memory: Make memory_region_is_mapped() succeed when mapped via an alias

memory_region_is_mapped() currently does not return "true" when a memory
region is mapped via an alias.

Assuming we have:
    alias (A0) -> alias (A1) -> region (R0)
Mapping A0 would currently only make memory_region_is_mapped() succeed
on A0, but not on A1 and R0.

Let's fix that by adding a "mapped_via_alias" counter to memory regions and
updating it accordingly when an alias gets (un)mapped.

I am not aware of actual issues, this is rather a cleanup to make it
consistent.

Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20211102164317.45658-3-david@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>

2 files changed, 13 insertions, 1 deletions

diff --git a/include/exec/memory.h b/include/exec/memory.h
index 20f1b27377..fea1a493b9 100644
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -738,6 +738,7 @@ struct MemoryRegion {
     const MemoryRegionOps *ops;
     void *opaque;
     MemoryRegion *container;
+    int mapped_via_alias; /* Mapped via an alias, container might be NULL */
     Int128 size;
     hwaddr addr;
     void (*destructor)(MemoryRegion *mr);
diff --git a/softmmu/memory.c b/softmmu/memory.c
index 5e69624f7f..e37a4b8ae3 100644
--- a/softmmu/memory.c
+++ b/softmmu/memory.c
@@ -2545,8 +2545,13 @@ static void memory_region_add_subregion_common(MemoryRegion *mr,
                                                hwaddr offset,
                                                MemoryRegion *subregion)
 {
+    MemoryRegion *alias;
+
     assert(!subregion->container);
     subregion->container = mr;
+    for (alias = subregion->alias; alias; alias = alias->alias) {
+        alias->mapped_via_alias++;
+    }
     subregion->addr = offset;
     memory_region_update_container_subregions(subregion);
 }
@@ -2571,9 +2576,15 @@ void memory_region_add_subregion_overlap(MemoryRegion *mr,
 void memory_region_del_subregion(MemoryRegion *mr,
                                  MemoryRegion *subregion)
 {
+    MemoryRegion *alias;
+
     memory_region_transaction_begin();
     assert(subregion->container == mr);
     subregion->container = NULL;
+    for (alias = subregion->alias; alias; alias = alias->alias) {
+        alias->mapped_via_alias--;
+        assert(alias->mapped_via_alias >= 0);
+    }
     QTAILQ_REMOVE(&mr->subregions, subregion, subregions_link);
     memory_region_unref(subregion);
     memory_region_update_pending |= mr->enabled && subregion->enabled;
@@ -2670,7 +2681,7 @@ static FlatRange *flatview_lookup(FlatView *view, AddrRange addr)
 
 bool memory_region_is_mapped(MemoryRegion *mr)
 {
-    return mr->container ? true : false;
+    return !!mr->container || mr->mapped_via_alias;
 }
 
 /* Same as memory_region_find, but it does not add a reference to the