thp: introduce pmdp_invalidate()

On s390, a valid page table entry must not be changed while it is attached
to any CPU.  So instead of pmd_mknotpresent() and set_pmd_at(), an IDTE
operation would be necessary there.  This patch introduces the
pmdp_invalidate() function, to allow architecture-specific
implementations.

Signed-off-by: Gerald Schaefer <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Hillf Danton <[email protected]>
Cc: Martin Schwidefsky <[email protected]>
Cc: Heiko Carstens <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
index 044939f..ebdd74f 100644
--- a/include/asm-generic/pgtable.h
+++ b/include/asm-generic/pgtable.h
@@ -170,6 +170,11 @@
 extern pgtable_t pgtable_trans_huge_withdraw(struct mm_struct *mm);
 #endif
 
+#ifndef __HAVE_ARCH_PMDP_INVALIDATE
+extern void pmdp_invalidate(struct vm_area_struct *vma, unsigned long address,
+			    pmd_t *pmdp);
+#endif
+
 #ifndef __HAVE_ARCH_PTE_SAME
 static inline int pte_same(pte_t pte_a, pte_t pte_b)
 {