[PATCH v5 03/24] iommu/amd: Detect and initialize AMD vIOMMU feature

[Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>]

The feature is advertised w/ EFR[VIOMMUSup]. Please see the AMD IOMMU
specification[1] for more detail.

Gate amd_viommu_init() on this IOMMU's EFR[VIOMMUSup]
(iommu->features) at the PCI init call site. Do not use
check_feature()/amd_iommu_efr; that global mask is the AND of
every IOMMU. Do not fail other IOMMUs when one instance lacks
the bit or init fails.

Set AMD_IOMMU_FLAG_VIOMMU_EN when amd_viommu_init() succeeds.
Log PCI names of IOMMUs that have that flag set.

Forward-declare struct amd_iommu in amd_viommu.h so the header
is self-contained.

When CONFIG_AMD_IOMMU_IOMMUFD is off, the amd_viommu_init() stub
returns 0 so a missing build is not logged as an init failure on
EFR[VIOMMUSup] hardware.

[1] https://docs.amd.com/v/u/en-US/48882_3.11_IOMMU_PUB

Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
---
 drivers/iommu/amd/Makefile          |  2 +-
 drivers/iommu/amd/amd_iommu.h       |  5 +++++
 drivers/iommu/amd/amd_iommu_types.h |  2 ++
 drivers/iommu/amd/amd_viommu.h      | 29 ++++++++++++++++++++++++
 drivers/iommu/amd/init.c            | 34 +++++++++++++++++++++++++++++
 drivers/iommu/amd/viommu.c          | 25 +++++++++++++++++++++
 6 files changed, 96 insertions(+), 1 deletion(-)
 create mode 100644 drivers/iommu/amd/amd_viommu.h
 create mode 100644 drivers/iommu/amd/viommu.c

diff --git a/drivers/iommu/amd/Makefile b/drivers/iommu/amd/Makefile
index 94b8ef2acb18..e1e824b9c7b0 100644
--- a/drivers/iommu/amd/Makefile
+++ b/drivers/iommu/amd/Makefile
@@ -1,4 +1,4 @@
 # SPDX-License-Identifier: GPL-2.0-only
 obj-y += iommu.o init.o quirks.o ppr.o pasid.o
-obj-$(CONFIG_AMD_IOMMU_IOMMUFD) += iommufd.o nested.o
+obj-$(CONFIG_AMD_IOMMU_IOMMUFD) += iommufd.o nested.o viommu.o
 obj-$(CONFIG_AMD_IOMMU_DEBUGFS) += debugfs.o
diff --git a/drivers/iommu/amd/amd_iommu.h b/drivers/iommu/amd/amd_iommu.h
index 71113e860859..b2ae17e3df34 100644
--- a/drivers/iommu/amd/amd_iommu.h
+++ b/drivers/iommu/amd/amd_iommu.h
@@ -112,6 +112,11 @@ static inline bool check_feature(u64 mask)
 	return (amd_iommu_efr & mask);
 }
 
+static inline bool amd_iommu_viommu_enabled(struct amd_iommu *iommu)
+{
+	return iommu && (iommu->flags & AMD_IOMMU_FLAG_VIOMMU_EN);
+}
+
 static inline bool check_feature2(u64 mask)
 {
 	return (amd_iommu_efr2 & mask);
diff --git a/drivers/iommu/amd/amd_iommu_types.h b/drivers/iommu/amd/amd_iommu_types.h
index 704b4c8acdc5..688cd9240790 100644
--- a/drivers/iommu/amd/amd_iommu_types.h
+++ b/drivers/iommu/amd/amd_iommu_types.h
@@ -91,6 +91,7 @@
 #define FEATURE_HASUP		BIT_ULL(49)
 #define FEATURE_EPHSUP		BIT_ULL(50)
 #define FEATURE_HDSUP		BIT_ULL(52)
+#define FEATURE_VIOMMU		BIT_ULL(55)
 #define FEATURE_SNP		BIT_ULL(63)
 
 
@@ -465,6 +466,7 @@ struct irq_domain;
 struct amd_irte_ops;
 
 #define AMD_IOMMU_FLAG_TRANS_PRE_ENABLED      (1 << 0)
+#define AMD_IOMMU_FLAG_VIOMMU_EN              (1 << 1)
 
 struct gcr3_tbl_info {
 	u64	*gcr3_tbl;	/* Guest CR3 table */
diff --git a/drivers/iommu/amd/amd_viommu.h b/drivers/iommu/amd/amd_viommu.h
new file mode 100644
index 000000000000..864e7b283cff
--- /dev/null
+++ b/drivers/iommu/amd/amd_viommu.h
@@ -0,0 +1,29 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2026 Advanced Micro Devices, Inc.
+ */
+
+#ifndef AMD_VIOMMU_H
+#define AMD_VIOMMU_H
+
+struct amd_iommu;
+
+#if IS_ENABLED(CONFIG_AMD_IOMMU_IOMMUFD)
+
+int amd_viommu_init(struct amd_iommu *iommu);
+
+#else
+
+/*
+ * CONFIG_AMD_IOMMU_IOMMUFD is off: host vIOMMU is not compiled in.
+ * Succeed as a no-op so iommu_init_pci() does not pr_err on
+ * EFR[VIOMMUSup] hardware.
+ */
+static inline int amd_viommu_init(struct amd_iommu *iommu)
+{
+	return 0;
+}
+
+#endif /* CONFIG_AMD_IOMMU_IOMMUFD */
+
+#endif /* AMD_VIOMMU_H */
diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
index 8a410d4aa370..c80872ce0b60 100644
--- a/drivers/iommu/amd/init.c
+++ b/drivers/iommu/amd/init.c
@@ -34,6 +34,7 @@
 #include <linux/crash_dump.h>
 
 #include "amd_iommu.h"
+#include "amd_viommu.h"
 #include "../irq_remapping.h"
 #include "../iommu-pages.h"
 
@@ -2196,6 +2197,19 @@ static int __init iommu_init_pci(struct amd_iommu *iommu)
 	if (check_feature(FEATURE_PPR) && amd_iommu_alloc_ppr_log(iommu))
 		return -ENOMEM;
 
+	/*
+	 * vIOMMU is advertised in this IOMMU's EFR[VIOMMUSup]
+	 * (iommu->features). Do not use check_feature()/amd_iommu_efr;
+	 * that global mask is the AND of every IOMMU and can hide the
+	 * bit on mixed systems.
+	 */
+	if (iommu->features & FEATURE_VIOMMU) {
+		ret = amd_viommu_init(iommu);
+		if (ret)
+			pr_err("Failed to initialize vIOMMU on %s\n",
+			       pci_name(iommu->dev));
+	}
+
 	if (iommu->cap & (1UL << IOMMU_CAP_NPCACHE)) {
 		pr_info("Using strict mode due to virtualization\n");
 		iommu_set_dma_strict();
@@ -2264,6 +2278,25 @@ static int __init iommu_init_pci(struct amd_iommu *iommu)
 	return pci_enable_device(iommu->dev);
 }
 
+static void print_viommu_info(void)
+{
+	struct amd_iommu *iommu;
+	const char *sep = "";
+
+	for_each_iommu(iommu) {
+		if (!amd_iommu_viommu_enabled(iommu))
+			continue;
+		if (!sep[0])
+			pr_info("vIOMMU enabled: ");
+		else
+			pr_cont("%s", sep);
+		pr_cont("%s", pci_name(iommu->dev));
+		sep = ", ";
+	}
+	if (sep[0])
+		pr_cont("\n");
+}
+
 static void print_iommu_info(void)
 {
 	int i;
@@ -2301,6 +2334,7 @@ static void print_iommu_info(void)
 		pr_info("V2 page table enabled (Paging mode : %d level)\n",
 			amd_iommu_gpt_level);
 	}
+	print_viommu_info();
 }
 
 static int __init amd_iommu_init_pci(void)
diff --git a/drivers/iommu/amd/viommu.c b/drivers/iommu/amd/viommu.c
new file mode 100644
index 000000000000..53f3302f7cc6
--- /dev/null
+++ b/drivers/iommu/amd/viommu.c
@@ -0,0 +1,25 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2026 Advanced Micro Devices, Inc.
+ */
+
+#define pr_fmt(fmt)     "AMD-Vi: " fmt
+#define dev_fmt(fmt)    pr_fmt(fmt)
+
+#include <linux/iommu.h>
+#include <linux/iommufd.h>
+#include <uapi/linux/iommufd.h>
+
+#include <asm/iommu.h>
+#include <asm/set_memory.h>
+
+#include "iommufd.h"
+#include "amd_iommu.h"
+#include "amd_iommu_types.h"
+#include "amd_viommu.h"
+
+int __init amd_viommu_init(struct amd_iommu *iommu)
+{
+	iommu->flags |= AMD_IOMMU_FLAG_VIOMMU_EN;
+	return 0;
+}
-- 
2.34.1