Re: [PATCH 2/2] iommu/amd: Force identity mode for selected GPUs only

[Jason Gunthorpe <jgg@ziepe.ca>]

On Thu, Jul 23, 2026 at 06:15:48AM +0000, Vasant Hegde wrote:
> @@ -3120,20 +3146,28 @@ static int amd_iommu_def_domain_type(struct device *dev)
>  	if (!dev_data)
>  		return 0;
>  
> +	if (!dev_is_pci(dev))
> +		return 0;
> +
>  	/* Always use DMA domain for untrusted device */
> -	if (dev_is_pci(dev) && to_pci_dev(dev)->untrusted)
> +	if (to_pci_dev(dev)->untrusted)
>  		return IOMMU_DOMAIN_DMA;

The core code does this, it shouldn't be in a driver?

> -	/*
> -	 * Do not identity map IOMMUv2 capable devices when:
> -	 *  - memory encryption is active, because some of those devices
> -	 *    (AMD GPUs) don't have the encryption bit in their DMA-mask
> -	 *    and require remapping.
> -	 *  - SNP is enabled, because it prohibits DTE[Mode]=0.
> -	 */
> -	if (pdev_pasid_supported(dev_data) &&
> -	    !cc_platform_has(CC_ATTR_MEM_ENCRYPT) &&
> -	    !amd_iommu_snp_en) {
> +	/* Apply device specific quirks */
> +	if (quirks_force_identity_mapping(to_pci_dev(dev))) {
> +
> +		/*
> +		 * When memory encryption is active, some of these devices
> +		 * don't have the encryption bit in their DMA-mask and
> +		 * require remapping.
> +		 */
> +		if (cc_platform_has(CC_ATTR_MEM_ENCRYPT))
> +			return 0;

I think this can probably be dropped now? There is no intersection of
this old broken embedded GPU and a CPU that supports CC right?

> +
> +		/* DTE[Mode]=0 is prohibited when SNP is enabled */
> +		if (amd_iommu_snp_en)
> +			return 0;

Ditto?

Jason