RE: [PATCH v2 3/4] iommufd: Destroy vdevice on idevice destroy

[Tian, Kevin]

> From: Baolu Lu <baolu.lu@xxxxxxxxxxxxxxx>
> Sent: Tuesday, June 24, 2025 11:32 AM
> 
> On 6/23/25 17:49, Xu Yilun wrote:
> > Destroy iommufd_vdevice(vdev) on iommufd_idevice(idev) destroy so that
> > vdev can't outlive idev.
> >
> > iommufd_device(idev) represents the physical device bound to iommufd,
> > while the iommufd_vdevice(vdev) represents the virtual instance of the
> > physical device in the VM. The lifecycle of the vdev should not be
> > longer than idev. This doesn't cause real problem on existing use cases
> > cause vdev doesn't impact the physical device, only provides
> > virtualization information. But to extend vdev for Confidential
> > Computing(CC), there are needs to do secure configuration for the vdev,
> > e.g. TSM Bind/Unbind. These configurations should be rolled back on idev
> > destroy, or the external driver(VFIO) functionality may be impact.
> >
> > Building the association between idev & vdev requires the two objects
> > pointing each other, but not referencing each other.
> 
> Does this mean each idevice can have at most a single vdevice? Is it
> possible that different PASIDs of a physical device are assigned to
> userspace for different purposes, such that there is a need for multiple
> vdevices per idevice?
> 

PASID is a resource of physical device. If it's reported to a VM then
it becomes the resource of virtual device. 1:1 association makes
sense here.