Definition of x86 _PAGE_SPECIAL and sharing _PAGE_UNUSED1

[Jeremy Fitzhardinge]

_PAGE_SPECIAL is overloading _PAGE_UNUSED1.  Does it really leave
_PAGE_UNUSED1 available for other uses, or does it become an exclusive
user of that flag.  Under what circumstances can they be shared?

arch/x86/mm/pageattr-test.c is now using _PAGE_UNUSED1 as the flag used
to make sure that huge pages are shattered properly (previously it used
_PAGE_GLOBAL).  Is that going to clash with _PAGE_SPECIAL?

In other words, should we drop _PAGE_UNUSED1 altogether, or at least
define how the its different users can coexist?

Am I right in supposing that _PAGE_SPECIAL can only be set on user pages?

(Also, "SPECIAL" is awfully generic.  Was there really no more
descriptive name for this?)

    J
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