hw/intc/arm_gic: reserved register addresses are RAZ/WI

The GICv2 specification says that reserved register addresses
must RAZ/WI; now that we implement external abort handling
for Arm CPUs this means we must return MEMTX_OK rather than
MEMTX_ERROR, to avoid generating a spurious guest data abort.

Cc: qemu-stable@nongnu.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 1513183941-24300-3-git-send-email-peter.maydell@linaro.org
Reviewed-by: Alistair Francis <alistair.francis@xilinx.com>

hw/intc/arm_gic.c

@@ -1261,7 +1261,8 @@ static MemTxResult gic_cpu_read(GICState *s, int cpu, int offset,
     default:
         qemu_log_mask(LOG_GUEST_ERROR,
                       "gic_cpu_read: Bad offset %x\n", (int)offset);
-        return MEMTX_ERROR;
+        *data = 0;
+        break;
     }
     return MEMTX_OK;
 }
@@ -1329,7 +1330,7 @@ static MemTxResult gic_cpu_write(GICState *s, int cpu, int offset,
     default:
         qemu_log_mask(LOG_GUEST_ERROR,
                       "gic_cpu_write: Bad offset %x\n", (int)offset);
-        return MEMTX_ERROR;
+        return MEMTX_OK;
     }
     gic_update(s);
     return MEMTX_OK;