> -Original Message-
> From: Matt Wilson [mailto:mswil...@gmail.com] On Behalf Of Matt Wilson
> Sent: 11 December 2014 23:17
> To: Paul Durrant
> Cc: xen-devel@lists.xen.org; Keir (Xen.org); Jan Beulich
> Subject: Re: [Xen-devel] [PATCH v2] x86/hvm: Extend HVM cpuid leaf with
> vcpu id
>
> On Thu, Nov 06, 2014 at 03:26:24PM +, Paul Durrant wrote:
> > To perform certain hypercalls HVM guests need to use Xen's idea of
> > vcpu id, which may well not match the guest OS idea of CPU id.
> > This patch adds vcpu id to the HVM cpuid leaf allowing the guest
> > to build a mapping.
>
> One more tangent on this, since this is partially considered in a
> Windows context. Why not use the existing Viridian virtual processor
> index MSR for this, since that would work on Xen today.
>
> xen/arch/x86/hvm/viridian.c:
> > #define VIRIDIAN_MSR_VP_INDEX 0x4002
> > ...
> > case VIRIDIAN_MSR_VP_INDEX:
> >perfc_incr(mshv_rdmsr_vp_index);
> >*val = v->vcpu_id;
> >break;
>
Yes, that would work for VMs where viridian is enabled, but there's no
requirement that viridian is enabled to install PV drivers even in Windows. I
guess ACPI is the only robust way to get vcpu id in an HVM guest in the absence
of the new cpuid leaf.
Paul
> --msw
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