s390x/async_pf: Check for apf extension and enable pfault

S390 can also use async page faults, to enhance guest scheduling.
In case of live migration we want to disable the feature and let
all pending request finish.

Signed-off-by: Dominik Dingel <dingel@linux.vnet.ibm.com>
Signed-off-by: Jens Freimann <jfrei@linux.vnet.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
diff --git a/target-s390x/cpu.c b/target-s390x/cpu.c
index ff57b80..f1319e5 100644
--- a/target-s390x/cpu.c
+++ b/target-s390x/cpu.c
@@ -83,6 +83,7 @@
     S390CPUClass *scc = S390_CPU_GET_CLASS(cpu);
     CPUS390XState *env = &cpu->env;
 
+    env->pfault_token = -1UL;
     s390_del_running_cpu(cpu);
     scc->parent_reset(s);
 #if !defined(CONFIG_USER_ONLY)
@@ -105,6 +106,8 @@
     /* architectured initial values for CR 0 and 14 */
     env->cregs[0] = CR0_RESET;
     env->cregs[14] = CR14_RESET;
+
+    env->pfault_token = -1UL;
 }
 
 /* CPUClass:reset() */
@@ -123,6 +126,9 @@
     /* architectured initial values for CR 0 and 14 */
     env->cregs[0] = CR0_RESET;
     env->cregs[14] = CR14_RESET;
+
+    env->pfault_token = -1UL;
+
     /* set halted to 1 to make sure we can add the cpu in
      * s390_ipl_cpu code, where CPUState::halted is set back to 0
      * after incrementing the cpu counter */