memory: Add MemoryRegionIOMMUOps.notify_started/stopped callbacks

The IOMMU driver may change behavior depending on whether a notifier
client is present.  In the case of POWER, this represents a change in
the visibility of the IOTLB, for other drivers such as intel-iommu and
future AMD-Vi emulation, notifier support is not yet enabled and this
provides the opportunity to flag that incompatibility.
Signed-off-by: NAlexey Kardashevskiy <aik@ozlabs.ru>
Reviewed-by: NDavid Gibson <david@gibson.dropbear.id.au>
Reviewed-by: NPeter Xu <peterx@redhat.com>
Tested-by: NPeter Xu <peterx@redhat.com>
Acked-by: NPaolo Bonzini <pbonzini@redhat.com>
[new log & extracted from [PATCH qemu v17 12/12] spapr_iommu, vfio, memory: Notify IOMMU about starting/stopping listening]
Signed-off-by: NAlex Williamson <alex.williamson@redhat.com>

hw/vfio/common.c

@@ -455,7 +455,8 @@ static void vfio_listener_region_del(MemoryListener *listener,
 
         QLIST_FOREACH(giommu, &container->giommu_list, giommu_next) {
             if (giommu->iommu == section->mr) {
-                memory_region_unregister_iommu_notifier(&giommu->n);
+                memory_region_unregister_iommu_notifier(giommu->iommu,
+                                                        &giommu->n);
                 QLIST_REMOVE(giommu, giommu_next);
                 g_free(giommu);
                 break;
@@ -991,7 +992,7 @@ static void vfio_disconnect_container(VFIOGroup *group)
         QLIST_REMOVE(container, next);
 
         QLIST_FOREACH_SAFE(giommu, &container->giommu_list, giommu_next, tmp) {
-            memory_region_unregister_iommu_notifier(&giommu->n);
+            memory_region_unregister_iommu_notifier(giommu->iommu, &giommu->n);
             QLIST_REMOVE(giommu, giommu_next);
             g_free(giommu);
         }

include/exec/memory.h

@@ -153,6 +153,10 @@ 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);
 };
 
 typedef struct CoalescedMemoryRange CoalescedMemoryRange;
@@ -622,9 +626,11 @@ void memory_region_iommu_replay(MemoryRegion *mr, Notifier *n, bool is_write);
  * memory_region_unregister_iommu_notifier: unregister a notifier for
  * changes to IOMMU translation entries.
  *
+ * @mr: the memory region which was observed and for which notity_stopped()
+ *      needs to be called
  * @n: the notifier to be removed.
  */
-void memory_region_unregister_iommu_notifier(Notifier *n);
+void memory_region_unregister_iommu_notifier(MemoryRegion *mr, Notifier *n);
 
 /**
  * memory_region_name: get a memory region's name

memory.c

@@ -1499,6 +1499,10 @@ bool memory_region_is_logging(MemoryRegion *mr, uint8_t client)
 
 void memory_region_register_iommu_notifier(MemoryRegion *mr, Notifier *n)
 {
+    if (mr->iommu_ops->notify_started &&
+        QLIST_EMPTY(&mr->iommu_notify.notifiers)) {
+        mr->iommu_ops->notify_started(mr);
+    }
     notifier_list_add(&mr->iommu_notify, n);
 }
 
@@ -1532,9 +1536,13 @@ void memory_region_iommu_replay(MemoryRegion *mr, Notifier *n, bool is_write)
     }
 }
 
-void memory_region_unregister_iommu_notifier(Notifier *n)
+void memory_region_unregister_iommu_notifier(MemoryRegion *mr, Notifier *n)
 {
     notifier_remove(n);
+    if (mr->iommu_ops->notify_stopped &&
+        QLIST_EMPTY(&mr->iommu_notify.notifiers)) {
+        mr->iommu_ops->notify_stopped(mr);
+    }
 }
 
 void memory_region_notify_iommu(MemoryRegion *mr,