[PULL,28/31] boards.h: Define new flag ignore_memory_transaction_failures

diff --git a/include/hw/boards.h b/include/hw/boards.h
index 3363dd1..7f044d1 100644
--- a/include/hw/boards.h
+++ b/include/hw/boards.h
@@ -131,6 +131,16 @@  typedef struct {
  *    size than the target architecture's minimum. (Attempting to create
  *    such a CPU will fail.) Note that changing this is a migration
  *    compatibility break for the machine.
+ * @ignore_memory_transaction_failures:
+ *    If this is flag is true then the CPU will ignore memory transaction
+ *    failures which should cause the CPU to take an exception due to an
+ *    access to an unassigned physical address; the transaction will instead
+ *    return zero (for a read) or be ignored (for a write). This should be
+ *    set only by legacy board models which rely on the old RAZ/WI behaviour
+ *    for handling devices that QEMU does not yet model. New board models
+ *    should instead use "unimplemented-device" for all memory ranges where
+ *    the guest will attempt to probe for a device that QEMU doesn't
+ *    implement and a stub device is required.
  */
 struct MachineClass {
     /*< private >*/
@@ -171,6 +181,7 @@  struct MachineClass {
     bool rom_file_has_mr;
     int minimum_page_bits;
     bool has_hotpluggable_cpus;
+    bool ignore_memory_transaction_failures;
     int numa_mem_align_shift;
     void (*numa_auto_assign_ram)(MachineClass *mc, NodeInfo *nodes,
                                  int nb_nodes, ram_addr_t size);
diff --git a/include/qom/cpu.h b/include/qom/cpu.h
index 08bd868..995a7be 100644
--- a/include/qom/cpu.h
+++ b/include/qom/cpu.h
@@ -312,6 +312,9 @@  struct qemu_work_item;
  * @trace_dstate_delayed: Delayed changes to trace_dstate (includes all changes
  *                        to @trace_dstate).
  * @trace_dstate: Dynamic tracing state of events for this vCPU (bitmask).
+ * @ignore_memory_transaction_failures: Cached copy of the MachineState
+ *    flag of the same name: allows the board to suppress calling of the
+ *    CPU do_transaction_failed hook function.
  *
  * State of one CPU core or thread.
  */
@@ -398,6 +401,8 @@  struct CPUState {
      */
     bool throttle_thread_scheduled;
 
+    bool ignore_memory_transaction_failures;
+
     /* Note that this is accessed at the start of every TB via a negative
        offset from AREG0.  Leave this field at the end so as to make the
        (absolute value) offset as small as possible.  This reduces code
@@ -864,7 +869,7 @@  static inline void cpu_transaction_failed(CPUState *cpu, hwaddr physaddr,
 {
     CPUClass *cc = CPU_GET_CLASS(cpu);
 
-    if (cc->do_transaction_failed) {
+    if (!cpu->ignore_memory_transaction_failures && cc->do_transaction_failed) {
         cc->do_transaction_failed(cpu, physaddr, addr, size, access_type,
                                   mmu_idx, attrs, response, retaddr);
     }
diff --git a/qom/cpu.c b/qom/cpu.c
index deb8880..dc5392d 100644
--- a/qom/cpu.c
+++ b/qom/cpu.c
@@ -29,6 +29,7 @@ 
 #include "exec/cpu-common.h"
 #include "qemu/error-report.h"
 #include "sysemu/sysemu.h"
+#include "hw/boards.h"
 #include "hw/qdev-properties.h"
 #include "trace-root.h"
 
@@ -363,6 +364,21 @@  static void cpu_common_parse_features(const char *typename, char *features,
 static void cpu_common_realizefn(DeviceState *dev, Error **errp)
 {
     CPUState *cpu = CPU(dev);
+    Object *machine = qdev_get_machine();
+
+    /* qdev_get_machine() can return something that's not TYPE_MACHINE
+     * if this is one of the user-only emulators; in that case there's
+     * no need to check the ignore_memory_transaction_failures board flag.
+     */
+    if (object_dynamic_cast(machine, TYPE_MACHINE)) {
+        ObjectClass *oc = object_get_class(machine);
+        MachineClass *mc = MACHINE_CLASS(oc);
+
+        if (mc) {
+            cpu->ignore_memory_transaction_failures =
+                mc->ignore_memory_transaction_failures;
+        }
+    }
 
     if (dev->hotplugged) {
         cpu_synchronize_post_init(cpu);