linux-kernel - Re: [PATCH v2 07/25] KVM: VMX: Set intercept for FRED MSRs

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Date: Wed, 12 Jun 2024 14:20:50 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Xin Li <xin3.li@...el.com>
Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org, 
	linux-doc@...r.kernel.org, linux-kselftest@...r.kernel.org, 
	pbonzini@...hat.com, corbet@....net, tglx@...utronix.de, mingo@...hat.com, 
	bp@...en8.de, dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com, 
	shuah@...nel.org, vkuznets@...hat.com, peterz@...radead.org, 
	ravi.v.shankar@...el.com, xin@...or.com
Subject: Re: [PATCH v2 07/25] KVM: VMX: Set intercept for FRED MSRs

On Wed, Feb 07, 2024, Xin Li wrote:
> @@ -7774,10 +7777,12 @@ static void update_intel_pt_cfg(struct kvm_vcpu *vcpu)
>  static void vmx_vcpu_config_fred_after_set_cpuid(struct kvm_vcpu *vcpu)
>  {
>  	struct vcpu_vmx *vmx = to_vmx(vcpu);
> +	bool fred_enumerated;
>  
>  	kvm_governed_feature_check_and_set(vcpu, X86_FEATURE_FRED);
> +	fred_enumerated = guest_can_use(vcpu, X86_FEATURE_FRED);

"enumerated" isn't correct.  Userspace can enumerate FRED to the guest even if
FRED is unsupported in KVM.

Planning for a future where this becomes guest_cpu_cap_has(), maybe "has_fred"?

> -	if (guest_can_use(vcpu, X86_FEATURE_FRED)) {
> +	if (fred_enumerated) {
>  		vm_entry_controls_setbit(vmx, VM_ENTRY_LOAD_IA32_FRED);
>  		secondary_vm_exit_controls_setbit(vmx,
>  						  SECONDARY_VM_EXIT_SAVE_IA32_FRED |
> @@ -7788,6 +7793,16 @@ static void vmx_vcpu_config_fred_after_set_cpuid(struct kvm_vcpu *vcpu)
>  						    SECONDARY_VM_EXIT_SAVE_IA32_FRED |
>  						    SECONDARY_VM_EXIT_LOAD_IA32_FRED);
>  	}
> +
> +	vmx_set_intercept_for_msr(vcpu, MSR_IA32_FRED_RSP0, MSR_TYPE_RW, !fred_enumerated);
> +	vmx_set_intercept_for_msr(vcpu, MSR_IA32_FRED_RSP1, MSR_TYPE_RW, !fred_enumerated);
> +	vmx_set_intercept_for_msr(vcpu, MSR_IA32_FRED_RSP2, MSR_TYPE_RW, !fred_enumerated);
> +	vmx_set_intercept_for_msr(vcpu, MSR_IA32_FRED_RSP3, MSR_TYPE_RW, !fred_enumerated);
> +	vmx_set_intercept_for_msr(vcpu, MSR_IA32_FRED_STKLVLS, MSR_TYPE_RW, !fred_enumerated);
> +	vmx_set_intercept_for_msr(vcpu, MSR_IA32_FRED_SSP1, MSR_TYPE_RW, !fred_enumerated);
> +	vmx_set_intercept_for_msr(vcpu, MSR_IA32_FRED_SSP2, MSR_TYPE_RW, !fred_enumerated);
> +	vmx_set_intercept_for_msr(vcpu, MSR_IA32_FRED_SSP3, MSR_TYPE_RW, !fred_enumerated);
> +	vmx_set_intercept_for_msr(vcpu, MSR_IA32_FRED_CONFIG, MSR_TYPE_RW, !fred_enumerated);
>  }
>  
>  static void vmx_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
> -- 
> 2.43.0
>