On Sun, Mar 8, 2015 at 11:35 AM, Linus Torvalds
[off-list ref] wrote:

quoted

As a second hack (not to be applied), could we change:

 #define _PAGE_BIT_PROTNONE      _PAGE_BIT_GLOBAL

to:

 #define _PAGE_BIT_PROTNONE      (_PAGE_BIT_GLOBAL+1)

to double check that the position of the bit does not matter?

Agreed. We should definitely try that.

There's a second reason to do that, actually: the __supported_pte_mask
thing, _and_ the pageattr stuff in __split_large_page() etc play games
with _PAGE_GLOBAL. As does drivers/lguest for some reason.

So looking at this all, there's a lot of room for confusion with _PAGE_GLOBAL.

That kind of confusion would certainly explain the whole "the changes
_look_ like they do the same thing, but don't" - because of silly
semantic conflicts with PROTNONE vs GLOBAL.

                                Linus