Re: [PATCH v8 12/15] iommufd/viommu: Allow PCI TSM backends to provide vIOMMU operations

[Jason Gunthorpe <jgg@ziepe.ca>]

On Fri, Nov 06, 2026 at 08:03:48AM +0000, Tian, Kevin wrote:
> > From: Jacob Pan <jacob.pan@linux.microsoft.com>
> > Sent: Friday, November 6, 2026 1:16 AM
> > 
> > Hi Jason,
> > 
> > On Wed, 4 Nov 2026 20:49:34 -0400
> > Jason Gunthorpe <jgg@ziepe.ca> wrote:
> > 
> > > On Wed, Nov 04, 2026 at 03:23:51PM -0800, Jacob Pan wrote:
> > >
> > > > I am thinking MSHV/pKVM can register an assignment-only tsm_dev to
> > > > leverage this? Could PCI/TSM support this role without
> > > > device-security?
> > >
> > > It is certainly not what TSM was originally imagined for, but with our
> > > new arrangement, yah maybe so?
> > I will rebase on this set and send out patches for a detailed review.
> > 
> > > TSM basically just becomes this weird overlay driver on the PCI device
> > > that does stuff. Some of the stuff it might do:
> > >  - Register an attestation subsystem device to do SPDM
> > >  - Register to allow iommufd to create a viommu
> > >  - Some status sysfs ?
> > >  - ??
> > >
> > So we may expand pci tsm to have more than one role? currently it has
> > one.
> > int pci_tsm_register(struct tsm_dev *tsm_dev) {
> > ...
> > 	roles = is_link_tsm(tsm_dev) + is_devsec_tsm(tsm_dev) +
> > 		is_assignment_tsm(tsm_dev);
> > 	if (roles != 1)
> > 		return -EINVAL;
> 
> Not sure what'd be a proper name for this, but it sounds to me that
> it tries to over-abstract something into tsm. The reused logic related
> to assignment or viommu is relatively small, so the other option below
> sounds better if it can work.
> 
> Or it may be the original provider framework that Aneesh proposed,
> so tsm/MSHV/pKVM can each register its own backend...

That is definately undesirable for TSM

I think the very best answer for this is to get the viommu from the
"kvm" fd, I just don't quite know how you implement it..

Maybe just register something like a notifier chain where the struct
file * and the viommu type value goes in and a viommu object comes
back out?

Jason