memory: introduce memory_region_set_alias_offset()

Add an API to update an alias offset of an active alias.  This can be
used to simplify implementation of dynamic memory banks.

Signed-off-by: Avi Kivity <avi@redhat.com>

memory.c

@@ -1345,6 +1345,20 @@ void memory_region_set_address(MemoryRegion *mr, target_phys_addr_t addr)
     memory_region_transaction_commit();
 }
 
+void memory_region_set_alias_offset(MemoryRegion *mr, target_phys_addr_t offset)
+{
+    target_phys_addr_t old_offset = mr->alias_offset;
+
+    assert(mr->alias);
+    mr->alias_offset = offset;
+
+    if (offset == old_offset || !mr->parent) {
+        return;
+    }
+
+    memory_region_update_topology(mr);
+}
+
 void set_system_memory_map(MemoryRegion *mr)
 {
     address_space_memory.root = mr;

memory.h

@@ -529,6 +529,18 @@ void memory_region_set_enabled(MemoryRegion *mr, bool enabled);
  */
 void memory_region_set_address(MemoryRegion *mr, target_phys_addr_t addr);
 
+/*
+ * memory_region_set_alias_offset: dynamically update a memory alias's offset
+ *
+ * Dynamically updates the offset into the target region that an alias points
+ * to, as if the fourth argument to memory_region_init_alias() has changed.
+ *
+ * @mr: the #MemoryRegion to be updated; should be an alias.
+ * @offset: the new offset into the target memory region
+ */
+void memory_region_set_alias_offset(MemoryRegion *mr,
+                                    target_phys_addr_t offset);
+
 /* Start a transaction; changes will be accumulated and made visible only
  * when the transaction ends.
  */