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Re: [Xen-devel] Implementing mem-access for PV guests

At 10:48 -0400 on 25 Apr (1366886887), Andres Lagar-Cavilla wrote:
> > 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,
> wouldn't intercepting all calls to get_page_from_gfn ought to cover
> it?

I doubt it -- in the PV code, an MFN is and MFN and needs no
translation; get_page_from_gfn() &c are only called from code that's
common to both PV and HVM.


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