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Date:   Mon, 5 Sep 2022 17:06:47 +0000
From:   Wei Liu <wei.liu@kernel.org>
To:     Vitaly Kuznetsov <vkuznets@redhat.com>
Cc:     kvm@vger.kernel.org, Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <seanjc@google.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Michael Kelley <mikelley@microsoft.com>,
        Yuan Yao <yuan.yao@linux.intel.com>,
        Maxim Levitsky <mlevitsk@redhat.com>,
        linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org,
        Wei Liu <wei.liu@kernel.org>
Subject: Re: [PATCH v6 02/33] x86/hyperv: Update 'struct hv_enlightened_vmcs'
 definition
Message-ID: <20220905170647.ky7rf5ypmqwxb7wx@liuwe-devbox-debian-v2>
References: <20220830133737.1539624-1-vkuznets@redhat.com>
 <20220830133737.1539624-3-vkuznets@redhat.com>
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On Tue, Aug 30, 2022 at 03:37:06PM +0200, Vitaly Kuznetsov wrote:
> Updated Hyper-V Enlightened VMCS specification lists several new
> fields for the following features:
> 
> - PerfGlobalCtrl
> - EnclsExitingBitmap
> - Tsc Scaling
> - GuestLbrCtl
> - CET
> - SSP
> 
> Update the definition.
> 
> Note, the updated spec also provides an additional CPUID feature flag,
> CPUIDD.0x4000000A.EBX BIT(0), for PerfGlobalCtrl to workaround a Windows
> 11 quirk.  Despite what the TLFS says:
> 
>   Indicates support for the GuestPerfGlobalCtrl and HostPerfGlobalCtrl
>   fields in the enlightened VMCS.
> 
> guests can safely use the fields if they are enumerated in the
> architectural VMX MSRs.  I.e. KVM-on-HyperV doesn't need to check the
> CPUID bit, but KVM-as-HyperV must ensure the bit is set if PerfGlobalCtrl
> fields are exposed to L1.
> 
> https://docs.microsoft.com/en-us/virtualization/hyper-v-on-windows/tlfs/tlfs
> 
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> [sean: tweak CPUID name to make it PerfGlobalCtrl only]
> Signed-off-by: Sean Christopherson <seanjc@google.com>

Acked-by: Wei Liu <wei.liu@kernel.org>