Re: [win-pv-devel] [PATCH 04/10] Separate checking upcall_pending in shared info from EvtchnPoll

[Matt Wilson <msw@xxxxxxxxx>]

On Wed, Dec 10, 2014 at 10:35:11AM -0800, Matt Wilson wrote:
> On Wed, Dec 10, 2014 at 05:38:04PM +0000, Paul Durrant wrote:
> > > -----Original Message-----
> > > From: Matt Wilson [mailto:mswilson@xxxxxxxxx] On Behalf Of Matt Wilson
> > > Sent: 10 December 2014 17:27
> > > To: Paul Durrant
> > > Cc: win-pv-devel@xxxxxxxxxxxxxxxxxxxx
> > > Subject: Re: [win-pv-devel] [PATCH 04/10] Separate checking upcall_pending
> > > in shared info from EvtchnPoll
> > > 
> > > On Wed, Dec 10, 2014 at 02:10:49PM +0000, Paul Durrant wrote:
> 
> [...]
> 
> > > >
> > > > That's a shame. The code really doesn't have much option but to use
> > > > this mechanism as Xen provides no explicit way for an HVM guest to
> > > > get vcpu ids until my patch "x86/hvm: Extend HVM cpuid leaf with
> > > > vcpu id" goes in and use of the FIFO ABI requires knowledge of vcpu
> > > > id.
> > > 
> > > Could you use the ACPI processor object ID number? Or use the initial
> > > APIC ID to ACPI processor ID mapping in the LAPIC part of MADT?
> > > 
> > 
> > Do you fix the ACPI tables up in EC2? I assume Windows uses ACPI to
> > number its CPUs so we could trust that value if we know it to match
> > the vcpu id.
> 
> Yes, the MADT LAPIC structs have the correct values. The
> acpi_processor_id field will be the index of the vCPU. The MADT LAPIC
> apic_id field will match the default APIC IDs returned by CPUID input
> EAX=1h output EBX[24..31], and input EAX=2b output EDX.
> 
> The legacy mptable is also indexed on vCPU ID, and contains the
> correct default APIC ID for each processor.

What do you think about using the Viridian MSR for Virtual Processor
Index as I mentioned on xen-devel?

  http://lists.xenproject.org/archives/html/xen-devel/2014-12/msg01352.html

--msw

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