linux-kernel - Re: [PATCH v5 03/26] x86/hyperv: Update 'struct hv_enlightened

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Message-ID: <87bkscxn3r.fsf@redhat.com>
Date:   Mon, 22 Aug 2022 18:24:40 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Anirudh Rayabharam <anrayabh@...ux.microsoft.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Michael Kelley <mikelley@...rosoft.com>,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 03/26] x86/hyperv: Update 'struct
 hv_enlightened_vmcs' definition

Sean Christopherson <seanjc@...gle.com> 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