Re: QEMU PIC indirection patch for in-kernel APIC work

Nakajima, Jun
2007-04-04T15:36:04Z

Avi Kivity wrote:
> Anthony Liguori wrote:
>> Avi Kivity wrote:
>>> Anthony Liguori wrote:
>>>>
>>>> Then again, are we really positive that we have to move the APIC
>>>> into the kernel? A lot of things will get much more complicated.
>>>
>>> The following arguments are in favor:
>>> - allow in-kernel paravirt drivers to interrupt the guest without
>>> going through qemu (which involves a signal and some complexity)
>>> - same for guest SMP IPI
>>> - reduced overhead for a much-loved hardware component (especially
>>> on Windows, where one regularly sees 100K apic updates a second)
>>
>> This is for the TPR right? VT has special logic to handle TPR
>> virtualization doesn't it? I thought SVM did too...
>>
>
> Yes, the TPR. Both VT and SVM virtualize CR8 in 64-bit mode. SVM
> also supports CR8 in 32-bit mode through a nwe instruction encoding,
> but
> nobody uses that to my knowledge. Maybe some brave soul can hack kvm
> to patch the new instruction in place of the mmio instruction Windows
> uses
> to bang on the tpr.

Actually VT has virtual TPR support that does not require CR8. We
submitted a patch for Xen. Please see
http://lists.xensource.com/archives/html/xen-devel/2007-03/msg00993.html
The spec should be available soon. We are working on a patch for KVM.

Jun
---
Intel Open Source Technology Center