linux-kernel - RE: [PATCH v5 00/13] iommufd: Add vIOMMU infrastructure (Part-2: vDEVICE)

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Message-ID: <BL1PR11MB527135D53410D86949F39FEB8C4B2@BL1PR11MB5271.namprd11.prod.outlook.com>
Date: Tue, 29 Oct 2024 08:51:21 +0000
From: "Tian, Kevin" <kevin.tian@...el.com>
To: Jason Gunthorpe <jgg@...dia.com>
CC: Nicolin Chen <nicolinc@...dia.com>, "will@...nel.org" <will@...nel.org>,
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Subject: RE: [PATCH v5 00/13] iommufd: Add vIOMMU infrastructure (Part-2:
 vDEVICE)

> From: Jason Gunthorpe <jgg@...dia.com>
> Sent: Monday, October 28, 2024 10:17 PM
> 
> > > to
> > > a Context Table. This virt_id helps IOMMU drivers to link the vID to a pID
> > > of the device against the physical IOMMU instance. This is essential for a
> > > vIOMMU-based invalidation, where the request contains a device's vID
> for a
> > > device cache flush, e.g. ATC invalidation.
> >
> > probably connect this to vCMDQ passthrough? otherwise for sw-based
> > invalidation the userspace can always replace vID with pID before
> > submitting the request.
> 
> You can't just do that, the ID in the invalidation command has to be
> validated by the kernel.

sure the ID must be validated to match the iommufd_device but not
exactly going through a vID indirectly.

> 
> At that point you may as well just use the vID instead of inventing a
> new means to validate raw pIDs.

w/o VCMDQ stuff validating raw pID sounds the natural way while
vID is more like a new means and not mandatory.

I'm fine with this design but just didn't feel the above description
is accurate.