linux-kernel - Re: [PATCH v6 2/3] KVM: vmx: Emulate MSR IA32_UMWAIT

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Date:   Thu, 11 Jul 2019 15:25:12 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Tao Xu <tao3.xu@...el.com>, rkrcmar@...hat.com, corbet@....net,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com,
        sean.j.christopherson@...el.com
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        fenghua.yu@...el.com, xiaoyao.li@...ux.intel.com,
        jingqi.liu@...el.com
Subject: Re: [PATCH v6 2/3] KVM: vmx: Emulate MSR IA32_UMWAIT_CONTROL

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