exec.c: Fix subpage memory access to RAM MemoryRegion

Commit 95c318f5 (Fix segfault in mmio
subpage handling code.) prevented a segfault by making all subpage
registrations over an existing memory page perform an unassigned access.
Symptoms were writes not taking effect and reads returning zero.

Very small page sizes are not currently supported either,
so subpage memory areas cannot fully be avoided.

Therefore change the previous fix to use a new IO_MEM_SUBPAGE_RAM
instead of IO_MEM_UNASSIGNED. Suggested by Avi.
Reviewed-by: NAvi Kivity <avi@redhat.com>
Signed-off-by: NAndreas Färber <afaerber@suse.de>
Cc: Avi Kivity <avi@redhat.com>
Cc: Gleb Natapov <gleb@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

cpu-common.h

@@ -172,6 +172,7 @@ void cpu_physical_memory_write_rom(target_phys_addr_t addr,
 #define IO_MEM_ROM         (1 << IO_MEM_SHIFT) /* hardcoded offset */
 #define IO_MEM_UNASSIGNED  (2 << IO_MEM_SHIFT)
 #define IO_MEM_NOTDIRTY    (3 << IO_MEM_SHIFT)
+#define IO_MEM_SUBPAGE_RAM (4 << IO_MEM_SHIFT)
 
 /* Acts like a ROM when read and like a device when written.  */
 #define IO_MEM_ROMD        (1)

exec.c

@@ -3570,6 +3570,63 @@ static CPUWriteMemoryFunc * const subpage_write[] = {
     &subpage_writel,
 };
 
+static uint32_t subpage_ram_readb(void *opaque, target_phys_addr_t addr)
+{
+    ram_addr_t raddr = addr;
+    void *ptr = qemu_get_ram_ptr(raddr);
+    return ldub_p(ptr);
+}
+
+static void subpage_ram_writeb(void *opaque, target_phys_addr_t addr,
+                               uint32_t value)
+{
+    ram_addr_t raddr = addr;
+    void *ptr = qemu_get_ram_ptr(raddr);
+    stb_p(ptr, value);
+}
+
+static uint32_t subpage_ram_readw(void *opaque, target_phys_addr_t addr)
+{
+    ram_addr_t raddr = addr;
+    void *ptr = qemu_get_ram_ptr(raddr);
+    return lduw_p(ptr);
+}
+
+static void subpage_ram_writew(void *opaque, target_phys_addr_t addr,
+                               uint32_t value)
+{
+    ram_addr_t raddr = addr;
+    void *ptr = qemu_get_ram_ptr(raddr);
+    stw_p(ptr, value);
+}
+
+static uint32_t subpage_ram_readl(void *opaque, target_phys_addr_t addr)
+{
+    ram_addr_t raddr = addr;
+    void *ptr = qemu_get_ram_ptr(raddr);
+    return ldl_p(ptr);
+}
+
+static void subpage_ram_writel(void *opaque, target_phys_addr_t addr,
+                               uint32_t value)
+{
+    ram_addr_t raddr = addr;
+    void *ptr = qemu_get_ram_ptr(raddr);
+    stl_p(ptr, value);
+}
+
+static CPUReadMemoryFunc * const subpage_ram_read[] = {
+    &subpage_ram_readb,
+    &subpage_ram_readw,
+    &subpage_ram_readl,
+};
+
+static CPUWriteMemoryFunc * const subpage_ram_write[] = {
+    &subpage_ram_writeb,
+    &subpage_ram_writew,
+    &subpage_ram_writel,
+};
+
 static int subpage_register (subpage_t *mmio, uint32_t start, uint32_t end,
                              ram_addr_t memory, ram_addr_t region_offset)
 {
@@ -3583,8 +3640,9 @@ static int subpage_register (subpage_t *mmio, uint32_t start, uint32_t end,
     printf("%s: %p start %08x end %08x idx %08x eidx %08x mem %ld\n", __func__,
            mmio, start, end, idx, eidx, memory);
 #endif
-    if ((memory & ~TARGET_PAGE_MASK) == IO_MEM_RAM)
-        memory = IO_MEM_UNASSIGNED;
+    if ((memory & ~TARGET_PAGE_MASK) == IO_MEM_RAM) {
+        memory = IO_MEM_SUBPAGE_RAM;
+    }
     memory = (memory >> IO_MEM_SHIFT) & (IO_MEM_NB_ENTRIES - 1);
     for (; idx <= eidx; idx++) {
         mmio->sub_io_index[idx] = memory;
@@ -3817,6 +3875,9 @@ static void io_mem_init(void)
     cpu_register_io_memory_fixed(IO_MEM_NOTDIRTY, error_mem_read,
                                  notdirty_mem_write, NULL,
                                  DEVICE_NATIVE_ENDIAN);
+    cpu_register_io_memory_fixed(IO_MEM_SUBPAGE_RAM, subpage_ram_read,
+                                 subpage_ram_write, NULL,
+                                 DEVICE_NATIVE_ENDIAN);
     for (i=0; i<5; i++)
         io_mem_used[i] = 1;