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

[Tim Deegan <tim@xxxxxxx>]

Please don't top-post.

At 12:31 -0400 on 25 Apr (1366893074), Andres Lagar-Cavilla wrote:
> Not disputing you need shadows.

What I was trying to say is, there are probably PV-only paths that don't
use get_page_from_gfn().  Or at least you'd have to audit the code
looking for them if you wanted to hook for mem-access there. 

Tim.

> Andres
> On Apr 25, 2013 11:40 AM, "Tim Deegan" <tim@xxxxxxx> wrote:
> 
> > 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.
> >
> > Tim.
> >

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel