KVM: SVM: WARN if ir_list is non-empty at vCPU free

Now that AVIC IRTE tracking is in a mostly sane state, WARN if a vCPU is
freed with ir_list entries, i.e. if KVM leaves a dangling IRTE.

Initialize the per-vCPU interrupt remapping list and its lock even if AVIC
is disabled so that the WARN doesn't hit false positives (and so that KVM
doesn't need to call into AVIC code for a simple sanity check).

Link: https://lore.kernel.org/r/20250611224604.313496-54-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

arch/x86/kvm/svm/avic.c

@@ -705,6 +705,9 @@ int avic_init_vcpu(struct vcpu_svm *svm)
 	int ret;
 	struct kvm_vcpu *vcpu = &svm->vcpu;
 
+	INIT_LIST_HEAD(&svm->ir_list);
+	spin_lock_init(&svm->ir_list_lock);
+
 	if (!enable_apicv || !irqchip_in_kernel(vcpu->kvm))
 		return 0;
 
@@ -712,8 +715,6 @@ int avic_init_vcpu(struct vcpu_svm *svm)
 	if (ret)
 		return ret;
 
-	INIT_LIST_HEAD(&svm->ir_list);
-	spin_lock_init(&svm->ir_list_lock);
 	svm->dfr_reg = APIC_DFR_FLAT;
 
 	return ret;

arch/x86/kvm/svm/svm.c

@@ -1491,6 +1491,8 @@ static void svm_vcpu_free(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
 
+	WARN_ON_ONCE(!list_empty(&svm->ir_list));
+
 	svm_leave_nested(vcpu);
 	svm_free_nested(svm);