[v2,2/3] memory: generalize iommu_ops.notify_started to notifier_add

diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
index 28c31a2..c6bd8f6 100644
--- a/hw/i386/intel_iommu.c
+++ b/hw/i386/intel_iommu.c
@@ -1974,7 +1974,7 @@  static IOMMUTLBEntry vtd_iommu_translate(MemoryRegion *iommu, hwaddr addr,
     return ret;
 }
 
-static void vtd_iommu_notify_started(MemoryRegion *iommu)
+static void vtd_iommu_notifier_add(MemoryRegion *iommu, IOMMUNotifier *n)
 {
     VTDAddressSpace *vtd_as = container_of(iommu, VTDAddressSpace, iommu);
 
@@ -2348,7 +2348,7 @@  static void vtd_init(IntelIOMMUState *s)
     memset(s->womask, 0, DMAR_REG_SIZE);
 
     s->iommu_ops.translate = vtd_iommu_translate;
-    s->iommu_ops.notify_started = vtd_iommu_notify_started;
+    s->iommu_ops.notifier_add = vtd_iommu_notifier_add;
     s->root = 0;
     s->root_extended = false;
     s->dmar_enabled = false;
diff --git a/hw/ppc/spapr_iommu.c b/hw/ppc/spapr_iommu.c
index 6bc4d4d..84421e0 100644
--- a/hw/ppc/spapr_iommu.c
+++ b/hw/ppc/spapr_iommu.c
@@ -156,14 +156,20 @@  static uint64_t spapr_tce_get_min_page_size(MemoryRegion *iommu)
     return 1ULL << tcet->page_shift;
 }
 
-static void spapr_tce_notify_started(MemoryRegion *iommu)
+static void spapr_tce_notifier_add(MemoryRegion *iommu, IOMMUNotifier *n)
 {
-    spapr_tce_set_need_vfio(container_of(iommu, sPAPRTCETable, iommu), true);
+    sPAPRTCETable *tcet = container_of(iommu, sPAPRTCETable, iommu);
+    if (tcet->iommu_users++ == 0) {
+        spapr_tce_set_need_vfio(tcet, true);
+    }
 }
 
-static void spapr_tce_notify_stopped(MemoryRegion *iommu)
+static void spapr_tce_notifier_del(MemoryRegion *iommu)
 {
-    spapr_tce_set_need_vfio(container_of(iommu, sPAPRTCETable, iommu), false);
+    sPAPRTCETable *tcet = container_of(iommu, sPAPRTCETable, iommu);
+    if (--tcet->iommu_users == 0) {
+        spapr_tce_set_need_vfio(tcet, false);
+    }
 }
 
 static int spapr_tce_table_post_load(void *opaque, int version_id)
@@ -246,8 +252,8 @@  static const VMStateDescription vmstate_spapr_tce_table = {
 static MemoryRegionIOMMUOps spapr_iommu_ops = {
     .translate = spapr_tce_translate_iommu,
     .get_min_page_size = spapr_tce_get_min_page_size,
-    .notify_started = spapr_tce_notify_started,
-    .notify_stopped = spapr_tce_notify_stopped,
+    .notifier_add = spapr_tce_notifier_add,
+    .notifier_del = spapr_tce_notifier_del,
 };
 
 static int spapr_tce_table_realize(DeviceState *dev)
diff --git a/include/exec/memory.h b/include/exec/memory.h
index 52914c1..3a2e7d8 100644
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -174,10 +174,10 @@  struct MemoryRegionIOMMUOps {
     IOMMUTLBEntry (*translate)(MemoryRegion *iommu, hwaddr addr, bool is_write);
     /* Returns minimum supported page size */
     uint64_t (*get_min_page_size)(MemoryRegion *iommu);
-    /* Called when the first notifier is set */
-    void (*notify_started)(MemoryRegion *iommu);
-    /* Called when the last notifier is removed */
-    void (*notify_stopped)(MemoryRegion *iommu);
+    /* Called when someone registers to the notify list */
+    void (*notifier_add)(MemoryRegion *iommu, IOMMUNotifier *n);
+    /* Called when someone unregisters from the notify list */
+    void (*notifier_del)(MemoryRegion *iommu, IOMMUNotifier *n);
 };
 
 typedef struct CoalescedMemoryRange CoalescedMemoryRange;
diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
index caf7be9..08627ec 100644
--- a/include/hw/ppc/spapr.h
+++ b/include/hw/ppc/spapr.h
@@ -564,6 +564,7 @@  struct sPAPRTCETable {
     MemoryRegion root, iommu;
     struct VIOsPAPRDevice *vdev; /* for @bypass migration compatibility only */
     QLIST_ENTRY(sPAPRTCETable) list;
+    int iommu_users;
 };
 
 sPAPRTCETable *spapr_tce_find_by_liobn(target_ulong liobn);
diff --git a/memory.c b/memory.c
index f513c5a..a50e627 100644
--- a/memory.c
+++ b/memory.c
@@ -1518,9 +1518,8 @@  void memory_region_register_iommu_notifier(MemoryRegion *mr,
 {
     /* We need to register for at least one bitfield */
     assert(n->notifier_caps != IOMMU_NOTIFIER_NONE);
-    if (mr->iommu_ops->notify_started &&
-        QLIST_EMPTY(&mr->iommu_notify.notifiers)) {
-        mr->iommu_ops->notify_started(mr);
+    if (mr->iommu_ops->notifier_add) {
+        mr->iommu_ops->notifier_add(mr, n);
     }
     notifier_list_add(&mr->iommu_notify, &n->notifier);
 }
@@ -1560,9 +1559,8 @@  void memory_region_unregister_iommu_notifier(MemoryRegion *mr,
                                              IOMMUNotifier *n)
 {
     notifier_remove(&n->notifier);
-    if (mr->iommu_ops->notify_stopped &&
-        QLIST_EMPTY(&mr->iommu_notify.notifiers)) {
-        mr->iommu_ops->notify_stopped(mr);
+    if (mr->iommu_ops->notifier_del) {
+        mr->iommu_ops->notifier_del(mr, n);
     }
 }