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

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Message-ID: <99cb0f7a-0d21-4071-844d-893b230b7038@amd.com>
Date: Sat, 8 Nov 2025 23:09:51 +0530
From: Vasant Hegde <vasant.hegde@....com>
To: Suravee Suthikulpanit <suravee.suthikulpanit@....com>, jgg@...dia.com,
 nicolinc@...dia.com
Cc: linux-kernel@...r.kernel.org, robin.murphy@....com, will@...nel.org,
 joro@...tes.org, kevin.tian@...el.com, jsnitsel@...hat.com,
 iommu@...ts.linux.dev, santosh.shukla@....com, sairaj.arunkodilkar@....com,
 jon.grimm@....com, prashanthpra@...gle.com, wvw@...gle.com,
 wnliu@...gle.com, gptran@...gle.com, kpsingh@...gle.com,
 joao.m.martins@...cle.com, alejandro.j.jimenez@...cle.com
Subject: Re: [PATCH v4 09/16] iommu/amd: Always enable GCR3TRPMode when
 supported.

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@...dia.com>
> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
> ---
>  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