RE: [RFC PATCH v6 08/11] iommufd: Add vIOMMU provider support

[Tian, Kevin]

> From: Jason Gunthorpe <jgg@xxxxxxxxxx>
> Sent: Friday, September 25, 2026 8:39 PM
> 
> On Fri, Sep 25, 2026 at 11:38:15AM +0530, Aneesh Kumar K.V wrote:
> > Jason Gunthorpe <jgg@xxxxxxxxxx> writes:
> >
> > >> vIOMMU creation currently dispatches directly through the physical
> IOMMU
> > >> driver. Some vIOMMU types need an implementation supplied by another
> > >> subsystem, together with private data whose lifetime extends across all
> > >> vIOMMUs using that implementation.
> > >>
> > >> Introduce a vIOMMU provider that associates implementation operations,
> > >> their module owner and private data. Allow one external provider to
> > >> register for each non-default vIOMMU type.
> > >
> > > This seems much more extensive than I imagined when I proposed this.
> > >
> > > I imagined you'd just have iommufd see there is a TSM attached the pci
> > > device with a function call, and check if that TSM handled the
> > > requested iommu ID.
> > >
> > > No need for a registration system because we already know the only
> > > possible TSM driver that can handle it,
> > >
> >
> > Agreed, there will be only one vIOMMU provider. But, without a
> > registration mechanism, what would the module dependency look like?
> >
> > I currently have the TSM driver depending on IOMMUFD. Therefore, the TSM
> > driver needs to tell iommufd which vIOMMU type it provides and register
> > the corresponding provider. IOMMUFD does not call into TSM directly.
> 
> Just put the two new ops in:
> 
> struct pci_tsm_ops {
> 	size_t (*viommu_get_size)(struct device *dev, enum
> iommu_viommu_type type);
> 	int (*viommu_init)(struct iommufd_viommu *viommu, struct device
> *dev,
> 		    struct iommu_domain *parent,
> 		    const struct iommu_user_data *user_data);
> }
> 
> And bounce them with a static inline
> 
> static inline
> ssize_t pci_tsm_viommu_get_size(struct device *dev, enum
> iommu_viommu_type type)
> {
> 	const struct pci_tsm_ops *ops;
> 	struct pci_dev *pdev;
> 
> 	if (!dev_is_pci(dev))
> 		return -EINVAL;
> 
> 	pdev = to_pci_dev(dev);
> 	if (!pdev->tsm)
> 		return -ENODEV;
> 
> 	ops = to_pci_tsm_ops(pdev->tsm);
> 	if (!ops->viommu_get_size)
> 		return 0;
> 	return ops->viommu_get_size(dev, type);
> }
> 
> No module dependency.
> 
> The iommufd side is simple, it just calls this before calling the
> iommu driver. First one to return a size wins and creates the viommu.
> 
> We'd want to have a reasonable lifetime model where the the pdev->tsm
> is guarenteed stable while a driver is bound.
> 

+1