RE: [RFC v3 1/8] vfio: Add VFIO_IOMMU_PASID_REQUEST(alloc/free)

[Liu, Yi L]

> From: Liu, Yi L <yi.l.liu@xxxxxxxxx>
> Sent: Friday, January 31, 2020 8:41 PM
> To: Alex Williamson <alex.williamson@xxxxxxxxxx>
> Subject: RE: [RFC v3 1/8] vfio: Add VFIO_IOMMU_PASID_REQUEST(alloc/free)
> > > +static int vfio_iommu_type1_pasid_free(struct vfio_iommu *iommu,
> > > +				       unsigned int pasid)
> > > +{
> > > +	struct vfio_mm *vmm = iommu->vmm;
> > > +	int ret = 0;
> > > +
> > > +	mutex_lock(&iommu->lock);
> > > +	if (!IS_IOMMU_CAP_DOMAIN_IN_CONTAINER(iommu)) {
> >
> > But we could have been IOMMU backed when the pasid was allocated, did we
> just
> > leak something?  In fact, I didn't spot anything in this series that handles
> > a container with pasids allocated losing iommu backing.
> > I'd think we want to release all pasids when that happens since permission for
> > the user to hold pasids goes along with having an iommu backed device.
> 
> oh, yes. If a container lose iommu backend, then needs to reclaim the allocated
> PASIDs. right? I'll add it. :-)

Hi Alex,

I went through the flow again. Maybe current series has already covered
it. There is vfio_mm which is used to track allocated PASIDs. Its life
cycle is type1 driver open and release. If I understand it correctly,
type1 driver release happens when there is no more iommu backed groups
in a container.

static void __vfio_group_unset_container(struct vfio_group *group)
{
[...]

	/* Detaching the last group deprivileges a container, remove iommu */
	if (driver && list_empty(&container->group_list)) {
		driver->ops->release(container->iommu_data);
		module_put(driver->ops->owner);
		container->iommu_driver = NULL;
		container->iommu_data = NULL;
	}
[...]
}

Regards,
Yi Liu