[PATCH v2 10/11] hw/board: Only allow TCG accelerator by default

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

By default machines can only use the TCG and QTest accelerators.

If a machine can use another accelerator, it has to explicitly
list it in its MachineClass valid_accelerators[].

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
---
 include/hw/boards.h | 4 ++--
 hw/core/machine.c   | 8 ++++----
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/include/hw/boards.h b/include/hw/boards.h
index 4d08bc12093..b93d290b348 100644
--- a/include/hw/boards.h
+++ b/include/hw/boards.h
@@ -146,8 +146,8 @@ typedef struct {
  * @valid_accelerators:
  *    If this machine supports a specific set of virtualization accelerators,
  *    this contains a NULL-terminated list of the accelerators that can be
- *    used. If this field is not set, any accelerator is valid. The QTest
- *    accelerator is always valid.
+ *    used. If this field is not set, a default list containing only the TCG
+ *    accelerator is used. The QTest accelerator is always valid.
  * @kvm_type:
  *    Return the type of KVM corresponding to the kvm-type string option or
  *    computed based on other criteria such as the host kernel capabilities
diff --git a/hw/core/machine.c b/hw/core/machine.c
index c42d8e382b1..ca7c9ee2a0c 100644
--- a/hw/core/machine.c
+++ b/hw/core/machine.c
@@ -520,11 +520,11 @@ static void machine_set_nvdimm_persistence(Object *obj, const char *value,
 
 bool machine_class_valid_for_accelerator(MachineClass *mc, const char *acc_name)
 {
-    const char *const *name = mc->valid_accelerators;
+    static const char *const default_accels[] = {
+        "tcg", NULL
+    };
+    const char *const *name = mc->valid_accelerators ? : default_accels;
 
-    if (!name) {
-        return true;
-    }
     if (strcmp(acc_name, "qtest") == 0) {
         return true;
     }
-- 
2.26.2