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

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Message-ID: <BN9PR11MB5276CD6BD2C2832533304CE78C78A@BN9PR11MB5276.namprd11.prod.outlook.com>
Date: Tue, 24 Jun 2025 08:28:43 +0000
From: "Tian, Kevin" <kevin.tian@...el.com>
To: Xu Yilun <yilun.xu@...ux.intel.com>, Baolu Lu <baolu.lu@...ux.intel.com>
CC: "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>, "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: Xu Yilun <yilun.xu@...ux.intel.com>
> Sent: Tuesday, June 24, 2025 4:12 PM
> 
> On Tue, Jun 24, 2025 at 11:32:01AM +0800, Baolu Lu wrote:
> > 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
> 
> Yes, I got this idea from here.
> 
> https://lore.kernel.org/all/20250604132403.GJ5028@nvidia.com/
> 
> > 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?
> 
> Mm.. I don't have a clear idea how SIOV assignment work with iommufd,
> may come back later.
> 

Let's put SIOV out of scope here. It's not supported yet. there are
other obstacles to be figured out (e.g. igroup etc.) when it comes to
the table.