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Re: [Xen-devel] [v5][PATCH 0/5] xen: add Intel IGD passthrough support

On Wed, Jun 25, 2014 at 11:54:22AM +0200, Paolo Bonzini wrote:
> Il 25/06/2014 11:50, Chen, Tiejun ha scritto:
> >>
> >>For past devices, we know which BARs they use.  For future devices, it
> >>would be nice if the PCH/MCH backdoor was specified so that we know they
> >>will leave a free BAR for virtualization.
> >>
> >
> >Now I'm a bit confused about BAR here.
> >
> >You're saying we will reserve a free BAR to address those information to
> >expose to guest, but which device does this free BAR belong to? The
> >video device? Or PCH/MCH?
> The video device.  If the host device does not have the BAR (which will be
> the common case), QEMU can emulate it like this:
> - offsets 0x0000..0x0fff map to configuration space of the host MCH
> - offsets 0x1000..0x1fff map to configuration space of the host PCH
> Of course this is only limited to offsets that are needed by the driver.
> Paolo

If you need hacks like this, describe this in ACPI.
But I really hope not.


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