Re: [PATCH 0/2] iommu: Make pasid array per device

From: Jason Gunthorpe
Date: Wed Aug 02 2023 - 10:15:41 EST

On Tue, Aug 01, 2023 at 02:31:23PM +0800, Lu Baolu wrote:
> The PCI PASID enabling interface guarantees that the address space used
> by each PASID is unique. This is achieved by checking that the PCI ACS
> path is enabled for the device. If the path is not enabled, then the
> PASID feature cannot be used.
> if (!pci_acs_path_enabled(pdev, NULL, PCI_ACS_RR | PCI_ACS_UF))
> return -EINVAL;
> The PASID array is not an attribute of the IOMMU group. It is more
> natural to store the PASID array in the per-device IOMMU data. This
> makes the code clearer and easier to understand. No functional changes
> are intended.

Is there a reason to do this?

*PCI* requires the ACS/etc because PCI kind of messed up how switches
handled PASID so PASID doesn't work otherwise.

But there is nothing that says other bus type can't have working
(non-PCI) PASID and still have device isolation issues.

So unless there is a really strong reason to do this we should keep
the PASID list in the group just like the domain.