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

[Tian, Kevin]

> From: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> 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?