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Subject: Re: [PATCH v6 2/3] KVM: vmx: Emulate MSR IA32_UMWAIT_CONTROL
To:     Tao Xu <tao3.xu@intel.com>, rkrcmar@redhat.com, corbet@lwn.net,
        tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, hpa@zytor.com,
        sean.j.christopherson@intel.com
Cc:     kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
        fenghua.yu@intel.com, xiaoyao.li@linux.intel.com,
        jingqi.liu@intel.com
References: <20190621055747.17060-1-tao3.xu@intel.com>
 <20190621055747.17060-3-tao3.xu@intel.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <43814a5e-12bf-ceb5-e4fb-12bbb32cd4cb@redhat.com>
Date:   Thu, 11 Jul 2019 15:25:12 +0200
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On 21/06/19 07:57, Tao Xu wrote:
> +	if (guest_cpuid_has(vcpu, X86_FEATURE_WAITPKG))
> +		atomic_switch_umwait_control_msr(vmx);
> +

guest_cpuid_has is slow.  Please replace it with a test on
secondary_exec_controls_get(vmx).

Are you going to look into nested virtualization support?  This should
include only 1) allowing setting the enable bit in secondary execution
controls, and passing it through in prepare_vmcs02_early; 2) reflecting
the vmexit in nested_vmx_exit_reflected.

Thanks,

Paolo