[PATCH 3.16.y-ckt 087/183] KVM: s390: floating irqs: fix user triggerable endless loop

[Luis Henriques]

3.16.7-ckt8 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: David Hildenbrand <dahi at linux.vnet.ibm.com>

commit 8e2207cdd087ebb031e9118d1fd0902c6533a5e5 upstream.

If a vm with no VCPUs is created, the injection of a floating irq
leads to an endless loop in the kernel.

Let's skip the search for a destination VCPU for a floating irq if no
VCPUs were created.

Reviewed-by: Dominik Dingel <dingel at linux.vnet.ibm.com>
Reviewed-by: Cornelia Huck <cornelia.huck at de.ibm.com>
Signed-off-by: David Hildenbrand <dahi at linux.vnet.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger at de.ibm.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 arch/s390/kvm/interrupt.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
index e2354f97264e..f19702fc89ec 100644
--- a/arch/s390/kvm/interrupt.c
+++ b/arch/s390/kvm/interrupt.c
@@ -925,6 +925,8 @@ static int __inject_vm(struct kvm *kvm, struct kvm_s390_interrupt_info *inti)
 		list_add_tail(&inti->list, &iter->list);
 	}
 	atomic_set(&fi->active, 1);
+	if (atomic_read(&kvm->online_vcpus) == 0)
+		goto unlock_fi;
 	sigcpu = find_first_bit(fi->idle_mask, KVM_MAX_VCPUS);
 	if (sigcpu == KVM_MAX_VCPUS) {
 		do {