Re: Folding _PAGE_PWT into _PAGE_PCD (was Re: unify pagetable accessors patch causes double fault II)

Andi Kleen
2008-01-15T17:20:50Z

> BTW, I just noticed that _PAGE_PWT has been folded into _PAGE_PCD. This
> seems like a really bad idea to me, since it breaks the rule that
> _PAGE_X == 1 << _PAGE_BIT_X. I can't think of a specific place where
> this would cause problems, but this kind of non-uniformity always ends
> up biting someone in the arse.

Agreed that it's a bad idea.

>
> I think having a specific _PAGE_NOCACHE which combines these bits is a
> better approach.

CPA series adds that already

+/* Needs special handling for large pages */
+#define _PAGE_CACHE (_PAGE_PCD|_PAGE_PWT|_PAGE_PAT)
+

-Andi