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Re: [Xen-devel] [PATCH v8 13/14] tools/libxl: explicitly grant access to needed I/O-memory ranges

On Mon, 2014-05-26 at 12:15 +0100, Jan Beulich wrote:
> >>> IHMO, the guest doesn't need to have permission to this region. When
> >>> QEMU ask to map this region to the guest, the hypercall will only check
> >>> the permission on the domain where QEMU is running. Therefore, the
> >>> permission should be given to the stubdomain.
> >>
> >> How would qemu be involved in I/O from/to a passed through
> >> device?
> > 
> > AFAIU, the mapping of the range 0xa0000-* will be done by QEMU for an 
> > HVM guest (i.e calling xc_domain_memory_mapping).
> If qemu is mapping this _machine_ range to every guest (or every
> guest getting a GFX device passed through) that would be wrong
> then too afaict.

How does this work today then? Do no guests get access to 0xa0000 or do
we some how determine which of the multiple GFX devices is the primary
one (with the real 0xa0000 mapped to it)?

I can't see 0xa0000 mapped by anything in xen.git and there are too many
hits on the qemu tree for me to spot it if it is there.


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