Re: [PATCH v4 09/16] iommu/amd: Always enable GCR3TRPMode when supported.

[Vasant Hegde]

On 10/21/2025 7:13 AM, Suravee Suthikulpanit wrote:
> The GCR3TRPMode feature allows the DTE[GCR3TRP] field to be configured
> with GPA (instead of SPA). This simplifies the implementation, and is
> a pre-requisite for nested translation support.
> 
> Therefore, always enable this feature if available.
> 
> Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
> ---
>  drivers/iommu/amd/amd_iommu_types.h | 1 +
>  drivers/iommu/amd/init.c            | 3 +++
>  2 files changed, 4 insertions(+)
> 
> diff --git a/drivers/iommu/amd/amd_iommu_types.h b/drivers/iommu/amd/amd_iommu_types.h
> index 556f1df32d53..9226edd8af69 100644
> --- a/drivers/iommu/amd/amd_iommu_types.h
> +++ b/drivers/iommu/amd/amd_iommu_types.h
> @@ -185,6 +185,7 @@
>  #define CONTROL_EPH_EN		45
>  #define CONTROL_XT_EN		50
>  #define CONTROL_INTCAPXT_EN	51
> +#define CONTROL_GCR3TRPMODE	58
>  #define CONTROL_IRTCACHEDIS	59
>  #define CONTROL_SNPAVIC_EN	61
>  
> diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
> index f2991c11867c..c45a4bd89569 100644
> --- a/drivers/iommu/amd/init.c
> +++ b/drivers/iommu/amd/init.c
> @@ -1122,6 +1122,9 @@ static void iommu_enable_gt(struct amd_iommu *iommu)
>  		return;
>  
>  	iommu_feature_enable(iommu, CONTROL_GT_EN);
> +
> +	if (check_feature2(FEATURE_GCR3TRPMODE))
> +		iommu_feature_enable(iommu, CONTROL_GCR3TRPMODE);

This works for now as iommu_snp_enable() enable is getting called later.
But how about moving it to iommu_init_flags() ? Also we should probably add a
comment here.


Not for this series, but may be we should rename FEATURE -> FEATURE2 so that its
clear that these are coming from EFR2 register.

-Vasant