KVM: Don't accept obviously wrong gsi values via KVM_IRQFD

We cannot add routes for gsi values >= KVM_MAX_IRQ_ROUTES -- see
kvm_set_irq_routing(). Hence, there is no sense in accepting them
via KVM_IRQFD. Prevent them from entering the system in the first
place.

Signed-off-by: Jan H. Schönherr <jschoenh@amazon.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
static int kvm_deassign_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args)
{
	enum kvm_bus bus_idx = ioeventfd_bus_from_flags(args->flags);
	int ret = kvm_deassign_ioeventfd_idx(kvm, bus_idx, args);

	if (!args->len && bus_idx == KVM_MMIO_BUS)
		kvm_deassign_ioeventfd_idx(kvm, KVM_FAST_MMIO_BUS, args);

	return ret;
}

static int kvm_deassign_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args)
{
	enum kvm_bus bus_idx = ioeventfd_bus_from_flags(args->flags);
	int ret = kvm_deassign_ioeventfd_idx(kvm, bus_idx, args);

	if (!args->len && bus_idx == KVM_MMIO_BUS)
		kvm_deassign_ioeventfd_idx(kvm, KVM_FAST_MMIO_BUS, args);

	return ret;
}
