Re: [PATCH v4 5/8] KVM: nVMX: Add a quirk for KVM tweaks to VMX control MSRs

[Sean Christopherson <seanjc@google.com>]

On Tue, Mar 01, 2022, Oliver Upton wrote:
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 224ef4c19a5d..21b98bad1319 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -7250,6 +7250,9 @@ void nested_vmx_entry_exit_ctls_update(struct kvm_vcpu *vcpu)
>  {
>  	struct vcpu_vmx *vmx = to_vmx(vcpu);
>  
> +	if (!kvm_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_TWEAK_VMX_CTRL_MSRS))
> +		return;
> +
>  	if (kvm_mpx_supported()) {
>  		bool mpx_enabled = guest_cpuid_has(vcpu, X86_FEATURE_MPX);

Assuming the proposed L2 CR4 checking changes don't throw a wrench in things, I'd
I'd prefer we include the CR4 fixed1 massaging in the quirk:

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index ce0000202c5e..17b19946d6cc 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7367,7 +7367,8 @@ static void vmx_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
                        ~(FEAT_CTL_VMX_ENABLED_INSIDE_SMX |
                          FEAT_CTL_VMX_ENABLED_OUTSIDE_SMX);

-       if (nested_vmx_allowed(vcpu)) {
+       if (nested_vmx_allowed(vcpu) &&
+           !kvm_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_TWEAK_VMX_CTRL_MSRS)) {
                nested_vmx_cr_fixed1_bits_update(vcpu);
                nested_vmx_entry_exit_ctls_update(vcpu);
        }