>I think I mentioned that I believe in "least privilege." I don't want to 
run
>an entire LE/C++ started task in supervisor state. 

When "belief" gets into the way of "function", it could be time to 
re-examine. Perhaps you should look for a way that does not require you to 
be doing key 0 stuff (or conversely does not require you to intermix 
changing between key 0 and key 8 while in problem state)

The prevailing opinion is that avoiding running in key 0 when you can is a 
good thing.
But there is very little concern about running in supervisor state when 
you don't need to (if it makes life easier)

If you want efficiency for your case, then you must use supervisor state.

>After it showed up on a customer's STROBE report, we switched over to 
>using LPSW instead...

If you're unlucky enough to hit the edge case, you will lose the PER bit 
by doing so. There might be other things that could similarly be lost. 
System services are provided for a reason. You bypass them at the 
customer's risk.

>Principle of astonishment
The only thing at all surprising should be, as Charles found, that he 
could not switch back to his "original key". But to accomplish that in 
general would require the system to keep a chain of keys so that you could 
backtrack step by step. We would never do that when the user has a simple 
alternative -- supervisor state. "Least privilege" is a nice guideline, 
but it's not a rule, particularly when you care about performance. If 
you're interested enough to run in key 0, running in supervisor state is a 
small step, not even a leap.

What would have been surprising would be if you switched to key 0 problem 
state and then could not switch between there and key 9 and back since you 
are always supposed to be able to switch to and from key 9.

Peter Relson
z/OS Core Technology Design


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