Re: [PATCH V4] PCI: Extend ACS configurability

On Wed, Jun 26, 2024 at 07:40:31AM +0000, Tian, Kevin wrote:

quoted

From: Vidya Sagar <redacted>
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;
	...
}

Yeah, that is one of the considerations that might go into using
asymmetric ACS..

Jason