nVMX x86: Check VMX-preemption timer controls on vmentry of L2 guests

According to section "Checks on VMX Controls" in Intel SDM vol 3C, the
following check needs to be enforced on vmentry of L2 guests:

    If the "activate VMX-preemption timer" VM-execution control is 0, the
    the "save VMX-preemption timer value" VM-exit control must also be 0.
Signed-off-by: Krish Sadhukhan <krish.sadhukhan@oracle.com>
Reviewed-by: Mihai Carabas <mihai.carabas@oracle.com>
Reviewed-by: Liran Alon <liran.alon@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx.c

@@ -2084,6 +2084,12 @@ static inline bool nested_cpu_has_shadow_vmcs(struct vmcs12 *vmcs12)
 	return nested_cpu_has2(vmcs12, SECONDARY_EXEC_SHADOW_VMCS);
 }
 
+static inline bool nested_cpu_has_save_preemption_timer(struct vmcs12 *vmcs12)
+{
+	return vmcs12->vm_exit_controls &
+	    VM_EXIT_SAVE_VMX_PREEMPTION_TIMER;
+}
+
 static inline bool is_nmi(u32 intr_info)
 {
 	return (intr_info & (INTR_INFO_INTR_TYPE_MASK | INTR_INFO_VALID_MASK))
@@ -13051,6 +13057,10 @@ static int check_vmentry_prereqs(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12)
 	if (nested_vmx_check_msr_switch_controls(vcpu, vmcs12))
 		return VMXERR_ENTRY_INVALID_CONTROL_FIELD;
 
+	if (!nested_cpu_has_preemption_timer(vmcs12) &&
+	    nested_cpu_has_save_preemption_timer(vmcs12))
+		return VMXERR_ENTRY_INVALID_CONTROL_FIELD;
+
 	if (nested_vmx_check_pml_controls(vcpu, vmcs12))
 		return VMXERR_ENTRY_INVALID_CONTROL_FIELD;