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

[Mario Limonciello <mario.limonciello@amd.com>]

On 7/26/26 23:19, Vasant Hegde wrote:
> 
> 
> 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 ?
> 

The background comes from this series:

https://lore.kernel.org/all/20200824105415.21000-1-joro@8bytes.org/

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