KVM: x86: Skip KVM_GUESTDBG_BLOCKIRQ APICv update if APICv is disabled

Skip the APICv inhibit update for KVM_GUESTDBG_BLOCKIRQ if APICv is
disabled at the module level to avoid having to acquire the mutex and
potentially process all vCPUs. The DISABLE inhibit will (barring bugs)
never be lifted, so piling on more inhibits is unnecessary.

Fixes: cae72dcc ("KVM: x86: inhibit APICv when KVM_GUESTDBG_BLOCKIRQ active")
Cc: Maxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20220420013732.3308816-5-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/x86.c

@@ -10978,6 +10978,9 @@ static void kvm_arch_vcpu_guestdbg_update_apicv_inhibit(struct kvm *kvm)
 	struct kvm_vcpu *vcpu;
 	unsigned long i;
 
+	if (!enable_apicv)
+		return;
+
 	down_write(&kvm->arch.apicv_update_lock);
 
 	kvm_for_each_vcpu(i, vcpu, kvm) {