Re: [PATCH v6 03/24] iommu/amd: Detect and initialize AMD vIOMMU feature

[Vasant Hegde <vasant.hegde@amd.com>]

On 9/30/2026 2:53 PM, Suravee Suthikulpanit wrote:
> 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.

Nit: This is redundant statement. No need to have above line.

> + * 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) {

Please add a additional check to skip vIOMMU if amd_iommu_snp_en is true.
Support w/ SNP needs PSP plumbing and not part of this series.

-Vasant