Re: [PATCH V4] PCI: Extend ACS configurability

[Jason Gunthorpe <jgg@nvidia.com>]

On Wed, Jun 26, 2024 at 07:40:31AM +0000, Tian, Kevin wrote:
> > From: Vidya Sagar <vidyas@nvidia.com>
> > 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