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SubjectRe: [PATCH RESEND 1/1] X86: Handle Hyper-V vmbus interrupts as special hypervisor interrupts
On Fri, Jan 25, Jan Beulich wrote:

> >>> On 24.01.13 at 19:59, Olaf Hering <olaf@aepfle.de> wrote:
> > On Thu, Jan 24, KY Srinivasan wrote:
> >
> >
> >> > Question is - considering you stated that this is supported
> >> > starting in Win8, doesn't Hyper-V itself announce that
> >> > capability in some explicit way?
> >>
> >> Thanks Jan. Unfortunately I don't think tis interrupt delivery model
> >> is specified via a "feature" bit (I will check with the Windows guys).
> >> Perhaps, we can have a Hyper-V specific compilation switch to address
> >> the Xen emulation issue.
> >
> > Would that really help if both pvops XEN_PVHVM and HYPERV are enabled in
> > the config? I assume at this point the access to the DMI data is not yet
> > possible.
>
> As just said in another reply - with XEN_PVHVM, there's no problem,
> since Xen gets checked for first. There's only a problem when
> !XEN_PVHVM, because in that case Hyper-V will be probed for.
> And the problem can only get bigger when on top of that the
> out-of-tree PV drivers are intended to be used.

Yes, xen_cpuid_base() recognizes Xen as hypervisor even with
'viridian=1' in the .cfg file.
I think if there is no feature bit for this, the DMI can be used
because its appearently available before the host is checked:

...
[ 0.000000] NX (Execute Disable) protection: active
[ 0.000000] DMI 2.4 present.
[ 0.000000] DMI: Xen HVM domU, BIOS 4.1.3_06-0.7.1 12/05/2012
[ 0.000000] Hypervisor detected: Microsoft HyperV
[ 0.000000] HyperV: features 0x70, hints 0x0
[ 0.000000] e820 update range: 0000000000000000 - 0000000000010000 (usable) ==> (reserved)
...

Olaf


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