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

[Tian, Kevin]

> From: Jason Gunthorpe <jgg@xxxxxxxx>
> Sent: Thursday, August 3, 2023 11:19 PM
> 
> On Thu, Aug 03, 2023 at 12:44:03AM +0000, Tian, Kevin wrote:
> > > From: Jason Gunthorpe <jgg@xxxxxxxx>
> > > Sent: Wednesday, August 2, 2023 10:16 PM
> > >
> > > 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.
> > >
> >
> > this comes from the consensus in [1].
> >
> > [1] https://lore.kernel.org/linux-iommu/ZAcyEzN4102gPsWC@xxxxxxxxxx/
> 
> That consensus was that we don't have PASID support if there is
> multi-device groups, at least in iommufd.. That makes sense. If we
> want to change the core code to enforce this that also makes sense
> 
> But this series is just moving the array?
> 

This is a preparation series for supporting PASID in iommufd (will be
sent out probably after next version of the nesting series).

It only moves the array by taking only PCI into consideration. We could
add an explicit enforcement in iommu core for all types of devices.