RE: [PATCH V4] PCI: Extend ACS configurability

[Tian, Kevin]

> From: Vidya Sagar <vidyas@xxxxxxxxxx>
> Sent: Tuesday, June 25, 2024 11:32 PM
> 
> PCIe ACS settings control the level of isolation and the possible P2P
> paths between devices. With greater isolation the kernel will create
> smaller iommu_groups and with less isolation there is more HW that
> can achieve P2P transfers. From a virtualization perspective all
> devices in the same iommu_group must be assigned to the same VM as
> they lack security isolation.
> 

It'll be helpful to also call out the impact of losing other features (e.g. PASID)
with less isolation:

pci_enable_pasid()
{
	...
	if (!pci_acs_path_enabled(pdev, NULL, PCI_ACS_RR | PCI_ACS_UF))
		return -EINVAL;
	...
}