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

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Message-ID: <a2fddab4-bc85-46f6-9008-57a26e099698@linux.intel.com>
Date: Tue, 24 Jun 2025 11:32:01 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: Xu Yilun <yilun.xu@...ux.intel.com>, jgg@...dia.com, jgg@...pe.ca,
 kevin.tian@...el.com, will@...nel.org, aneesh.kumar@...nel.org
Cc: iommu@...ts.linux.dev, linux-kernel@...r.kernel.org, joro@...tes.org,
 robin.murphy@....com, shuah@...nel.org, nicolinc@...dia.com, aik@....com,
 dan.j.williams@...el.com, yilun.xu@...el.com
Subject: Re: [PATCH v2 3/4] iommufd: Destroy vdevice on idevice destroy

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?

Thanks,
baolu