Re: Shouldn't VFIO virtualize the ATS capability?

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On Wed, 9 Nov 2016 14:49:02 +0000
Ilya Lesokhin <ilyal@xxxxxxxxxxxx> wrote:

> I would virtualize the "ATS Control Register".

And do what?

> Regarding poor behavior, I couldn't really find what happens when ATS is misconfigured, but I would assume it can cause problems.
> The scenarios I'm concerned about are:
> 	1. The guest enables translation caching, while the hypervisor thinks there are disabled -> Hypervisor won't issue invalidations.

Aren't invalidations issued by the iommu, why does the hypervisor need
to participate?  How would a software entity induce an invalidation?

> 	2. Smallest Translation Unit misconfiguration. Not sure if it will cause invalid access or only poor caching behavior.
> 
> Thanks,
> Ilya
> 
> > -----Original Message-----
> > From: Alex Williamson [mailto:alex.williamson@xxxxxxxxxx]
> > Sent: Sunday, November 06, 2016 7:09 PM
> > To: Ilya Lesokhin <ilyal@xxxxxxxxxxxx>
> > Cc: linux-pci@xxxxxxxxxxxxxxx; kvm@xxxxxxxxxxxxxxx; bhelgaas@xxxxxxxxxx
> > Subject: Re: Shouldn't VFIO virtualize the ATS capability?
> > 
> > On Sun, 6 Nov 2016 11:13:09 +0000
> > Ilya Lesokhin <ilyal@xxxxxxxxxxxx> wrote:
> >   
> > > Hi
> > > I've noticed that VFIO doesn't virtualize the ATS capability.
> > > It seems to me that translation caching and Smallest Translation Unit is  
> > something you would want to control on the host. Am I wrong?
> > 
> > What about those fields would we virtualize?  Why does the host need to be
> > an intermediary?  Can the user induce poor behavior with direct access to
> > them?  Thanks,
> > 
> > Alex  

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