1 files changed, 40 insertions, 1 deletions

diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 299351e77eb9..de4018a1bc4b 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -607,10 +607,45 @@ static int kvmppc_h_set_mode(struct kvm_vcpu *vcpu, unsigned long mflags,
 	}
 }
 
+static int kvm_arch_vcpu_yield_to(struct kvm_vcpu *target)
+{
+	struct kvmppc_vcore *vcore = target->arch.vcore;
+
+	/*
+	 * We expect to have been called by the real mode handler
+	 * (kvmppc_rm_h_confer()) which would have directly returned
+	 * H_SUCCESS if the source vcore wasn't idle (e.g. if it may
+	 * have useful work to do and should not confer) so we don't
+	 * recheck that here.
+	 */
+
+	spin_lock(&vcore->lock);
+	if (target->arch.state == KVMPPC_VCPU_RUNNABLE &&
+	    vcore->vcore_state != VCORE_INACTIVE)
+		target = vcore->runner;
+	spin_unlock(&vcore->lock);
+
+	return kvm_vcpu_yield_to(target);
+}
+
+static int kvmppc_get_yield_count(struct kvm_vcpu *vcpu)
+{
+	int yield_count = 0;
+	struct lppaca *lppaca;
+
+	spin_lock(&vcpu->arch.vpa_update_lock);
+	lppaca = (struct lppaca *)vcpu->arch.vpa.pinned_addr;
+	if (lppaca)
+		yield_count = lppaca->yield_count;
+	spin_unlock(&vcpu->arch.vpa_update_lock);
+	return yield_count;
+}
+
 int kvmppc_pseries_do_hcall(struct kvm_vcpu *vcpu)
 {
 	unsigned long req = kvmppc_get_gpr(vcpu, 3);
 	unsigned long target, ret = H_SUCCESS;
+	int yield_count;
 	struct kvm_vcpu *tvcpu;
 	int idx, rc;
 
@@ -646,7 +681,10 @@ int kvmppc_pseries_do_hcall(struct kvm_vcpu *vcpu)
 			ret = H_PARAMETER;
 			break;
 		}
-		kvm_vcpu_yield_to(tvcpu);
+		yield_count = kvmppc_get_gpr(vcpu, 5);
+		if (kvmppc_get_yield_count(tvcpu) != yield_count)
+			break;
+		kvm_arch_vcpu_yield_to(tvcpu);
 		break;
 	case H_REGISTER_VPA:
 		ret = do_h_register_vpa(vcpu, kvmppc_get_gpr(vcpu, 4),
@@ -1697,6 +1735,7 @@ static void kvmppc_run_core(struct kvmppc_vcore *vc)
 	vc->vcore_state = VCORE_STARTING;
 	vc->in_guest = 0;
 	vc->napping_threads = 0;
+	vc->conferring_threads = 0;
 
 	/*
 	 * Updating any of the vpas requires calling kvmppc_pin_guest_page,