KVM: PPC: Book3S HV: Check wait conditions before sleeping in kvmppc_vcore_blocked

The kvmppc_vcore_blocked() code does not check for the wait condition
after putting the process on the wait queue. This means that it is
possible for an external interrupt to become pending, but the vcpu to
remain asleep until the next decrementer interrupt.  The fix is to
make one last check for pending exceptions and ceded state before
calling schedule().

Signed-off-by: Suresh Warrier <warrier@linux.vnet.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Alexander Graf <agraf@suse.de>

arch/powerpc/kvm/book3s_hv.c

@@ -1828,9 +1828,29 @@ static void kvmppc_wait_for_exec(struct kvm_vcpu *vcpu, int wait_state)
  */
 static void kvmppc_vcore_blocked(struct kvmppc_vcore *vc)
 {
+	struct kvm_vcpu *vcpu;
+	int do_sleep = 1;
+
 	DEFINE_WAIT(wait);
 
 	prepare_to_wait(&vc->wq, &wait, TASK_INTERRUPTIBLE);
+
+	/*
+	 * Check one last time for pending exceptions and ceded state after
+	 * we put ourselves on the wait queue
+	 */
+	list_for_each_entry(vcpu, &vc->runnable_threads, arch.run_list) {
+		if (vcpu->arch.pending_exceptions || !vcpu->arch.ceded) {
+			do_sleep = 0;
+			break;
+		}
+	}
+
+	if (!do_sleep) {
+		finish_wait(&vc->wq, &wait);
+		return;
+	}
+
 	vc->vcore_state = VCORE_SLEEPING;
 	spin_unlock(&vc->lock);
 	schedule();