Michael S (already5chosen.delete@this.yahoo.com) on July 19, 2022 1:00 am wrote:
> Adrian (a.delete@this.acm.org) on July 18, 2022 10:22 pm wrote:
> >
> >
> > The possibility of enabling the MMU in privileged modes is a
> > relatively recent addition to the IBM POWER architecture.
> >
> > I do not remember when this feature has been added, but in any case
> > that was after 2000, while POWER has been introduced in 1990.
> >
>
> I know virtually nothing about system-level architecture of 64-bit PPC/POWER,
> but would be very surprised if the sentence above is true.
> Without knowing facts I would expect privileged-mode MMU to present in very first
> full implementation of PPC64, i.e. Rs64, a.k.a. Apache (October 1997).
>
> > It was probably added for the benefit of the operating systems that were
> > designed to use the MMU inside the kernel, perhaps for Linux support.
> >
>

Maybe you are right and this feature has been added together with the introduction of the 64-bit ISA.

However, I am pretty sure that this feature has been linked to the introduction of the 3rd mode, the hypervisor mode, besides the older supervisor and user modes.

When the hypervisor mode was introduced in POWER, together with Logical Partitioning, the hypervisor mode became the mode which is executed with address translation disabled and which services the interrupts, while the guest operating systems are executed in supervisor mode, typically with address translation enabled.


I do not remember if the hypervisor mode has been introduced since the beginning with the 64-bit mode, but I suspect that it was added only a few years later.

The oldest POWER ISA version that I have at hand is 2.02, from 2005, and by that time it already had the hypervisor mode.