Re: [PATCH v5 03/26] x86/hyperv: Update 'struct hv_enlightened_vmcs' definition

[Vitaly Kuznetsov]

Sean Christopherson <seanjc@xxxxxxxxxx> writes:

> On Mon, Aug 22, 2022, Vitaly Kuznetsov wrote:
>> So I reached out to Microsoft and their answer was that for all these new
>> eVMCS fields (including *PerfGlobalCtrl) observing architectural VMX
>> MSRs should be enough. *PerfGlobalCtrl case is special because of Win11
>> bug (if we expose the feature in VMX feature MSRs but don't set
>> CPUID.0x4000000A.EBX BIT(0) it just doesn't boot).
>
> Does this mean that KVM-on-HyperV needs to avoid using the PERF_GLOBAL_CTRL fields
> when the bit is not set?

It doesn't have to, based on the reply I got from Microsoft, if 
PERF_GLOBAL_CTRL is exposed in architectural VMX feature MSRs than eVMCS
fields are guaranteed to be present. The PV bit is 'extra'.

-- 
Vitaly