exec: make address spaces 64-bit wide

As an alternative to commit 818f86b (exec: limit system memory
size, 2013-11-04) let's just make all address spaces 64-bit wide.
This eliminates problems with phys_page_find ignoring bits above
TARGET_PHYS_ADDR_SPACE_BITS and address_space_translate_internal
consequently messing up the computations.

In Luiz's reported crash, at startup gdb attempts to read from address
0xffffffffffffffe6 to 0xffffffffffffffff inclusive.  The region it gets
is the newly introduced master abort region, which is as big as the PCI
address space (see pci_bus_init).  Due to a typo that's only 2^63-1,
not 2^64.  But we get it anyway because phys_page_find ignores the upper
bits of the physical address.  In address_space_translate_internal then

    diff = int128_sub(section->mr->size, int128_make64(addr));
    *plen = int128_get64(int128_min(diff, int128_make64(*plen)));

diff becomes negative, and int128_get64 booms.

The size of the PCI address space region should be fixed anyway.

Reported-by: Luiz Capitulino <lcapitulino@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

exec.c

@@ -94,7 +94,7 @@ struct PhysPageEntry {
 #define PHYS_MAP_NODE_NIL (((uint32_t)~0) >> 6)
 
 /* Size of the L2 (and L3, etc) page tables.  */
-#define ADDR_SPACE_BITS TARGET_PHYS_ADDR_SPACE_BITS
+#define ADDR_SPACE_BITS 64
 
 #define P_L2_BITS 10
 #define P_L2_SIZE (1 << P_L2_BITS)
@@ -1861,11 +1861,7 @@ static void memory_map_init(void)
 {
     system_memory = g_malloc(sizeof(*system_memory));
 
-    assert(ADDR_SPACE_BITS <= 64);
-
-    memory_region_init(system_memory, NULL, "system",
-                       ADDR_SPACE_BITS == 64 ?
-                       UINT64_MAX : (0x1ULL << ADDR_SPACE_BITS));
+    memory_region_init(system_memory, NULL, "system", UINT64_MAX);
     address_space_init(&address_space_memory, system_memory, "memory");
 
     system_io = g_malloc(sizeof(*system_io));