Also switch to enable vIOMMU by default, and provide kernel boot option to
disable the feature.

Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
---
 drivers/iommu/amd/amd_iommu.h       |  1 +
 drivers/iommu/amd/amd_iommu_types.h |  3 +++
 drivers/iommu/amd/init.c            | 14 +++++++++++++-
 drivers/iommu/amd/viommu.c          | 16 ++++++++++++++++
 4 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/amd/amd_iommu.h b/drivers/iommu/amd/amd_iommu.h
index 38694ebdb083..2b057ab77ce8 100644
--- a/drivers/iommu/amd/amd_iommu.h
+++ b/drivers/iommu/amd/amd_iommu.h
@@ -25,6 +25,7 @@ void amd_iommu_restart_ga_log(struct amd_iommu *iommu);
 void amd_iommu_restart_ppr_log(struct amd_iommu *iommu);
 void amd_iommu_set_rlookup_table(struct amd_iommu *iommu, u16 devid);
 void iommu_feature_enable(struct amd_iommu *iommu, u8 bit);
+bool iommu_feature_enable_and_check(struct amd_iommu *iommu, u8 bit);
 void *__init iommu_alloc_4k_pages(struct amd_iommu *iommu,
 				  gfp_t gfp, size_t size);
 u8 __iomem * __init iommu_map_mmio_space(u64 address, u64 end);
diff --git a/drivers/iommu/amd/amd_iommu_types.h b/drivers/iommu/amd/amd_iommu_types.h
index ff72023fa512..4667efcfb8e9 100644
--- a/drivers/iommu/amd/amd_iommu_types.h
+++ b/drivers/iommu/amd/amd_iommu_types.h
@@ -204,9 +204,12 @@
 #define CONTROL_EPH_EN		45
 #define CONTROL_PPR_AUTO_RSP_AON 48
 #define CONTROL_XT_EN		50
+#define CONTROL_VCMD_EN         52
+#define CONTROL_VIOMMU_EN       53
 #define CONTROL_INTCAPXT_EN	51
 #define CONTROL_GCR3TRPMODE	58
 #define CONTROL_IRTCACHEDIS	59
+#define CONTROL_GSTBUFFERTRPMODE	60
 #define CONTROL_SNPAVIC_EN	61
 
 #define CTRL_INV_TO_MASK	7
diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
index 0018ae804ab4..63271f4305de 100644
--- a/drivers/iommu/amd/init.c
+++ b/drivers/iommu/amd/init.c
@@ -195,7 +195,7 @@ bool amdr_ivrs_remap_support __read_mostly;
 bool amd_iommu_force_isolation __read_mostly;
 
 /* VIOMMU enabling flag */
-bool amd_iommu_viommu;
+bool amd_iommu_viommu = true;
 
 unsigned long amd_iommu_pgsize_bitmap __ro_after_init = AMD_IOMMU_PGSIZES;
 
@@ -436,6 +436,16 @@ void iommu_feature_enable(struct amd_iommu *iommu, u8 bit)
 	iommu_feature_set(iommu, 1ULL, 1ULL, bit);
 }
 
+bool iommu_feature_enable_and_check(struct amd_iommu *iommu, u8 bit)
+{
+	u64 ctrl;
+
+	iommu_feature_enable(iommu, bit);
+
+	ctrl = readq(iommu->mmio_base +  MMIO_CONTROL_OFFSET);
+	return (ctrl & (1ULL << bit));
+}
+
 static void iommu_feature_disable(struct amd_iommu *iommu, u8 bit)
 {
 	iommu_feature_set(iommu, 0ULL, 1ULL, bit);
@@ -3702,6 +3712,8 @@ static int __init parse_amd_iommu_options(char *str)
 		} else if (strncmp(str, "v2_pgsizes_only", 15) == 0) {
 			pr_info("Restricting V1 page-sizes to 4KiB/2MiB/1GiB");
 			amd_iommu_pgsize_bitmap = AMD_IOMMU_PGSIZES_V2;
+		} else if (strncmp(str, "viommu_disable", 14) == 0) {
+			amd_iommu_viommu = false;
 		} else {
 			pr_notice("Unknown option - '%s'\n", str);
 		}
diff --git a/drivers/iommu/amd/viommu.c b/drivers/iommu/amd/viommu.c
index 4626134893d6..5c744de729d5 100644
--- a/drivers/iommu/amd/viommu.c
+++ b/drivers/iommu/amd/viommu.c
@@ -45,6 +45,18 @@
 
 LIST_HEAD(viommu_devid_map);
 
+static int viommu_enable(struct amd_iommu *iommu)
+{
+	/* The GstBufferTRPMode feature is checked by set and test */
+	if (!iommu_feature_enable_and_check(iommu, CONTROL_GSTBUFFERTRPMODE))
+		return -EINVAL;
+
+	iommu_feature_enable(iommu, CONTROL_VCMD_EN);
+	iommu_feature_enable(iommu, CONTROL_VIOMMU_EN);
+
+	return 0;
+}
+
 static int viommu_init_pci_vsc(struct amd_iommu *iommu)
 {
 	iommu->vsc_offset = pci_find_capability(iommu->dev, PCI_CAP_ID_VNDR);
@@ -298,6 +310,10 @@ int __init amd_viommu_init(struct amd_iommu *iommu)
 
 	set_iommu_dte(iommu);
 
+	ret = viommu_enable(iommu);
+	if (ret)
+		return ret;
+
 	return 0;
 }
 
-- 
2.34.1

On Mon, Mar 30, 2026 at 08:42:06AM +0000, Suravee Suthikulpanit wrote:
> Also switch to enable vIOMMU by default, and provide kernel boot option to
> disable the feature.

Why? userspace is free to not use it, lets not pollute the kernel
command line.

Jason