From: Igor Mammedov <imammedo@redhat.com>

QEMU will crash when device-memory-region-size property is read if ms->device_memory
wasn't initialized yet.

Crash can be reproduced with:
 $QEMU -preconfig -qmp unix:qmp_socket,server,nowait &
 ./scripts/qmp/qom-get -s qmp_socket /machine.device-memory-region-size

Instead of crashing return 0 if ms->device_memory hasn't been initialized.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Message-Id: <1560174635-22602-1-git-send-email-imammedo@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 hw/i386/pc.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index e96360b..552f340 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -2458,7 +2458,11 @@ pc_machine_get_device_memory_region_size(Object *obj, Visitor *v,
                                          Error **errp)
 {
     MachineState *ms = MACHINE(obj);
-    int64_t value = memory_region_size(&ms->device_memory->mr);
+    int64_t value = 0;
+
+    if (ms->device_memory) {
+        value = memory_region_size(&ms->device_memory->mr);
+    }
 
     visit_type_int(v, name, &value, errp);
 }
-- 
1.8.3.1