linux-kernel - Re: [PATCH v4 16/19] KVM: nVMX: Add support for the secondary VM exit controls

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Message-ID: <aFrYM2urBeoFDVAV@google.com>
Date: Tue, 24 Jun 2025 09:54:11 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: "Xin Li (Intel)" <xin@...or.com>
Cc: pbonzini@...hat.com, kvm@...r.kernel.org, linux-doc@...r.kernel.org, 
	linux-kernel@...r.kernel.org, corbet@....net, tglx@...utronix.de, 
	mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com, x86@...nel.org, 
	hpa@...or.com, andrew.cooper3@...rix.com, luto@...nel.org, 
	peterz@...radead.org, chao.gao@...el.com, xin3.li@...el.com
Subject: Re: [PATCH v4 16/19] KVM: nVMX: Add support for the secondary VM exit controls

On Fri, Mar 28, 2025, Xin Li (Intel) wrote:
> diff --git a/arch/x86/kvm/vmx/capabilities.h b/arch/x86/kvm/vmx/capabilities.h
> index b4f49a4690ca..d29be4e4124e 100644
> --- a/arch/x86/kvm/vmx/capabilities.h
> +++ b/arch/x86/kvm/vmx/capabilities.h
> @@ -38,6 +38,7 @@ struct nested_vmx_msrs {
>  	u32 pinbased_ctls_high;
>  	u32 exit_ctls_low;
>  	u32 exit_ctls_high;
> +	u64 secondary_exit_ctls;
>  	u32 entry_ctls_low;
>  	u32 entry_ctls_high;
>  	u32 misc_low;
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index 5504d9e9fd32..8b0c5e5f1e98 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -1457,6 +1457,7 @@ int vmx_set_vmx_msr(struct kvm_vcpu *vcpu, u32 msr_index, u64 data)
>  	case MSR_IA32_VMX_PINBASED_CTLS:
>  	case MSR_IA32_VMX_PROCBASED_CTLS:
>  	case MSR_IA32_VMX_EXIT_CTLS:
> +	case MSR_IA32_VMX_EXIT_CTLS2:

This is wrong.  KVM allows userspace to configure control MSRs, it's just the
non-true MSRs that have a true version that KVM rejects.  I.e. KVM needs to
actually handle writing MSR_IA32_VMX_EXIT_CTLS2.

>  	case MSR_IA32_VMX_ENTRY_CTLS:
>  		/*
>  		 * The "non-true" VMX capability MSRs are generated from the