mmu_notifier: Provide invalidate_range for move_page_tables

Move page tables also needs to invalidate the external references
and hold new references off while moving page table entries.

This is already guaranteed by holding a writelock
on mmap_sem for get_user_pages() but follow_page is not subject to
the mmap_sem locking.

Signed-off-by: Christoph Lameter <clameter@sgi.com>

---
 mm/mremap.c |    4 ++++
 1 file changed, 4 insertions(+)

Index: linux-2.6/mm/mremap.c
===================================================================
--- linux-2.6.orig/mm/mremap.c	2008-01-25 14:25:31.000000000 -0800
+++ linux-2.6/mm/mremap.c	2008-01-31 17:54:19.000000000 -0800
@@ -18,6 +18,7 @@
 #include <linux/highmem.h>
 #include <linux/security.h>
 #include <linux/syscalls.h>
+#include <linux/mmu_notifier.h>
 
 #include <asm/uaccess.h>
 #include <asm/cacheflush.h>
@@ -130,6 +131,8 @@ unsigned long move_page_tables(struct vm
 	old_end = old_addr + len;
 	flush_cache_range(vma, old_addr, old_end);
 
+	mmu_notifier(invalidate_range_begin, vma->vm_mm,
+					old_addr, old_addr + len, 0);
 	for (; old_addr < old_end; old_addr += extent, new_addr += extent) {
 		cond_resched();
 		next = (old_addr + PMD_SIZE) & PMD_MASK;
@@ -150,6 +153,7 @@ unsigned long move_page_tables(struct vm
 		move_ptes(vma, old_pmd, old_addr, old_addr + extent,
 				new_vma, new_pmd, new_addr);
 	}
+	mmu_notifier(invalidate_range_end, vma->vm_mm, 0);
 
 	return len + old_addr - old_end;	/* how much done */
 }