Didn't they have issues with `LOCK CMPXCHG`(not the 8B)? This is out of my depth and I am not sure, but it sounds similar to the f00f bug.

1: https://en.wikipedia.org/wiki/Intel_Quark#Segfault_bug

Yes, they did have the bug with the lock prefix. IOT people at Microsoft got NT booting on the Quark and we ran into that problem. I wound up writing a small tool to patch out all the lock prefixes.