AMD IOMMU Extended Feature (EFR) and Extended Feature 2 (EFR2) registers
specify features supported by each IOMMU hardware instance.
The IOMMU driver checks each feature-specific bits before enabling
each feature at run time.

For IOMMUFD, the hypervisor passes the raw value of amd_iommu_efr and
amd_iommu_efr2 to VMM via iommufd IOMMU_DEVICE_GET_HW_INFO ioctl.

Reviewed-by: Nicolin Chen <nicolinc@nvidia.com>
Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
---
Change in v4:
 * Add CONFIG_AMD_IOMMU_IOMMUFD
 * Update comment regarding EFR/EFR2 from struct iommu_hw_info_amd.

Change in v3:
 * Remove extern
 * Fix link to IOMMU spec
 * Update kdoc

Change in v2:
 * Do not mask the EFR/EFR2 and simply return the value reported by hardware
 * Move amd_iommufd_hw_info() to drivers/iommu/amd/iommufd.c
 * Also support IOMMU_HW_INFO_TYPE_DEFAULT

 drivers/iommu/amd/Kconfig    | 10 ++++++++++
 drivers/iommu/amd/Makefile   |  1 +
 drivers/iommu/amd/iommu.c    |  2 ++
 drivers/iommu/amd/iommufd.c  | 31 +++++++++++++++++++++++++++++++
 drivers/iommu/amd/iommufd.h  | 15 +++++++++++++++
 include/uapi/linux/iommufd.h | 28 ++++++++++++++++++++++++++++
 6 files changed, 87 insertions(+)
 create mode 100644 drivers/iommu/amd/iommufd.c
 create mode 100644 drivers/iommu/amd/iommufd.h

diff --git a/drivers/iommu/amd/Kconfig b/drivers/iommu/amd/Kconfig
index ecef69c11144..f4b9b1d1c3c7 100644
--- a/drivers/iommu/amd/Kconfig
+++ b/drivers/iommu/amd/Kconfig
@@ -27,6 +27,16 @@ config AMD_IOMMU
 	  your BIOS for an option to enable it or if you have an IVRS ACPI
 	  table.
 
+config AMD_IOMMU_IOMMUFD
+	bool "Enable IOMMUFD features for AMD IOMMU (EXPERIMENTAL)"
+	depends on IOMMUFD
+	depends on AMD_IOMMU
+	help
+	  Support for IOMMUFD features intended to support virtual machines
+	  with accelerated virtual IOMMUs.
+
+	  Say Y here if you are doing development and testing on this feature.
+
 config AMD_IOMMU_DEBUGFS
 	bool "Enable AMD IOMMU internals in DebugFS"
 	depends on AMD_IOMMU && IOMMU_DEBUGFS
diff --git a/drivers/iommu/amd/Makefile b/drivers/iommu/amd/Makefile
index 59c04a67f398..5ae46d99a45b 100644
--- a/drivers/iommu/amd/Makefile
+++ b/drivers/iommu/amd/Makefile
@@ -1,3 +1,4 @@
 # SPDX-License-Identifier: GPL-2.0-only
 obj-y += iommu.o init.o quirks.o io_pgtable.o io_pgtable_v2.o ppr.o pasid.o
+obj-$(CONFIG_AMD_IOMMU_IOMMUFD) += iommufd.o
 obj-$(CONFIG_AMD_IOMMU_DEBUGFS) += debugfs.o
diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
index eb348c63a8d0..344364ef94f8 100644
--- a/drivers/iommu/amd/iommu.c
+++ b/drivers/iommu/amd/iommu.c
@@ -42,6 +42,7 @@
 #include <uapi/linux/iommufd.h>
 
 #include "amd_iommu.h"
+#include "iommufd.h"
 #include "../dma-iommu.h"
 #include "../irq_remapping.h"
 #include "../iommu-pages.h"
@@ -3040,6 +3041,7 @@ static const struct iommu_dirty_ops amd_dirty_ops = {
 
 const struct iommu_ops amd_iommu_ops = {
 	.capable = amd_iommu_capable,
+	.hw_info = amd_iommufd_hw_info,
 	.blocked_domain = &blocked_domain,
 	.release_domain = &release_domain,
 	.identity_domain = &identity_domain.domain,
diff --git a/drivers/iommu/amd/iommufd.c b/drivers/iommu/amd/iommufd.c
new file mode 100644
index 000000000000..72eaaa923d04
--- /dev/null
+++ b/drivers/iommu/amd/iommufd.c
@@ -0,0 +1,31 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2025 Advanced Micro Devices, Inc.
+ */
+
+#include <linux/iommu.h>
+
+#include "iommufd.h"
+#include "amd_iommu.h"
+#include "amd_iommu_types.h"
+
+void *amd_iommufd_hw_info(struct device *dev, u32 *length, u32 *type)
+{
+	struct iommu_hw_info_amd *hwinfo;
+
+	if (*type != IOMMU_HW_INFO_TYPE_DEFAULT &&
+	    *type != IOMMU_HW_INFO_TYPE_AMD)
+		return ERR_PTR(-EOPNOTSUPP);
+
+	hwinfo = kzalloc(sizeof(*hwinfo), GFP_KERNEL);
+	if (!hwinfo)
+		return ERR_PTR(-ENOMEM);
+
+	*length = sizeof(*hwinfo);
+	*type = IOMMU_HW_INFO_TYPE_AMD;
+
+	hwinfo->efr = amd_iommu_efr;
+	hwinfo->efr2 = amd_iommu_efr2;
+
+	return hwinfo;
+}
diff --git a/drivers/iommu/amd/iommufd.h b/drivers/iommu/amd/iommufd.h
new file mode 100644
index 000000000000..8b726482778b
--- /dev/null
+++ b/drivers/iommu/amd/iommufd.h
@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2025 Advanced Micro Devices, Inc.
+ */
+
+#ifndef AMD_IOMMUFD_H
+#define AMD_IOMMUFD_H
+
+#if IS_ENABLED(CONFIG_IOMMUFD)
+void *amd_iommufd_hw_info(struct device *dev, u32 *length, u32 *type);
+#else
+#define amd_iommufd_hw_info NULL
+#endif
+
+#endif /* AMD_IOMMUFD_H */
diff --git a/include/uapi/linux/iommufd.h b/include/uapi/linux/iommufd.h
index c218c89e0e2e..efb52709c0a2 100644
--- a/include/uapi/linux/iommufd.h
+++ b/include/uapi/linux/iommufd.h
@@ -613,6 +613,32 @@ struct iommu_hw_info_tegra241_cmdqv {
 	__u8 __reserved;
 };
 
+/**
+ * struct iommu_hw_info_amd - AMD IOMMU device info
+ *
+ * @efr : Value of AMD IOMMU Extended Feature Register (EFR)
+ * @efr2: Value of AMD IOMMU Extended Feature 2 Register (EFR2)
+ *
+ * Please See description of these registers in the following sections of
+ * the AMD I/O Virtualization Technology (IOMMU) Specification.
+ * (https://docs.amd.com/v/u/en-US/48882_3.10_PUB)
+ *
+ * - MMIO Offset 0030h IOMMU Extended Feature Register
+ * - MMIO Offset 01A0h IOMMU Extended Feature 2 Register
+ *
+ * Note: The EFR and EFR2 are raw values reported by hardware.
+ * VMM is responsible to determine the appropriate flags to be exposed to
+ * the VM since cetertain features are not currently supported by the kernel
+ * for HW-vIOMMU.
+ *
+ * Current VMM-allowed list of feature flags are:
+ * - EFR[GTSup, GASup, GioSup, PPRSup, EPHSup, GATS, GLX, PASmax]
+ */
+struct iommu_hw_info_amd {
+	__aligned_u64 efr;
+	__aligned_u64 efr2;
+};
+
 /**
  * enum iommu_hw_info_type - IOMMU Hardware Info Types
  * @IOMMU_HW_INFO_TYPE_NONE: Output by the drivers that do not report hardware
@@ -622,6 +648,7 @@ struct iommu_hw_info_tegra241_cmdqv {
  * @IOMMU_HW_INFO_TYPE_ARM_SMMUV3: ARM SMMUv3 iommu info type
  * @IOMMU_HW_INFO_TYPE_TEGRA241_CMDQV: NVIDIA Tegra241 CMDQV (extension for ARM
  *                                     SMMUv3) info type
+ * @IOMMU_HW_INFO_TYPE_AMD: AMD IOMMU info type
  */
 enum iommu_hw_info_type {
 	IOMMU_HW_INFO_TYPE_NONE = 0,
@@ -629,6 +656,7 @@ enum iommu_hw_info_type {
 	IOMMU_HW_INFO_TYPE_INTEL_VTD = 1,
 	IOMMU_HW_INFO_TYPE_ARM_SMMUV3 = 2,
 	IOMMU_HW_INFO_TYPE_TEGRA241_CMDQV = 3,
+	IOMMU_HW_INFO_TYPE_AMD = 4,
 };
 
 /**
-- 
2.34.1

On Thu, Sep 04, 2025 at 07:31:12PM +0000, Suravee Suthikulpanit wrote:
> AMD IOMMU Extended Feature (EFR) and Extended Feature 2 (EFR2) registers
> specify features supported by each IOMMU hardware instance.
> The IOMMU driver checks each feature-specific bits before enabling
> each feature at run time.
> 
> For IOMMUFD, the hypervisor passes the raw value of amd_iommu_efr and
> amd_iommu_efr2 to VMM via iommufd IOMMU_DEVICE_GET_HW_INFO ioctl.
> 
> Reviewed-by: Nicolin Chen <nicolinc@nvidia.com>
> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
> ---
> Change in v4:
>  * Add CONFIG_AMD_IOMMU_IOMMUFD
>  * Update comment regarding EFR/EFR2 from struct iommu_hw_info_amd.
> 
> Change in v3:
>  * Remove extern
>  * Fix link to IOMMU spec
>  * Update kdoc
> 
> Change in v2:
>  * Do not mask the EFR/EFR2 and simply return the value reported by hardware
>  * Move amd_iommufd_hw_info() to drivers/iommu/amd/iommufd.c
>  * Also support IOMMU_HW_INFO_TYPE_DEFAULT
> 
>  drivers/iommu/amd/Kconfig    | 10 ++++++++++
>  drivers/iommu/amd/Makefile   |  1 +
>  drivers/iommu/amd/iommu.c    |  2 ++
>  drivers/iommu/amd/iommufd.c  | 31 +++++++++++++++++++++++++++++++
>  drivers/iommu/amd/iommufd.h  | 15 +++++++++++++++
>  include/uapi/linux/iommufd.h | 28 ++++++++++++++++++++++++++++
>  6 files changed, 87 insertions(+)
>  create mode 100644 drivers/iommu/amd/iommufd.c
>  create mode 100644 drivers/iommu/amd/iommufd.h

There was a kbuild issue so this needs to be resent, but

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

Jason

On 9/5/2025 1:01 AM, Suravee Suthikulpanit wrote:
> AMD IOMMU Extended Feature (EFR) and Extended Feature 2 (EFR2) registers
> specify features supported by each IOMMU hardware instance.
> The IOMMU driver checks each feature-specific bits before enabling
> each feature at run time.
> 
> For IOMMUFD, the hypervisor passes the raw value of amd_iommu_efr and
> amd_iommu_efr2 to VMM via iommufd IOMMU_DEVICE_GET_HW_INFO ioctl.
> 
> Reviewed-by: Nicolin Chen <nicolinc@nvidia.com>
> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
> ---

.../...

> diff --git a/drivers/iommu/amd/iommufd.c b/drivers/iommu/amd/iommufd.c
> new file mode 100644
> index 000000000000..72eaaa923d04
> --- /dev/null
> +++ b/drivers/iommu/amd/iommufd.c
> @@ -0,0 +1,31 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (C) 2025 Advanced Micro Devices, Inc.
> + */
> +
> +#include <linux/iommu.h>
> +
> +#include "iommufd.h"
> +#include "amd_iommu.h"
> +#include "amd_iommu_types.h"
> +
> +void *amd_iommufd_hw_info(struct device *dev, u32 *length, u32 *type)
> +{
> +	struct iommu_hw_info_amd *hwinfo;
> +
> +	if (*type != IOMMU_HW_INFO_TYPE_DEFAULT &&
> +	    *type != IOMMU_HW_INFO_TYPE_AMD)
> +		return ERR_PTR(-EOPNOTSUPP);
> +
> +	hwinfo = kzalloc(sizeof(*hwinfo), GFP_KERNEL);
> +	if (!hwinfo)
> +		return ERR_PTR(-ENOMEM);
> +
> +	*length = sizeof(*hwinfo);
> +	*type = IOMMU_HW_INFO_TYPE_AMD;
> +
> +	hwinfo->efr = amd_iommu_efr;
> +	hwinfo->efr2 = amd_iommu_efr2;
> +
> +	return hwinfo;
> +}
> diff --git a/drivers/iommu/amd/iommufd.h b/drivers/iommu/amd/iommufd.h
> new file mode 100644
> index 000000000000..8b726482778b
> --- /dev/null
> +++ b/drivers/iommu/amd/iommufd.h
> @@ -0,0 +1,15 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Copyright (C) 2025 Advanced Micro Devices, Inc.
> + */
> +
> +#ifndef AMD_IOMMUFD_H
> +#define AMD_IOMMUFD_H
> +
> +#if IS_ENABLED(CONFIG_IOMMUFD)

It should be `CONFIG_AMD_IOMMU_IOMMUFD`

Otherwise patch looks good to me.

Reviewed-by: Vasant Hegde <vasant.hegde@amd.com>

-Vasant

Hi Suravee,

kernel test robot noticed the following build errors:

[auto build test ERROR on linus/master]
[also build test ERROR on v6.17-rc5 next-20250908]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Suravee-Suthikulpanit/iommu-amd-Add-support-for-hw_info-for-iommu-capability-query/20250905-033352
base:   linus/master
patch link:    https://lore.kernel.org/r/20250904193112.7418-1-suravee.suthikulpanit%40amd.com
patch subject: [PATCH v4] iommu/amd: Add support for hw_info for iommu capability query
config: x86_64-rhel-9.4-func (https://download.01.org/0day-ci/archive/20250909/202509090900.HNQfwn5v-lkp@intel.com/config)
compiler: gcc-14 (Debian 14.2.0-19) 14.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250909/202509090900.HNQfwn5v-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202509090900.HNQfwn5v-lkp@intel.com/

All errors (new ones prefixed by >>):

>> ld: drivers/iommu/amd/iommu.o:(.rodata+0x25a8): undefined reference to `amd_iommufd_hw_info'

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki