Re: Privilege Levels Below User

Paul A. Clayton wrote:

On 6/8/24 1:37 PM, MitchAlsup1 wrote:

EricP wrote:
 

Scott Lurndal wrote:

[snip]

What they found that not only do they not need 4 levels,
it was a pointless overhead to have to constantly switch between them.
(There is a pretty high penalty to switching modes, copying in args,
validating args, doing something usually simple, then switching back,
when it is all the OS's code anyway.)

 VAX was before common era Hypervisors, do you think VAX could have supported secure mode and hypervisor with their 4 levels ??
 But for similar reasons ring 1 and 2 are not used in x86 machines, either. {{NOw, if we could just go back to 1982 and not invent IDTs, and call gates, .....}}

I thought My 66000 had Port Holes that are vaguely similar to
call gates, so rather than "not invent" perhaps invent with better
semantics and a better interface?

I would place them congruent to Load-From and Store-TO PDP-11/70
instructions.
I have since converted to a more Linux friendly MMU structure.
Port Holes can be easily resurrected.

                                   (Though 1982 might have been too
early to implement such. Better perceiving when to wait for the
technology or understanding to implement something better is
presumably one of the skills acquired by long experience as well
as the related what can be implemented to provide the most
attractive/marketable features without excessively limiting future
developments.

             Letting a competitor provide a temporarily better
product — or delaying entry into a market expecting a feature —
can sometimes be sensible if one expects to leapfrog with
a better long-term alternative, but "worse is better" has some
truth.)

It seems that in terms of computer architectures, the world is
not going to beat a path to your door even if you invent a
better mousetrap.