[Qemu-devel] [PATCH 1/2] memory: Provide separate handling of unassigned io ports accesses

[Jan Kiszka <jan.kiszka@web.de>]

From: Jan Kiszka <jan.kiszka@siemens.com>

Accesses to unassigned io ports shall return -1 on read and be ignored
on write. Ensure these properties via dedicated ops, decoupling us from
the memory core's handling of unassigned accesses.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---
 exec.c                |    3 ++-
 include/exec/ioport.h |    2 ++
 ioport.c              |   16 ++++++++++++++++
 3 files changed, 20 insertions(+), 1 deletions(-)

diff --git a/exec.c b/exec.c
index 3ca9381..9ed598f 100644
--- a/exec.c
+++ b/exec.c
@@ -1820,7 +1820,8 @@ static void memory_map_init(void)
     address_space_init(&address_space_memory, system_memory, "memory");
 
     system_io = g_malloc(sizeof(*system_io));
-    memory_region_init(system_io, NULL, "io", 65536);
+    memory_region_init_io(system_io, NULL, &unassigned_io_ops, NULL, "io",
+                          65536);
     address_space_init(&address_space_io, system_io, "I/O");
 
     memory_listener_register(&core_memory_listener, &address_space_memory);
diff --git a/include/exec/ioport.h b/include/exec/ioport.h
index bdd4e96..84f7f85 100644
--- a/include/exec/ioport.h
+++ b/include/exec/ioport.h
@@ -45,6 +45,8 @@ typedef struct MemoryRegionPortio {
 
 #define PORTIO_END_OF_LIST() { }
 
+extern const MemoryRegionOps unassigned_io_ops;
+
 void cpu_outb(pio_addr_t addr, uint8_t val);
 void cpu_outw(pio_addr_t addr, uint16_t val);
 void cpu_outl(pio_addr_t addr, uint32_t val);
diff --git a/ioport.c b/ioport.c
index 79b7f1a..9765588 100644
--- a/ioport.c
+++ b/ioport.c
@@ -44,6 +44,22 @@ typedef struct MemoryRegionPortioList {
     MemoryRegionPortio ports[];
 } MemoryRegionPortioList;
 
+static uint64_t unassigned_io_read(void *opaque, hwaddr addr, unsigned size)
+{
+    return -1UL;
+}
+
+static void unassigned_io_write(void *opaque, hwaddr addr, uint64_t val,
+                                unsigned size)
+{
+}
+
+const MemoryRegionOps unassigned_io_ops = {
+    .read = unassigned_io_read,
+    .write = unassigned_io_write,
+    .endianness = DEVICE_NATIVE_ENDIAN,
+};
+
 void cpu_outb(pio_addr_t addr, uint8_t val)
 {
     LOG_IOPORT("outb: %04"FMT_pioaddr" %02"PRIx8"\n", addr, val);
-- 
1.7.3.4