Re: [Xen-devel] [PATCH v1 3/8]: PVH startup changes (enlighten.c)

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2012-10-03 at 23:37 +0100, Mukesh Rathor wrote:
> On Wed, 3 Oct 2012 12:58:22 +0100
> Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx> wrote:
> 
> > On Wed, 3 Oct 2012, Mukesh Rathor wrote:
> > > On Tue, 2 Oct 2012 18:36:19 -0700
> > > Mukesh Rathor <mukesh.rathor@xxxxxxxxxx> wrote:
> > > 
> > > > On Wed, 26 Sep 2012 12:33:39 +0100
> > 
> > 
> > > So for now, how about, lets go
> > > with what I've got. I'll make a note, and when I do xen patch, I'll
> > > figure it out, and would be a very small linux patch. I want to get
> > > linux patch in soon before the window closes.
> > 
> > We can leave page special as it is for now with very little
> > consequences, because it is not part of the interface with Xen.
> > However this is part of the interface, so whatever we choose here is
> > going to be hard to change later on.
> > 
> > I think it would be good if we could either make dom0 use a pfn or
> > domU use mfn, whatever is easier for you.
> 
> Ok, finally, focussing on this, the issue with pfn in dom0 is that
> I need pfn allocated in construct_dom0() and be mapped so that the
> guest can just do :
> 
> HYPERVISOR_shared_info=(struct shared_info 
> *)__va(xen_start_info->shared_info);
> 
> How about following I am experimenting with right now:
> 
> in construct_dom0():
> 
>     vstartinfo_end   = (vstartinfo_start +
>                         sizeof(struct start_info) +
>                         sizeof(struct dom0_vga_console_info));
> 
>     if ( is_hybrid_domain(d) ) {
>         start_info_pfn_addr = round_pgup(vstartinfo_end) - v_start;
>         vstartinfo_end   += PAGE_SIZE;
>     }
> 
> I can then put (PFN: start_info_pfn_addr)->(MFN: 
> virt_to_maddr(d->shared_info))
> in the p2m, and dom0 just has to do __va(), like domU does now.  I wont' need
> to special case dom0 then.
> 
> Do you foresee any problems with this approach?

Hard to say without all the surrounding context but it seems plausible
to me.

Ian.



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