[coreboot] ThinkPad X230 with working truncated ME and 11 MB space for payload

[Nico Huber]

Hi Marek,

On 17.04.2017 02:28, Marek Behun wrote:
> So apparently disabling building relocatable kernel fixed the issue
> with kvm.

that seems pretty random.

> 
> But I have now a different issue which renders my X230 useless with
> completely stripped ME. It seems that native ram init does not work
> completely correctly with my RAM modules, or something. When using
> coreboot-master with cleaned ME, at random times applications crash with
> something like
>   BUG: stack guard page was hit at ffff990102a7c000 (stack is
>   ffff990102a78000..ffff990102a7bfff)
> or the system completely freezes. This has more probability of
> happening when the CPU is loaded.
> 
> I have two 8 GiB ram modules:
>   Samsung M471B1G73BH0-CK0 12800S-11-11-F3
>   Elpida EBJ81UG8BBU0-GN-F 12800S-11-10-F3

PC3-12800 is most common...

> 
> They have slightly different parameter (11 vs 10). Could this be the
> problem?

Unlikely.

> 
> I have also tried removing one module, but than the first boot
> (generation of mrc cache) was taking too long (I stopped it at 10
> minutes).
> 
> Any ideas?

Modding the ME firmware is about freedom. The freedom to work around
issues you won't ever see otherwise ;)

What you describe sounds much like random instability (which I'd expect
if RAM training takes that long). Either the system is just unstable
(who knows which fixes you miss if you drop the ME firmware (update))
or something related to the memory controller is off. I have a vague
theory: The ME firmware is sometimes referred to in clock generation
context. Maybe the memory clock is just not the one coreboot thinks it
has configured.

I would try the following to narrow it down: Run the memory training
with the original ME firmware; keep the MRC cache intact while switching
to the truncated ME firmware; boot. If it doesn't work with the cached
values, something around the memory clock might be off. If you have de-
bug access, you could also directly compare the training results from
a boot with the original ME firmware vs. the modded firmware. If not
you can still compare the results from MRC-cache dumps. But you'd have
to decode them first...

Nico