Re: [PATCH 0/9] Intel Processor Trace virtulization enabling

[Paolo Bonzini]

On 23/10/2017 10:01, Kang, Luwei wrote:
> 
>>> So, can we enable it in L1
>>> guest only first?  I think it is not worth to disable EPT for L1 to
>>> enable intel PT. what is your opinion?
>> Yes, we can enable it.  But since KVM sets IA32_VMX_MISC[14]=0, your patches must forbid enabling processor trace during VMX
>> operation.
>
> L1 hypervisor can't  get the capability of " TraceEn can be set in
> VMX operation (IA32_VMX_MISC[bit 14] is 0)" and set it to 0. We need
> to trap whether L1 hypervisor have enable VMXON, and forbid enable PT
> when vmxon. Is that right? Or have something else?

Correct.  I don't have the SDM at hand, so I'm not sure what happens if
you do a VMXON while TraceEn is 1.  However, that has to be handled as well.

Paolo