linux-kernel - Re: [PATCH v7 1/3] KVM: x86: add support for user wait instructions

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Date:   Fri, 12 Jul 2019 08:13:00 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Tao Xu <tao3.xu@...el.com>
Cc:     pbonzini@...hat.com, rkrcmar@...hat.com, corbet@....net,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com,
        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 v7 1/3] KVM: x86: add support for user wait instructions

On Fri, Jul 12, 2019 at 04:29:05PM +0800, Tao Xu wrote:
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index 46af3a5e9209..a4d5da34b306 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -2048,6 +2048,7 @@ static void prepare_vmcs02_early(struct vcpu_vmx *vmx, struct vmcs12 *vmcs12)
>  				  SECONDARY_EXEC_ENABLE_INVPCID |
>  				  SECONDARY_EXEC_RDTSCP |
>  				  SECONDARY_EXEC_XSAVES |
> +				  SECONDARY_EXEC_ENABLE_USR_WAIT_PAUSE |
>  				  SECONDARY_EXEC_VIRTUAL_INTR_DELIVERY |
>  				  SECONDARY_EXEC_APIC_REGISTER_VIRT |
>  				  SECONDARY_EXEC_ENABLE_VMFUNC);
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index d98eac371c0a..f411c9ae5589 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -2247,6 +2247,7 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf,
>  			SECONDARY_EXEC_RDRAND_EXITING |
>  			SECONDARY_EXEC_ENABLE_PML |
>  			SECONDARY_EXEC_TSC_SCALING |
> +			SECONDARY_EXEC_ENABLE_USR_WAIT_PAUSE |
>  			SECONDARY_EXEC_PT_USE_GPA |
>  			SECONDARY_EXEC_PT_CONCEAL_VMX |
>  			SECONDARY_EXEC_ENABLE_VMFUNC |
> @@ -3984,6 +3985,25 @@ static void vmx_compute_secondary_exec_control(struct vcpu_vmx *vmx)
>  		}
>  	}
>  
> +	if (vmcs_config.cpu_based_2nd_exec_ctrl &
> +		SECONDARY_EXEC_ENABLE_USR_WAIT_PAUSE) {

This should be aligned with the beginning of the conditional.
Alternatively, add a vmx_waitpkg_supported() helper, which is fairly
ubiquitous even when there is only a single call site.

> +		/* Exposing WAITPKG only when WAITPKG is exposed */
No need for this comment.  It's also oddly worded, e.g. the second
"exposed" should probably be "enabled"?

> +		bool waitpkg_enabled =
> +			guest_cpuid_has(vcpu, X86_FEATURE_WAITPKG);
> +
> +		if (!waitpkg_enabled)
> +			exec_control &= ~SECONDARY_EXEC_ENABLE_USR_WAIT_PAUSE;
> +
> +		if (nested) {
> +			if (waitpkg_enabled)
> +				vmx->nested.msrs.secondary_ctls_high |=
> +					SECONDARY_EXEC_ENABLE_USR_WAIT_PAUSE;
> +			else
> +				vmx->nested.msrs.secondary_ctls_high &=
> +					~SECONDARY_EXEC_ENABLE_USR_WAIT_PAUSE;
> +		}
> +	}
> +
>  	vmx->secondary_exec_control = exec_control;
>  }
>  
> -- 
> 2.20.1
>