alderlake crashes (random memory corruption?) with 6.0 i915 / ucode related

[Hans de Goede]

Hi All,

Yesterday I got a new Lenovo ThinkPad X1 yoga gen 7 laptop, since I plan
to make this my new day to day laptop I have copied over the entire
rootfs, /home, etc. from my current laptop to avoid having to tweak
everything to my liking again.

This meant I had an initramfs generated for the other laptop. Which should
be fine since both are Intel machines and the old 5.19.y initramfs-es
worked fine. But 6.0.0 crashed with what seems like random memory
corruption (list integrity checks failing) until I regenerated the initrd ...

Comparing the old vs regenerated initrds showed no relevant differences,
which made me think this is a CPU ucode issue (which is pre-fixed
to the initrd for early microcode loading).

After some tests I have the following obeservations with 6.0.0:

1. The least stable is the old initrd (so with the wrong
ucode prefixed) this crashes before ever reaching gdm.
I believe that this is caused by late microcode loading
kicking in in this case (I though that was being removed?)
and doing load microcode loading on the i7-1260P with its
mix of P + E cores seems to seriously mess things up.

2. Slightly more stable, lasting at least a few minutes
before crashing is using dis_ucode_ldr

3. Using nomodeset seems to stabilize things even with
the old initrd with the wrong microcode prefixed

4. 5.19, with an old initrd and with normal modesetting
enabled works fine, so in a way this is a 6.0.0 regression

5. Using 6.0 with the new initrd with the new microcode
seems mostly stable, although sometimes this seems to 
hang very early during boot, esp. if a previous boot
crashed and I have not run this for a long time yet.

6. After crashes it seems to be necessary to powercycle
the machine to get things back in working condition.


With 6.0 the following WARN triggers:
drivers/gpu/drm/i915/display/intel_bios.c:477:

        drm_WARN(&i915->drm, min_size == 0,
                 "Block %d min_size is zero\n", section_id);

Since nomodeset helps this might be quite relevant, in 5.19.13
this does not happen, but I'm not sure if 5.19 has this check
at all.


There is a 2022/10/07 BIOS update which includes a CPU microcode
update available from Lenovo, I have not applied this yet in case
people want to investigate this further first.

Regards,

Hans