Merge tag 'kvm-s390-master-20150730' of git://git.kernel.org/pub/scm/…

…linux/kernel/git/kvms390/linux into kvm-master

KVM: s390: bugfix for kvm/master (4.2)

Here is a bugfix for a regression that was introduced after 4.1
with the commit commit 785dbef ("KVM: s390: optimize round
trip time in request handling"). After lots of cpu hotplugs in the
guest (online/offline) sometimes a guest CPU did loop within host
KVM code. Reason was that PROG_REQUEST was set in the sie control
block, but no request was pending. This made commit 785dbef
the suspect and changing that area to always reset PROG_REQUEST
did indeed fix the problem.

Special thanks to David Hildenbrand, who helped understanding the
exact sequence that led to the problem.

arch/s390/kvm/kvm-s390.c

@@ -1742,10 +1742,10 @@ static bool ibs_enabled(struct kvm_vcpu *vcpu)
 
 static int kvm_s390_handle_requests(struct kvm_vcpu *vcpu)
 {
-	if (!vcpu->requests)
-		return 0;
 retry:
 	kvm_s390_vcpu_request_handled(vcpu);
+	if (!vcpu->requests)
+		return 0;
 	/*
 	 * We use MMU_RELOAD just to re-arm the ipte notifier for the
 	 * guest prefix page. gmap_ipte_notify will wait on the ptl lock.