 17 00:00:00 2001 From: Vasant Hegde Date: Tue, 11 Aug 2026 05:22:57 +0000 Subject: [PATCH] iommu/amd: Add SNP page mode 0 support Newer AMD IOMMUs supports DTE[Mode]=0 for SNP-enabled system. This is detected using new feature bit (EFR2[SNP_Page_Mode_0_Sup]). If this feature is enabled, then IOMMU supports: - Passthrough mode (i.e. iommu=pt) - amd_iommu=pgtbl_v2: Forcing Linux DMA-API to use IOMMU v2 page table - Setting up device for SVA mode in the host. Signed-off-by: Vasant Hegde Reviewed-by: Suravee Suthikulpanit Tested-by: Amandeep Kaur Longia Signed-off-by: Joerg Roedel --- drivers/iommu/amd/amd_iommu_types.h | 4 +++ drivers/iommu/amd/init.c | 42 ++++++++++++++++++++--------- drivers/iommu/amd/iommu.c | 4 +-- 3 files changed, 35 insertions(+), 15 deletions(-) diff --git a/drivers/iommu/amd/amd_iommu_types.h b/drivers/iommu/amd/amd_iommu_types.h index 36c0df418ce5..3dbe20023456 100644 --- a/drivers/iommu/amd/amd_iommu_types.h +++ b/drivers/iommu/amd/amd_iommu_types.h @@ -113,6 +113,7 @@ #define FEATURE_SNPAVICSUP_GAM(x) \ (FIELD_GET(FEATURE_SNPAVICSUP, x) == 0x1) #define FEATURE_HT_RANGE_IGNORE BIT_ULL(11) +#define FEATURE_SNP_PAGE_MODE0_SUP BIT_ULL(13) #define FEATURE_NUM_INT_REMAP_SUP GENMASK_ULL(9, 8) #define FEATURE_NUM_INT_REMAP_SUP_2K(x) \ @@ -419,6 +420,9 @@ extern bool amd_iommu_dump; pr_info(format, ## arg); \ } while(0); +/* SNP page mode 0 support */ +extern bool amd_iommu_snp_mode0_sup; + /* global flag if IOMMUs cache non-present entries */ extern bool amd_iommu_np_cache; /* Only true if all IOMMUs support device IOTLBs */ diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c index c0748521dff8..a1f85d44f2a4 100644 --- a/drivers/iommu/amd/init.c +++ b/drivers/iommu/amd/init.c @@ -180,6 +180,9 @@ bool amd_iommu_hatdis; bool amd_iommu_snp_en; EXPORT_SYMBOL(amd_iommu_snp_en); +/* SNP page mode 0 support */ +bool amd_iommu_snp_mode0_sup; + LIST_HEAD(amd_iommu_pci_seg_list); /* list of all PCI segments */ LIST_HEAD(amd_iommu_list); /* list of all AMD IOMMUs in the system */ LIST_HEAD(amd_ivhd_dev_flags_list); /* list of all IVHD device entry settings */ @@ -3394,18 +3397,28 @@ static __init void iommu_snp_enable(void) #ifdef CONFIG_KVM_AMD_SEV if (!cc_platform_has(CC_ATTR_HOST_SEV_SNP)) return; - /* - * The SNP support requires that IOMMU must be enabled, and is - * configured with V1 page table (DTE[Mode] = 0 is not supported). - */ - if (no_iommu || iommu_default_passthrough()) { - pr_warn("SNP: IOMMU disabled or configured in passthrough mode, SNP cannot be supported.\n"); + + /* SNP support required IOMMU to be ON */ + if (no_iommu) { + pr_warn("SNP: IOMMU disabled, SNP cannot be supported.\n"); goto disable_snp; } - if (amd_iommu_pgtable != PD_MODE_V1) { - pr_warn("SNP: IOMMU is configured with V2 page table mode, SNP cannot be supported.\n"); - goto disable_snp; + amd_iommu_snp_mode0_sup = check_feature2(FEATURE_SNP_PAGE_MODE0_SUP); + /* + * If SNP page mode 0 is not enabled, then SNP support requires that IOMMU + * must be configured with V1 page table (DTE[Mode] != 0). + */ + if (!amd_iommu_snp_mode0_sup) { + if (iommu_default_passthrough()) { + pr_warn("SNP: IOMMU configured in passthrough mode, SNP cannot be supported.\n"); + goto disable_snp; + } + + if (amd_iommu_pgtable != PD_MODE_V1) { + pr_warn("SNP: IOMMU is configured with V2 page table mode, SNP cannot be supported.\n"); + goto disable_snp; + } } amd_iommu_snp_en = check_feature(FEATURE_SNP); @@ -3940,12 +3953,15 @@ bool amd_iommu_pasid_supported(void) amd_iommu_gpt_level != PAGE_MODE_5_LEVEL) return false; + if (!amd_iommu_gt_ppr_supported()) + return false; + /* - * Since DTE[Mode]=0 is prohibited on SNP-enabled system - * (i.e. EFR[SNPSup]=1), IOMMUv2 page table cannot be used without - * setting up IOMMUv1 page table. + * If SNP page mode 0 is not supported, then DTE[Mode]=0 is prohibited + * on SNP-enabled system (i.e. EFR[SNPSup]=1). IOMMUv2 page table + * cannot be used without setting up IOMMUv1 page table. */ - return amd_iommu_gt_ppr_supported() && !amd_iommu_snp_en; + return (!amd_iommu_snp_en) || (amd_iommu_snp_en && amd_iommu_snp_mode0_sup); } struct amd_iommu *get_amd_iommu(unsigned int idx) diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c index 856948a5192c..4c31294fabc5 100644 --- a/drivers/iommu/amd/iommu.c +++ b/drivers/iommu/amd/iommu.c @@ -2953,9 +2953,9 @@ static int amd_iommu_identity_attach(struct iommu_domain *dom, struct device *de { /* * Don't allow attaching a device to the identity domain if SNP is - * enabled. + * enabled and SNP Mode0 support is not present. */ - if (amd_iommu_snp_en) + if (amd_iommu_snp_en && !amd_iommu_snp_mode0_sup) return -EINVAL; return amd_iommu_attach_device(dom, dev, old);