Re: [PATCH] iommu/amd: Add support for HTRangeIgnore feature

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

On 3/17/2025 11:20 AM, Sairaj Kodilkar wrote:
> AMD IOMMU reserves the address range 0xfd00000000-0xffffffffff for
> the hypertransport protocol (HT) and has special meaning. Hence devices
> cannot use this address range for the DMA. However on some AMD platforms
> this HT range is shifted to the very top of the address space and new
> feature bit `HTRangeIgnore` is introduced. When this feature bit is on,
> IOMMU treats the GPA access to the legacy HT range as regular GPA access.
> 
> Signed-off-by: Sairaj Kodilkar <sarunkod@amd.com>

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

-Vasant

> ---
>  drivers/iommu/amd/amd_iommu.h       | 2 ++
>  drivers/iommu/amd/amd_iommu_types.h | 1 +
>  drivers/iommu/amd/init.c            | 5 +++++
>  drivers/iommu/amd/iommu.c           | 3 +++
>  4 files changed, 11 insertions(+)
> 
> diff --git a/drivers/iommu/amd/amd_iommu.h b/drivers/iommu/amd/amd_iommu.h
> index 68debf5ee2d7..156eb66caca1 100644
> --- a/drivers/iommu/amd/amd_iommu.h
> +++ b/drivers/iommu/amd/amd_iommu.h
> @@ -148,6 +148,8 @@ static inline int get_pci_sbdf_id(struct pci_dev *pdev)
>  	return PCI_SEG_DEVID_TO_SBDF(seg, devid);
>  }
>  
> +bool amd_iommu_ht_range_ignore(void);
> +
>  /*
>   * This must be called after device probe completes. During probe
>   * use rlookup_amd_iommu() get the iommu.
> diff --git a/drivers/iommu/amd/amd_iommu_types.h b/drivers/iommu/amd/amd_iommu_types.h
> index 23caea22f8dc..1b3fc25bcdbf 100644
> --- a/drivers/iommu/amd/amd_iommu_types.h
> +++ b/drivers/iommu/amd/amd_iommu_types.h
> @@ -111,6 +111,7 @@
>  #define FEATURE_SNPAVICSUP	GENMASK_ULL(7, 5)
>  #define FEATURE_SNPAVICSUP_GAM(x) \
>  	(FIELD_GET(FEATURE_SNPAVICSUP, x) == 0x1)
> +#define FEATURE_HT_RANGE_IGNORE		BIT_ULL(11)
>  
>  /* Note:
>   * The current driver only support 16-bit PASID.
> diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
> index cb536d372b12..538af5a7418f 100644
> --- a/drivers/iommu/amd/init.c
> +++ b/drivers/iommu/amd/init.c
> @@ -258,6 +258,11 @@ int amd_iommu_get_num_iommus(void)
>  	return amd_iommus_present;
>  }
>  
> +bool amd_iommu_ht_range_ignore(void)
> +{
> +	return check_feature2(FEATURE_HT_RANGE_IGNORE);
> +}
> +
>  /*
>   * Iterate through all the IOMMUs to get common EFR
>   * masks among all IOMMUs and warn if found inconsistency.
> diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
> index cd5116d8c3b2..4985855914a3 100644
> --- a/drivers/iommu/amd/iommu.c
> +++ b/drivers/iommu/amd/iommu.c
> @@ -2907,6 +2907,9 @@ static void amd_iommu_get_resv_regions(struct device *dev,
>  		return;
>  	list_add_tail(&region->list, head);
>  
> +	if (amd_iommu_ht_range_ignore())
> +		return;
> +
>  	region = iommu_alloc_resv_region(HT_RANGE_START,
>  					 HT_RANGE_END - HT_RANGE_START + 1,
>  					 0, IOMMU_RESV_RESERVED, GFP_KERNEL);