Add cpu_address_space_init to enforce the invariant that cpu->num_ases
is set exactly once, preventing bypass of the Address Space API.

Signed-off-by: Gustavo Romero <gustavo.romero@linaro.org>
---
 include/exec/cpu-common.h | 19 ++++++++++++++++---
 system/physmem.c          |  8 ++++++++
 2 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/include/exec/cpu-common.h b/include/exec/cpu-common.h
index 126f645354..1ab63eac9f 100644
--- a/include/exec/cpu-common.h
+++ b/include/exec/cpu-common.h
@@ -101,6 +101,19 @@ int qemu_ram_get_fd(RAMBlock *rb);
 size_t qemu_ram_pagesize(RAMBlock *block);
 size_t qemu_ram_pagesize_largest(void);
 
+
+/**
+ * cpu_address_space_init:
+ * @cpu: CPU to init the number of address space(s)
+ * @num_ases: number of address space(s) in @cpu
+ *
+ * This function must be called before calling cpu_address_space_add and
+ * it sets the total number of address spaces that can be added to @cpu
+ * using cpu_address_space_add.
+ *
+ */
+void cpu_address_space_init(CPUState *cpu, int num_ases);
+
 /**
  * cpu_address_space_add:
  * @cpu: CPU to add this address space to
@@ -114,9 +127,9 @@ size_t qemu_ram_pagesize_largest(void);
  * The target-specific code which registers ASes is responsible
  * for defining what semantics address space 0, 1, 2, etc have.
  *
- * Before the first call to this function, the caller must set
- * cpu->num_ases to the total number of address spaces it needs
- * to support.
+ * Before the first call to this function, the caller must call
+ * cpu_address_space_init to set the total number of address
+ * spaces @cpu can support.
  *
  * Note that with KVM only one address space is supported.
  */
diff --git a/system/physmem.c b/system/physmem.c
index 4a0c1b74f1..2666dbc272 100644
--- a/system/physmem.c
+++ b/system/physmem.c
@@ -775,6 +775,14 @@ hwaddr memory_region_section_get_iotlb(CPUState *cpu,
 
 #endif /* CONFIG_TCG */
 
+void cpu_address_space_init(CPUState *cpu, int num_ases)
+{
+    assert(num_ases > 0);
+    assert(cpu->num_ases == 0);
+
+    cpu->num_ases = num_ases;
+}
+
 void cpu_address_space_add(CPUState *cpu, int asidx,
                            const char *prefix, MemoryRegion *mr)
 {
-- 
2.34.1