boards.h: Define new flag ignore_memory_transaction_failures

Define a new MachineClass field 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.

We need this for ARM boards, where we're about to implement support for
generating external aborts on memory transaction failures. Too many
of our legacy board models rely on the RAZ/WI behaviour and we
would break currently working guests when their "probe for device"
code provoked an external abort rather than a RAZ.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@xilinx.com>
Message-id: 1504626814-23124-2-git-send-email-peter.maydell@linaro.org

1 files changed, 16 insertions, 0 deletions

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);