Re: Implementing mem-access for PV guests

[Tim Deegan <tim@xen.org>]

At 01:02 +0000 on 25 Apr (1366851740), Aravindh Puthiyaparambil (aravindp) wrote:
> > > I'm finally to a point where I can start looking at this more closely.
> > > I'm trying to wrap my head around the shadow code to figure out the
> > > right course of action.
> > >
> > > I'd want HVMOP_set_mem_access to work with both shadow and EPT, so
> 
> Getting this to work with shadow would allow non-NPT HVM guests to
> have mem_access support or will this also extend to PV guests?

It could extend to PV guests as long as you're willing to run them on
shadow pagetables (i.e. with a significant performance hit).

> I am interested in getting this to work for PV guests so I was
> wondering how much extra work that would be. I can definitely help out
> with this effort.

I think you'd have to take a good look at the hypercall interface -- PV
guests have more ways of causing the hypervisor to read and write memory
for them (e.g. the MMU ops) which wouldn't be intercepted by shadow PTs.
It certainly ought to be possible, though.

Tim.