KVM: x86/xen: Initialize hrtimer in kvm_xen_init_vcpu()

The hrtimer is initialized in the KVM_XEN_VCPU_SET_ATTR ioctl. That caused
problem in the past, because the hrtimer can be initialized multiple times,
which was fixed by commit af735db ("KVM: x86/xen: Initialize Xen timer
only once"). This commit avoids initializing the timer multiple times by
checking the field 'function' of struct hrtimer to determine if it has
already been initialized.

This is not required and in the way to make the function field private.

Move the hrtimer initialization into kvm_xen_init_vcpu() so that it will
only be initialized once.

Signed-off-by: Nam Cao <namcao@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/all/9c33c7224d97d08f4fa30d3cc8687981c1d3e953.1730386209.git.namcao@linutronix.de

Author: covanam

arch/x86/kvm/xen.c

@@ -263,13 +263,6 @@ static void kvm_xen_stop_timer(struct kvm_vcpu *vcpu)
 	atomic_set(&vcpu->arch.xen.timer_pending, 0);
 }
 
-static void kvm_xen_init_timer(struct kvm_vcpu *vcpu)
-{
-	hrtimer_init(&vcpu->arch.xen.timer, CLOCK_MONOTONIC,
-		     HRTIMER_MODE_ABS_HARD);
-	vcpu->arch.xen.timer.function = xen_timer_callback;
-}
-
 static void kvm_xen_update_runstate_guest(struct kvm_vcpu *v, bool atomic)
 {
 	struct kvm_vcpu_xen *vx = &v->arch.xen;
@@ -1070,9 +1063,6 @@ int kvm_xen_vcpu_set_attr(struct kvm_vcpu *vcpu, struct kvm_xen_vcpu_attr *data)
 			break;
 		}
 
-		if (!vcpu->arch.xen.timer.function)
-			kvm_xen_init_timer(vcpu);
-
 		/* Stop the timer (if it's running) before changing the vector */
 		kvm_xen_stop_timer(vcpu);
 		vcpu->arch.xen.timer_virq = data->u.timer.port;
@@ -2235,6 +2225,8 @@ void kvm_xen_init_vcpu(struct kvm_vcpu *vcpu)
 	vcpu->arch.xen.poll_evtchn = 0;
 
 	timer_setup(&vcpu->arch.xen.poll_timer, cancel_evtchn_poll, 0);
+	hrtimer_init(&vcpu->arch.xen.timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_HARD);
+	vcpu->arch.xen.timer.function = xen_timer_callback;
 
 	kvm_gpc_init(&vcpu->arch.xen.runstate_cache, vcpu->kvm);
 	kvm_gpc_init(&vcpu->arch.xen.runstate2_cache, vcpu->kvm);