Re: [Xen-devel] Xen PVH support in grub2

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Fri, Nov 03, 2017 at 07:23:50PM +0100, Juergen Gross wrote:
> On 03/11/17 19:19, Boris Ostrovsky wrote:
> > On 11/03/2017 02:05 PM, Juergen Gross wrote:
> >>
> >> So again the question: how to tell whether we are PVH or HVM in
> >> init_hypervisor_platform()? ACPi tables are scanned way later...
> > 
> > Can we make grub/OVMF append a boot option?
> > 
> > Or set setup_header.hardware_subarch to something? We already have
> > X86_SUBARCH_XEN but it is only used by PV.  Or we might be able to use
> > hardware_subarch_data (will need to get a buy-in from x86 maintainers, I
> > think).
> 
> But wouldn't this break the idea to reuse the native boot paths in
> grub/OVMF without further modifications?
> 
> I'd rather have a way to ask the hypervisor whether we are in PVH mode
> (e.g. via CPUID or a hypercall to test for a devicemodel having itself
> registered).

Keep in mind that from Xen's PoV PVH is just a HVM guest. Xen
currently keeps a bitmap of the emulated devices that are available to
a guest, but that's so far an internal field. We could consider
exporting this on a cpuid leaf, but then we need to make it a fixed
ABI.

Maybe we can make a list of platform devices that are not available on
PVH and that Linux assumes to be present?

Roger.

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