Re: [PATCH v10 04/12] iommu: Add attach/detach_dev_pasid iommu interface

[Baolu Lu <baolu.lu@linux.intel.com>]

On 2022/7/29 10:56, Tian, Kevin wrote:
>> +static bool iommu_group_device_pasid_viable(struct iommu_group *group,
>> +					    struct device *dev)
>> +{
>> +	int count;
>> +
>> +	count = iommu_group_device_count(group);
>> +	if (count != 1)
>> +		return false;
>> +
>> +	/*
>> +	 * Block PASID attachment in cases where the PCI fabric is
>> +	 * routing based on address. PCI/ACS disables that.
>> +	 */
>> +	if (dev_is_pci(dev))
>> +		return pci_acs_path_enabled(to_pci_dev(dev), NULL,
>> +					    REQ_ACS_FLAGS);
> I think we are leaning toward doing above check in pci_enable_pasid().
> Then no singleton check inside iommu core.

The iommu grouping also considers other things, like PCI alias. There
are many calls of pci_add_dma_alias() in drivers/pci/quirks.c.
Therefore, I believe that pci_acs_path_enabled() returning true doesn't
guarantees a singleton group.

> 
> Presumably similar check can be done in DT/ACPI path of enabling pasid?
> 

I can't find the pasid (or anything similar) enabling interfaces for
DT or ACPI. They are device specific?

Best regards,
baolu