Add support for async page fault to qemu

index 85ed30f..166c2a4 100644
@@ -680,6 +680,7 @@ typedef struct CPUX86State {
 #endif
     uint64_t system_time_msr;
     uint64_t wall_clock_msr;
+    uint64_t async_pf_en_msr;
 
     uint64_t tsc;
 

index 0e0bf60..49f1067 100644
@@ -73,7 +73,7 @@ static const char *ext3_feature_name[] = {
 };
 
 static const char *kvm_feature_name[] = {
-    "kvmclock", "kvm_nopiodelay", "kvm_mmu", NULL, NULL, NULL, NULL, NULL,
+    "kvmclock", "kvm_nopiodelay", "kvm_mmu", NULL, "kvm_asyncpf", NULL, NULL, NULL,
     NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL,
     NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL,
     NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL,

index ae0a034..7dfc357 100644
@@ -162,6 +162,9 @@ struct kvm_para_features {
 #ifdef KVM_CAP_PV_MMU
         { KVM_CAP_PV_MMU, KVM_FEATURE_MMU_OP },
 #endif
+#ifdef KVM_CAP_ASYNC_PF
+        { KVM_CAP_ASYNC_PF, KVM_FEATURE_ASYNC_PF },
+#endif
         { -1, -1 }
 };
 

@@ -838,6 +841,9 @@ static int kvm_put_msrs(CPUState *env, int level)
         kvm_msr_entry_set(&msrs[n++], MSR_KVM_SYSTEM_TIME,
                           env->system_time_msr);
         kvm_msr_entry_set(&msrs[n++], MSR_KVM_WALL_CLOCK, env->wall_clock_msr);
+#ifdef KVM_CAP_ASYNC_PF
+        kvm_msr_entry_set(&msrs[n++], MSR_KVM_ASYNC_PF_EN, env->async_pf_en_msr);
+#endif
     }
 #ifdef KVM_CAP_MCE
     if (env->mcg_cap) {

@@ -1064,6 +1070,9 @@ static int kvm_get_msrs(CPUState *env)
 #endif
     msrs[n++].index = MSR_KVM_SYSTEM_TIME;
     msrs[n++].index = MSR_KVM_WALL_CLOCK;
+#ifdef KVM_CAP_ASYNC_PF
+    msrs[n++].index = MSR_KVM_ASYNC_PF_EN;
+#endif
 
 #ifdef KVM_CAP_MCE
     if (env->mcg_cap) {

@@ -1135,6 +1144,11 @@ static int kvm_get_msrs(CPUState *env)
             }
 #endif
             break;
+#ifdef KVM_CAP_ASYNC_PF
+        case MSR_KVM_ASYNC_PF_EN:
+            env->async_pf_en_msr = msrs[i].data;
+            break;
+#endif
         }
     }
 

index 5f8376c..d78eceb 100644
@@ -373,6 +373,24 @@ static int cpu_post_load(void *opaque, int version_id)
     return 0;
 }
 
+static bool async_pf_msr_needed(void *opaque)
+{
+    CPUState *cpu = opaque;
+
+    return cpu->async_pf_en_msr != 0;
+}
+
+static const VMStateDescription vmstate_async_pf_msr = {
+    .name = "cpu/async_pf_msr",
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .minimum_version_id_old = 1,
+    .fields      = (VMStateField []) {
+        VMSTATE_UINT64(async_pf_en_msr, CPUState),
+        VMSTATE_END_OF_LIST()
+    }
+};
+
 static const VMStateDescription vmstate_cpu = {
     .name = "cpu",
     .version_id = CPU_SAVE_VERSION,

@@ -475,6 +493,14 @@ static const VMStateDescription vmstate_cpu = {
         VMSTATE_YMMH_REGS_VARS(ymmh_regs, CPUState, CPU_NB_REGS, 12),
         VMSTATE_END_OF_LIST()
         /* The above list is not sorted /wrt version numbers, watch out! */
+    },
+    .subsections = (VMStateSubsection []) {
+        {
+            .vmsd = &vmstate_async_pf_msr,
+            .needed = async_pf_msr_needed,
+        } , {
+            /* empty */
+        }
     }
 };