KVM: VMX: Drop explicit 'nested' check from vmx_set_cr4()

Drop vmx_set_cr4()'s explicit check on the 'nested' module param now
that common x86 handles the check by incorporating VMXE into the CR4
reserved bits, via kvm_cpu_caps.  X86_FEATURE_VMX is set in kvm_cpu_caps
(by vmx_set_cpu_caps()), if and only if 'nested' is true.

No functional change intended.
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20201007014417.29276-3-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/vmx.c

@@ -3123,18 +3123,13 @@ int vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
 		}
 	}
 
-	if (cr4 & X86_CR4_VMXE) {
 	/*
-		 * To use VMXON (and later other VMX instructions), a guest
-		 * must first be able to turn on cr4.VMXE (see handle_vmon()).
-		 * So basically the check on whether to allow nested VMX
-		 * is here.  We operate under the default treatment of SMM,
-		 * so VMX cannot be enabled under SMM.  Note, guest CPUID is
-		 * intentionally ignored, it's handled by cr4_guest_rsvd_bits.
-		 */
-		if (!nested || is_smm(vcpu))
+	 * We operate under the default treatment of SMM, so VMX cannot be
+	 * enabled under SMM.  Note, whether or not VMXE is allowed at all is
+	 * handled by kvm_valid_cr4().
+	 */
+	if ((cr4 & X86_CR4_VMXE) && is_smm(vcpu))
 		return 1;
-	}
 
 	if (vmx->nested.vmxon && !nested_cr4_valid(vcpu, cr4))
 		return 1;