Re: Proposal for physical address based hypercalls

[Juergen Gross <jgross@xxxxxxxx>]

On 29.09.22 14:58, Jan Beulich wrote:
> On 29.09.2022 14:26, Juergen Gross wrote:
> > On 29.09.22 13:32, Jan Beulich wrote:
> > > Finally - in how far are we concerned of PV guests using linear
> > > addresses for hypercall buffers? I ask because I don't think the model
> > > lends itself to use also for the PV guest interfaces.
> > Good question.
> >
> > As long as we support PV guests we can't drop support for linear addresses
> > IMO. So the question is whether we are fine with PV guests not using the
> > pre-registered buffers, or if we want to introduce an interface for PV
> > guests using GFNs instead of MFNs.
> GFN == MFN for PV, and using PFN space (being entirely controlled by the
Sigh. I meant to write PFNs, of course.

> guest) doesn't look attractive either. Plus any form of translation we'd
> need to do for PV would involve getting and putting page references (for
> writes also type references), along the lines of what is already
> happening for HVM. Since "put" may involve freeing a page, which in turn
> require locks to be taken, we'd need to carefully check that no such
> translation can occur from an inappropriate call chain.
Sounds like a good reason to continue using linear addresses then.


Juergen

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