x86/speculation/l1tf: Make pmd/pud_mknotpresent() invert

x86/speculation/l1tf: Make pmd/pud_mknotpresent() invert

commit 0768f91530ff46683e0b372df14fd79fe8d156e5 upstream.

Some cases in THP like:
  - MADV_FREE
  - mprotect
  - split

mark the PMD non present for temporarily to prevent races. The window for
an L1TF attack in these contexts is very small, but it wants to be fixed
for correctness sake.

Use the proper low level functions for pmd/pud_mknotpresent() to address
this.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
[bwh: Backported to 3.16:
 - Drop change to pud_mknotpresent()
 - pmd_mknotpresent() does not touch _PAGE_NONE]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>