From: Kamble, Nitin A
Sent: Tuesday, September 30, 2008
10:45 AM
To: 'Keir Fraser'
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: RE: [Xen-devel] Re: cpuid
information to hvm guest
Thanks & Regards,
Nitin
Linux Open Source
Technology Center, Intel Corporation
--------------------------------------------------------------------------------
The Mind is like a
parachute; it works much better when it's open.
From: Keir Fraser
[mailto:keir.fraser@xxxxxxxxxxxxx]
Sent: Tuesday, September 30, 2008
2:15 AM
To: Kamble, Nitin A
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-devel] Re: cpuid
information to hvm guest
I applied a patch that does this as
changeset 18560.
-- Keir
On 29/9/08 22:30, "Keir Fraser" <keir.fraser@xxxxxxxxxxxxx>
wrote:
How about the following changes to
our default HVM CPUID?
Guest_CPUID.1:EBX[23:17] = Host_CPUID.1:EBX[22:16]
Guest_CPUID.1:EBX[16] = 0
Guest_CPUID.4:EAX[31:27] = Host_CPUID.4:EAX[30:26]
Guest_CPUID.4:EAX[26] = 1
Guest_CPUID.1:EDX[28] = Host_CPUID.1:EDX[28]
Basically pass-through HT/multicore support, but specify max-cores-per-package
and max-threads-per-package as twice the host values. This deals with the fact
our virtual APIC IDs are 2*VCPUID.
-- Keir
On 29/9/08 21:15, "Keir Fraser" <keir.fraser@xxxxxxxxxxxxx>
wrote:
I’d be happy, by default, for
xend to detect threads-per-socket on the host system and replicate that on
guest CPUID. I don’t see how direct pass-through of host CPUID values can
work, because for example host LAPIC identifiers may be guest different from
guest vLAPIC identifiers. So I won’t apply anything like your original
patches, period.
-- Keir
On 29/9/08 18:48, "Kamble, Nitin A" <nitin.a.kamble@xxxxxxxxx>
wrote:
Hiding those details by default is a good strategy
we’d like to maintain.
[Nitin>]
Why do you say it is a good strategy? What are the benefits associated with it?
Furthermore we cannot change CPU-to-LAPIC identifier
mapping without breaking saved guest images, which is not acceptable.
[Nitin>]
I am not clear on this part, how saved guest images get broken? I think
this change is like upgrading BIOS. It should not break guest images.
If our hiding of host information is broken, we’d
like a patch to fix it; likewise any other CPUID inconsistency. What specific
issues are you seeing?
[Nitin>]
This is an issue with OS which have licensing restriction on CPUs. A customer
reported to us that they were not seeing all cpus on windows server because Xen
is exposing each vcpu as a socket on a multi-core host system.
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