KVM: PPC: Book3S HV: Add missing HPTE unlock

In kvm_test_clear_dirty(), if we find an invalid HPTE we move on to the
next HPTE without unlocking the invalid one.  In fact we should never
find an invalid and unlocked HPTE in the rmap chain, but for robustness
we should unlock it.  This adds the missing unlock.
Reported-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Alexander Graf <agraf@suse.de>

arch/powerpc/kvm/book3s_64_mmu_hv.c

@@ -1117,8 +1117,11 @@ static int kvm_test_clear_dirty_npages(struct kvm *kvm, unsigned long *rmapp)
 		}
 
 		/* Now check and modify the HPTE */
-		if (!(hptep[0] & cpu_to_be64(HPTE_V_VALID)))
+		if (!(hptep[0] & cpu_to_be64(HPTE_V_VALID))) {
+			/* unlock and continue */
+			hptep[0] &= ~cpu_to_be64(HPTE_V_HVLOCK);
 			continue;
+		}
 
 		/* need to make it temporarily absent so C is stable */
 		hptep[0] |= cpu_to_be64(HPTE_V_ABSENT);