linux-kernel - Re: [PATCH 1/4] KVM: x86: Disable intercept for CORE cstate read

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Message-ID: <7787e0cb-2c46-b5b5-94ea-72c061ea0235@redhat.com>
Date:   Mon, 20 May 2019 12:30:40 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     Radim Krčmář <rkrcmar@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Liran Alon <liran.alon@...cle.com>
Subject: Re: [PATCH 1/4] KVM: x86: Disable intercept for CORE cstate read

On 17/05/19 10:49, Wanpeng Li wrote:
> From: Wanpeng Li <wanpengli@...cent.com>
> 
> Allow guest reads CORE cstate when exposing host CPU power management capabilities 
> to the guest. PKG cstate is restricted to avoid a guest to get the whole package 
> information in multi-tenant scenario.

Hmm, I am not sure about this.  I can see why it can be useful to run
turbostat in the guest, but is it a good idea to share it with the
guest, since it counts from machine reset rather than from VM reset?

Maybe it could use a separate bit for KVM_CAP_X86_DISABLE_EXITS?

Thanks,

Paolo

> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Radim Krčmář <rkrcmar@...hat.com>
> Cc: Sean Christopherson <sean.j.christopherson@...el.com>
> Cc: Liran Alon <liran.alon@...cle.com>
> Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
> ---
>  arch/x86/kvm/vmx/vmx.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 771d3bf..b0d6be5 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -6615,6 +6615,12 @@ static struct kvm_vcpu *vmx_create_vcpu(struct kvm *kvm, unsigned int id)
>  	vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_SYSENTER_CS, MSR_TYPE_RW);
>  	vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_SYSENTER_ESP, MSR_TYPE_RW);
>  	vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_SYSENTER_EIP, MSR_TYPE_RW);
> +	if (kvm_mwait_in_guest(kvm)) {
> +		vmx_disable_intercept_for_msr(msr_bitmap, MSR_CORE_C1_RES, MSR_TYPE_R);
> +		vmx_disable_intercept_for_msr(msr_bitmap, MSR_CORE_C3_RESIDENCY, MSR_TYPE_R);
> +		vmx_disable_intercept_for_msr(msr_bitmap, MSR_CORE_C6_RESIDENCY, MSR_TYPE_R);
> +		vmx_disable_intercept_for_msr(msr_bitmap, MSR_CORE_C7_RESIDENCY, MSR_TYPE_R);
> +	}
>  	vmx->msr_bitmap_mode = 0;
>  
>  	vmx->loaded_vmcs = &vmx->vmcs01;
>