Software-defined CPU-modes

In recent years, CPU manufacturers have introduced additional op-
erating modes to their CPUs, in addition to privileged and unprivileged
modes, like Intel SGX or ARM Trustzone. These modes are all imple-
mented in hardware and are therefore need to be taken as is to the op-
erating system and applications. This development raises the question of
whether it is possible to define such modes in software and what challenges
are associated with this approach.
One approach to this problem could be the introduction of an so
called ”Mode-Switch-Mode”. This approach envisions a single hardware-
provided mode, called the Mode-Switch Mode,responsible for transitioning
between other modes. Whenever a transition occurs, the CPU switches
to the Mode-Switch Mode, which configures the CPU to enter the desired
mode.
In this presentation, I will explain the concept of this ”Mode-Switch-
Mode” in detail and discuss some of the difficulties which occurred while
trying to implement it in the gem5 simulator.

(Status Talk Beleg)