KVM: nVMX: do not start the preemption timer hrtimer unnecessarily

The preemption timer can be started even if there is a vmentry
failure during or after loading guest state.  That is pointless,
move the call after all conditions have been checked.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/nested.c

@@ -2278,10 +2278,6 @@ static int prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12,
 	}
 	vmx_set_rflags(vcpu, vmcs12->guest_rflags);
 
-	vmx->nested.preemption_timer_expired = false;
-	if (nested_cpu_has_preemption_timer(vmcs12))
-		vmx_start_preemption_timer(vcpu);
-
 	/* EXCEPTION_BITMAP and CR0_GUEST_HOST_MASK should basically be the
 	 * bitwise-or of what L1 wants to trap for L2, and what we want to
 	 * trap. Note that CR0.TS also needs updating - we do this later.
@@ -3018,6 +3014,15 @@ int nested_vmx_enter_non_root_mode(struct kvm_vcpu *vcpu, bool from_vmentry)
 	if (unlikely(evaluate_pending_interrupts))
 		kvm_make_request(KVM_REQ_EVENT, vcpu);
 
+	/*
+	 * Do not start the preemption timer hrtimer until after we know
+	 * we are successful, so that only nested_vmx_vmexit needs to cancel
+	 * the timer.
+	 */
+	vmx->nested.preemption_timer_expired = false;
+	if (nested_cpu_has_preemption_timer(vmcs12))
+		vmx_start_preemption_timer(vcpu);
+
 	/*
 	 * Note no nested_vmx_succeed or nested_vmx_fail here. At this point
 	 * we are no longer running L1, and VMLAUNCH/VMRESUME has not yet