[PATCH v2] iommu/amd: Add SNP page mode 0 support

[PATCH v2] iommu/amd: Add SNP page mode 0 support

[Vasant Hegde]

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 <vasant.hegde@amd.com>
Reviewed-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Tested-by: Amandeep Kaur Longia <AmandeepKaur.Longia@amd.com>
---
Joerg,
  I have rebased this on top of amd/amd-vi branch and it should apply
  cleanly.

  Sorry. I missed to include this one along with PRI series. I think
  think one is ready. Can you please pick this up for 7.3

-Vasant

 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 3c292fdfa95a..d421151e9b7a 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) \
@@ -416,6 +417,9 @@ 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 563f9c2672d5..d8f626d7f784 100644
--- a/drivers/iommu/amd/iommu.c
+++ b/drivers/iommu/amd/iommu.c
@@ -2910,9 +2910,9 @@ 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);
-- 
2.31.1

Re: [PATCH v2] iommu/amd: Add SNP page mode 0 support

[Jörg Rödel]

On Tue, Aug 11, 2026 at 05:22:57AM +0000, Vasant Hegde wrote:
> Joerg,
>   I have rebased this on top of amd/amd-vi branch and it should apply
>   cleanly.
> 
>   Sorry. I missed to include this one along with PRI series. I think
>   think one is ready. Can you please pick this up for 7.3

All good, this now applied as well.