Re: MPIE and MPP update when returning from interrupt with MRET
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This is in the priv spec sec 220.127.116.11 - just search for mret.
My explanation of why MPP reverts to Umode is to prevent privilege escalation if you go off the end of the 1-deep privilege level stack.
Whichever mode you return to, you can always set PP to either your own mode, or a lower priv level, but not higher, and this ensures it doesn't start out higher.
The absence of which mode you are in is quite deliberate: its existence is a virtualization hole.
On Tue, Dec 15, 2020 at 11:48 AM Richard Trauben <rtrauben@...> wrote: