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

On 7/24/2026 8:45 PM, Jason Gunthorpe wrote:
> 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?

Right. I didn't realized core has this check. I will drop this check in next
version.

> 
>> -	/*
>> -	 * 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?


I did consider dropping these two checks, but I was not entirely sure. So I kept
as is for now. Once these series settles and I can go with next step of dropping
these two checks.

@Alex, @Mario, Any suggestions ?

-Vasant

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