Re: [RFC v2] /dev/iommu uAPI proposal

Jason Gunthorpe
2021-08-05T11:27:21Z

On Wed, Aug 04, 2021 at 10:59:21PM +0000, Tian, Kevin wrote:
> > From: Jason Gunthorpe <jgg@nvidia.com>
> > Sent: Wednesday, August 4, 2021 10:05 PM
> >
> > On Mon, Aug 02, 2021 at 02:49:44AM +0000, Tian, Kevin wrote:
> >
> > > Can you elaborate? IMO the user only cares about the label (device cookie
> > > plus optional vPASID) which is generated by itself when doing the attaching
> > > call, and expects this virtual label being used in various spots (invalidation,
> > > page fault, etc.). How the system labels the traffic (the physical RID or RID+
> > > PASID) should be completely invisible to userspace.
> >
> > I don't think that is true if the vIOMMU driver is also emulating
> > PASID. Presumably the same is true for other PASID-like schemes.
> >
>
> I'm getting even more confused with this comment. Isn't it the
> consensus from day one that physical PASID should not be exposed
> to userspace as doing so breaks live migration?

Uh, no?

> with PASID emulation vIOMMU only cares about vPASID instead of
> pPASID, and the uAPI only requires user to register vPASID instead
> of reporting pPASID back to userspace...

vPASID is only a feature of one device in existance, so we can't make
vPASID mandatory.

Jason