mmu_notifier: close hole in fork

[Christoph Lameter]

Talking to Robin and Jack we found taht we still have a hole during fork. 
Fork may set a pte writeprotect. At that point the remote pte are 
not marked readonly(!). Remote writes may occur to pages that are marked 
readonly locally without this patch.

mmu_notifier: Provide invalidate_range on fork

On fork we change ptes in cow mappings to readonly. This means we must
invalidate the ptes so that they are reestablished later with proper
permission.

Signed-off-by: Christoph Lameter <clameter@xxxxxxx>

---
 mm/memory.c |    6 ++++++
 1 file changed, 6 insertions(+)

Index: linux-2.6/mm/memory.c
===================================================================
--- linux-2.6.orig/mm/memory.c	2008-01-31 13:42:35.000000000 -0800
+++ linux-2.6/mm/memory.c	2008-01-31 13:47:31.000000000 -0800
@@ -602,6 +602,9 @@ int copy_page_range(struct mm_struct *ds
 	if (is_vm_hugetlb_page(vma))
 		return copy_hugetlb_page_range(dst_mm, src_mm, vma);
 
+	if (is_cow_mapping(vma->vm_flags))
+		mmu_notifier(invalidate_range_begin, src_mm, addr, end, 0);
+
 	dst_pgd = pgd_offset(dst_mm, addr);
 	src_pgd = pgd_offset(src_mm, addr);
 	do {
@@ -612,6 +615,9 @@ int copy_page_range(struct mm_struct *ds
 						vma, addr, next))
 			return -ENOMEM;
 	} while (dst_pgd++, src_pgd++, addr = next, addr != end);
+
+	if (is_cow_mapping(vma->vm_flags))
+		mmu_notifier(invalidate_range_end, src_mm, 0);
 	return 0;
 }
 
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