memory: Define API for MemoryRegionOps to take attrs and return status

Define an API so that devices can register MemoryRegionOps whose read
and write callback functions are passed an arbitrary pointer to some
transaction attributes and can return a success-or-failure status code.
This will allow us to model devices which:
 * behave differently for ARM Secure/NonSecure memory accesses
 * behave differently for privileged/unprivileged accesses
 * may return a transaction failure (causing a guest exception)
   for erroneous accesses

This patch defines the new API and plumbs the attributes parameter through
to the memory.c public level functions io_mem_read() and io_mem_write(),
where it is currently dummied out.

The success/failure response indication is also propagated out to
io_mem_read() and io_mem_write(), which retain the old-style
boolean true-for-error return.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>

include/exec/memory.h

@@ -28,6 +28,7 @@
 #ifndef CONFIG_USER_ONLY
 #include "exec/hwaddr.h"
 #endif
+#include "exec/memattrs.h"
 #include "qemu/queue.h"
 #include "qemu/int128.h"
 #include "qemu/notify.h"
@@ -68,6 +69,16 @@ struct IOMMUTLBEntry {
     IOMMUAccessFlags perm;
 };
 
+/* New-style MMIO accessors can indicate that the transaction failed.
+ * A zero (MEMTX_OK) response means success; anything else is a failure
+ * of some kind. The memory subsystem will bitwise-OR together results
+ * if it is synthesizing an operation from multiple smaller accesses.
+ */
+#define MEMTX_OK 0
+#define MEMTX_ERROR             (1U << 0) /* device returned an error */
+#define MEMTX_DECODE_ERROR      (1U << 1) /* nothing at that address */
+typedef uint32_t MemTxResult;
+
 /*
  * Memory region callbacks
  */
@@ -84,6 +95,17 @@ struct MemoryRegionOps {
                   uint64_t data,
                   unsigned size);
 
+    MemTxResult (*read_with_attrs)(void *opaque,
+                                   hwaddr addr,
+                                   uint64_t *data,
+                                   unsigned size,
+                                   MemTxAttrs attrs);
+    MemTxResult (*write_with_attrs)(void *opaque,
+                                    hwaddr addr,
+                                    uint64_t data,
+                                    unsigned size,
+                                    MemTxAttrs attrs);
+
     enum device_endian endianness;
     /* Guest-visible constraints: */
     struct {