linux-kernel - [PATCH 9/9] iommu/amd: Set default domain to IDENTITY

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Message-ID: <20240430152430.4245-10-suravee.suthikulpanit@amd.com>
Date: Tue, 30 Apr 2024 15:24:30 +0000
From: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
To: <linux-kernel@...r.kernel.org>, <iommu@...ts.linux.dev>, <joro@...tes.org>
CC: <thomas.lendacky@....com>, <vasant.hegde@....com>, <michael.roth@....com>,
	<jon.grimm@....com>, <rientjes@...gle.com>, Suravee Suthikulpanit
	<suravee.suthikulpanit@....com>
Subject: [PATCH 9/9] iommu/amd: Set default domain to IDENTITY_DOMAIN when running in SEV guest

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@....com>
Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
---
 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