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

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Message-ID: <BN9PR11MB52763649BE32A38A60866D518C78A@BN9PR11MB5276.namprd11.prod.outlook.com>
Date: Tue, 24 Jun 2025 08:12:14 +0000
From: "Tian, Kevin" <kevin.tian@...el.com>
To: Baolu Lu <baolu.lu@...ux.intel.com>, Xu Yilun <yilun.xu@...ux.intel.com>,
	"jgg@...dia.com" <jgg@...dia.com>, "jgg@...pe.ca" <jgg@...pe.ca>,
	"will@...nel.org" <will@...nel.org>, "aneesh.kumar@...nel.org"
	<aneesh.kumar@...nel.org>
CC: "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"joro@...tes.org" <joro@...tes.org>, "robin.murphy@....com"
	<robin.murphy@....com>, "shuah@...nel.org" <shuah@...nel.org>,
	"nicolinc@...dia.com" <nicolinc@...dia.com>, "aik@....com" <aik@....com>,
	"Williams, Dan J" <dan.j.williams@...el.com>, "Xu, Yilun"
	<yilun.xu@...el.com>
Subject: RE: [PATCH v2 3/4] iommufd: Destroy vdevice on idevice destroy

> From: Baolu Lu <baolu.lu@...ux.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.