Within osfmk/arm/pmap.c what does PPL stand for?

I have looked through the entirety of the 15k lines of code and the corresponding pmap.h and have googled quite a bit but I can't seem to find what PPL stands for. In comments it is talked about alot in the contexts "The PPL" and there are functions with ppl in their names.

PPL = Page Protection Layer

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Quinn “The Eskimo!” @ Developer Technical Support @ Apple
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Within osfmk/arm/pmap.c what does PPL stand for?
 
 
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