diff --git a/exec.c b/exec.c
index 87b0b39b90..030118e68e 100644
--- a/exec.c
+++ b/exec.c
@@ -854,7 +854,7 @@ static void mem_add(MemoryListener *listener, MemoryRegionSection *section)
         now = remain;
         if (int128_lt(remain.size, page_size)) {
             register_subpage(d, &now);
-        } else if (remain.offset_within_region & ~TARGET_PAGE_MASK) {
+        } else if (remain.offset_within_address_space & ~TARGET_PAGE_MASK) {
             now.size = page_size;
             register_subpage(d, &now);
         } else {
@@ -1805,11 +1805,14 @@ 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);
-    memory_listener_register(&tcg_memory_listener, &address_space_memory);
+    if (tcg_enabled()) {
+        memory_listener_register(&tcg_memory_listener, &address_space_memory);
+    }
 }
 
 MemoryRegion *get_system_memory(void)
@@ -1913,6 +1916,9 @@ static int memory_access_size(MemoryRegion *mr, unsigned l, hwaddr addr)
     if (l > access_size_max) {
         l = access_size_max;
     }
+    if (l & (l - 1)) {
+        l = 1 << (qemu_fls(l) - 1);
+    }
 
     return l;
 }
diff --git a/include/exec/ioport.h b/include/exec/ioport.h
index bdd4e964eb..b3848be684 100644
--- a/include/exec/ioport.h
+++ b/include/exec/ioport.h
@@ -45,6 +45,10 @@ typedef struct MemoryRegionPortio {
 
 #define PORTIO_END_OF_LIST() { }
 
+#ifndef CONFIG_USER_ONLY
+extern const MemoryRegionOps unassigned_io_ops;
+#endif
+
 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 79b7f1ae38..707cce88ab 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 -1ULL;
+}
+
+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);
diff --git a/memory.c b/memory.c
index 886f838951..5a10fd0bde 100644
--- a/memory.c
+++ b/memory.c
@@ -872,7 +872,7 @@ static uint64_t unassigned_mem_read(void *opaque, hwaddr addr,
     if (current_cpu != NULL) {
         cpu_unassigned_access(current_cpu, addr, false, false, 0, size);
     }
-    return -1ULL;
+    return 0;
 }
 
 static void unassigned_mem_write(void *opaque, hwaddr addr,