accel/tcg: Pass read access type through to io_readx()

The io_readx() function needs to know whether the load it is
doing is an MMU_DATA_LOAD or an MMU_INST_FETCH, so that it
can pass the right value to the cpu_transaction_failed()
function. Plumb this information through from the softmmu
code.

This is currently not often going to give the wrong answer,
because usually instruction fetches go via get_page_addr_code().
However once we switch over to handling execution from non-RAM by
creating single-insn TBs, the path for an insn fetch to generate
a bus error will be through cpu_ld*_code() and io_readx(),
so without this change we will generate a d-side fault when we
should generate an i-side fault.

We also have to pass the access type via a CPU struct global
down to unassigned_mem_read(), for the benefit of the targets
which still use the cpu_unassigned_access() hook (m68k, mips,
sparc, xtensa).

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Tested-by: Cédric Le Goater <clg@kaod.org>
Message-id: 20180710160013.26559-2-peter.maydell@linaro.org

include/qom/cpu.h

@@ -386,6 +386,12 @@ struct CPUState {
      */
     uintptr_t mem_io_pc;
     vaddr mem_io_vaddr;
+    /*
+     * This is only needed for the legacy cpu_unassigned_access() hook;
+     * when all targets using it have been converted to use
+     * cpu_transaction_failed() instead it can be removed.
+     */
+    MMUAccessType mem_io_access_type;
 
     int kvm_fd;
     struct KVMState *kvm_state;