[PATCH 9/9] iommu/amd: Set default domain to IDENTITY_DOMAIN when running in SEV guest

[Suravee Suthikulpanit]

Since SEV guest depends on the unencrypted swiotlb bounce buffer
to support DMA, the guest AMD IOMMU driver must be force to setup to
pass-through mode.

Suggested-by: Thomas Lendacky <thomas.lendacky@xxxxxxx>
Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
---
 drivers/iommu/amd/init.c  | 15 +++++++++++++++
 drivers/iommu/amd/iommu.c |  6 ++++++
 2 files changed, 21 insertions(+)

diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
index b3ff89952c7f..1dccf030f674 100644
--- a/drivers/iommu/amd/init.c
+++ b/drivers/iommu/amd/init.c
@@ -3179,6 +3179,20 @@ static bool __init detect_ivrs(void)
 	return true;
 }
 
+static void iommu_sev_guest_enable(void)
+{
+	/*
+	 * Force IOMMU default domain to pass-through for
+	 * SEV guest since we cannot support DMA-remapping.
+	 * Note: This check must be done after IOMMU_ENABLED state.
+	 */
+	if (!cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT))
+		return;
+
+	pr_info("Force pass-through for SEV guest\n");
+	iommu_set_default_passthrough(false);
+}
+
 static void iommu_snp_enable(void)
 {
 #ifdef CONFIG_KVM_AMD_SEV
@@ -3247,6 +3261,7 @@ static int __init state_next(void)
 		break;
 	case IOMMU_ENABLED:
 		register_syscore_ops(&amd_iommu_syscore_ops);
+		iommu_sev_guest_enable();
 		iommu_snp_enable();
 		ret = amd_iommu_init_pci();
 		init_state = ret ? IOMMU_INIT_ERROR : IOMMU_PCI_INIT;
diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
index f98a10b7925b..c985d23c8528 100644
--- a/drivers/iommu/amd/iommu.c
+++ b/drivers/iommu/amd/iommu.c
@@ -2876,6 +2876,12 @@ static int amd_iommu_def_domain_type(struct device *dev)
 		return IOMMU_DOMAIN_IDENTITY;
 	}
 
+	/*
+	 * Force identity map for SEV guest.
+	 */
+	if (cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT))
+		return IOMMU_DOMAIN_IDENTITY;
+
 	return 0;
 }
 
-- 
2.34.1