Re: [Xen-devel] [PATCH v14 02/17] libxc: Move temporary grant table mapping to end of memory

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2013-11-05 at 11:57 +0100, Roger Pau Monnà wrote:
> Ccing tools maintainers.
> 
> On 04/11/13 13:14, George Dunlap wrote:
> > From: Roger Pau Monnà <roger.pau@xxxxxxxxxx>
> > 
> > In order to set up the grant table for HVM guests, libxc needs to map
> > the grant table temporarily.  At the moment, it does this by adding the
> > grant page to the HVM guest's p2m table in the MMIO hole (at gfn 0xFFFFE),
> > then mapping that gfn, setting up the table, then unmapping the gfn and
> > removing it from the p2m table.
> > 
> > This breaks with PVH guests with 4G or more of ram, because there is
> > no MMIO hole; so it ends up clobbering a valid RAM p2m entry, then
> > leaving a "hole" when it removes the grant map from the p2m table.
> > Since the guest thinks this is normal ram, when it maps it and tries
> > to access the page, it crashes.
> > 
> > This patch maps the page at max_gfn+1 instead.
> > 
> > Signed-off-by: Roger Pau Monnà <roger.pau@xxxxxxxxxx>

Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>



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