RE: [PATCH v7 05/13] perf/x86/intel/pt: Introduce a new function to get capability of Intel PT

[Kang, Luwei]

> >> Can you elaborate on this, what information do we need besides
> >> MSR_IA32_VMX_MISC[14]?
> >
> > Enable Intel PT in guest depend on SECONDARY_EXEC_PT_USE_GPA, EPT,
> > MSR_IA32_VMX_MISC[14] and the capability of " PT_CAP_topa_output" on
> > hardware. PT driver will return " -ENODEV" if hardware not support
> > "PT_CAP_topa_output".
> 
> I actually don't understand why PT_CAP_topa_output matters for the purpose of enabling PT in the guest.  However you still need
> __pt_cap_get() in the CPUID checks.

Hi Paolo,
I think we should expose Intel Processor Trace to guest that can be detected and initialized. But without "PT_CAP_topa_output" Intel PT can't work in Linux.  So I add this feature as precondition. 
About why need this check in driver I think Alexander may know the reason.

Thanks,
Luwei Kang

> 
> Paolo