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xbox: Make flash ROM memory regions writeable 

In lieu of proper writeback cache emulation, mark the flash ROM memory
region(s) as writeable. This is necessary to enable later Xbox kernel
revisions which write to a single address within this region during very
early startup code and expect the written value to persist when read
back in the next instruction. See comment in patch for more details.
This commit is contained in:
Mike 2020-11-12 00:11:30 -06:00 committed by mborgerson
parent 2955b842f2
commit bdd8375ba2
1 changed files with 16 additions and 2 deletions
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18
hw/xbox/xbox.c
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@ -143,12 +143,26 @@ static void xbox_flash_init(MemoryRegion *rom_memory)
g_free(filename);
}
/* XBOX_FIXME: The "memory_region_set_readonly" calls below have been
* temporarily commented out due to MCPX 1.1-based kernels hanging
* in the first bootloader stage when doing RSA signature verification.
*
* This is caused by code incorrectly using the flash memory range to
* store the following computation; luckily real hardware's writeback
* cache policy (verified against MTRR config) appears to allow this
* to succeed, but qemu's emulation of such isn't capable of this yet
* so the value is never updated in ROM unless readonly is unspecified.
*
* sub ds:0FFFFD52Ch, eax
* mov eax, ds:0FFFFD52Ch
*/
/* Create BIOS region */
MemoryRegion *bios;
bios = g_malloc(sizeof(*bios));
assert(bios != NULL);
memory_region_init_ram(bios, NULL, "xbox.bios", bios_size, &error_fatal);
memory_region_set_readonly(bios, true);
//memory_region_set_readonly(bios, true);
rom_add_blob_fixed("xbox.bios", bios_data, bios_size,
(uint32_t)(-2 * bios_size));
@ -164,7 +178,7 @@ static void xbox_flash_init(MemoryRegion *rom_memory)
MemoryRegion *map_bios = g_malloc(sizeof(*map_bios));
memory_region_init_alias(map_bios, NULL, "pci-bios", bios, 0, bios_size);
memory_region_add_subregion(rom_memory, map_loc, map_bios);
memory_region_set_readonly(map_bios, true);
//memory_region_set_readonly(map_bios, true);
}
}