More speculation on exclaves
A reddit post pointed me to some discussion about exclaves in the Asahi Linux IRC chats, and I have been reconsidering feedback from Howard Oakley. In my first post I said:
To make this possible, additional processor privilege levels are required — likely supported by virtualization extensions, Apple specific additions to SPTM, or most likely via ARM’s TrustZone technology.
While I speculated that TrustZone was being used, exclaves may well use the existing SPTM and GXF (Guarded Execution) privilege levels after all. One implication may be that there is no hard reason they couldn't be supported on iPhone 13 and higher, aside from RAM requirements and development effort. Make no mistake these are huge undertakings even for Apple.
CPU Privilege levels
This would leave all the different elements laid out something like this (again, note I am speculating):
Thread Contexts
I have updated my diagram from the first post on the different contexts that threads can be in:
