Re: [PATCH RFC v3 02/12] iommu: Add a flag to indicate immutable singleton group

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

On 2022/4/12 15:39, Tian, Kevin wrote:
>> From: Lu Baolu <baolu.lu@linux.intel.com>
>> Sent: Sunday, April 10, 2022 6:25 PM
>> @@ -898,6 +941,20 @@ int iommu_group_add_device(struct iommu_group
>> *group, struct device *dev)
>>   	list_add_tail(&device->list, &group->devices);
>>   	if (group->domain  && !iommu_is_attach_deferred(dev))
>>   		ret = __iommu_attach_device(group->domain, dev);
>> +
>> +	/*
>> +	 * Use standard PCI bus topology, isolation features, and DMA
>> +	 * alias quirks to set the immutable singleton attribute. If
>> +	 * the device came from DT, assume it is static and then
>> +	 * singleton can know from the device count in the group.
>> +	 */
>> +	if (dev_is_pci(dev))
>> +		group->immutable_singleton =
>> +				pci_immutably_isolated(to_pci_dev(dev));
>> +	else if (is_of_node(dev_fwnode(dev)))
>> +		group->immutable_singleton =
>> +				(iommu_group_device_count(group) == 1);
>> +
> 
> btw probably we also want to check when a 2nd device is added
> to a group marked as singleton, just in case some weird thing happens?

It depends on how we judge whether the group to which a DT device
belongs is a singleton. As I explained in another thread, current trick
doesn't support doing this.

Best regards,
baolu