After sending the last message, I've done a little more debugging and dumped cr0, and also checked the C7 FCR, everything indicates the cache is properly enabled and not in NoWriteThrough mode, although I have very little C7 specific information and none of it relating to cache.

So, I'm now looking elsewhere, and at the moment I'm looking at MTRRs. All the fixed MTRRs, under coreboot, are 0'd out, and variable are all type 6 (WB?), as can be seen in the attached boot log. Here's the way the stock BIOS sets them up:

# IA32_MTRR_FIX64K_00000 0x00000250 = 0x0606060606060606
# IA32_MTRR_FIX16K_80000 0x00000258 = 0x0606060606060606
# IA32_MTRR_FIX16K_A0000 0x00000259 = 0x0000000000000000
# IA32_MTRR_FIX4K_C0000 0x00000268 = 0x0505050505050505
# IA32_MTRR_FIX4K_C8000 0x00000269 = 0x0000000505050505
# IA32_MTRR_FIX4K_D0000 0x0000026a = 0x0000000000000000
# IA32_MTRR_FIX4K_D8000 0x0000026b = 0x0000000000000000
# IA32_MTRR_FIX4K_E0000 0x0000026c = 0x0000000000000000
# IA32_MTRR_FIX4K_E8000 0x0000026d = 0x0000000000000000
# IA32_MTRR_FIX4K_F0000 0x0000026e = 0x0404040404040404
# IA32_MTRR_FIX4K_F8000 0x0000026f = 0x0404040404040400
root@khan:~/coreboot/util/msrtool# cat /proc/mtrr                              
reg00: base=0x000000000 (    0MB), size= 1024MB, count=1: write-back           
reg01: base=0x03e000000 (  992MB), size=   32MB, count=1: uncachable           
reg02: base=0x0f8000000 ( 3968MB), size=   32MB, count=2: write-combining      
reg03: base=0x03df00000 (  991MB), size=    1MB, count=1: uncachable           
reg04: base=0x0f4000000 ( 3904MB), size=   32MB, count=1: write-combining

I'm frankly not sure if I'm on the right track or not, I've done some work porting chipsets but very little with the CPU itself. Any help would be greatly appreciated, I was hoping this project was "just" writing IRQ and ACPI tables.