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

[Baolu Lu <baolu.lu@linux.intel.com>]

On 6/24/25 16:12, Tian, Kevin wrote:
>> From: Baolu Lu <baolu.lu@linux.intel.com>
>> 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.

Okay, make sense.