Bug in hugetlb_cow()?

[Doug Doan <dougd@cray.com>]

Hi,

I'm working on a driver that relies on mmu notifications, and found that it is 
lacking for huge pages.

 From handle_mm_fault(),

If we take the normal page path, this is what happens:

handle_pte_fault -> do_wp_page -> ptep_clear_flush_notify -> 
mmu_notifier_invalidate_page

If we're dealing with huge pages, this is what happens:

hugetlb_fault -> hugetlb_cow -> (no mmu notifiers)

Below is my patch, can anyone comment?

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 4c9e6bb..96d9937 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2345,11 +2345,17 @@ retry_avoidcopy:
         ptep = huge_pte_offset(mm, address & huge_page_mask(h));
         if (likely(pte_same(huge_ptep_get(ptep), pte))) {
                 /* Break COW */
+               mmu_notifier_invalidate_range_start(mm,
+                       address & huge_page_mask(h),
+                       (address & huge_page_mask(h)) + huge_page_size(h));
                 huge_ptep_clear_flush(vma, address, ptep);
                 set_huge_pte_at(mm, address, ptep,
                                 make_huge_pte(vma, new_page, 1));
                 /* Make the old page be freed below */
                 new_page = old_page;
+               mmu_notifier_invalidate_range_end(mm,
+                       address & huge_page_mask(h),
+                       (address & huge_page_mask(h)) + huge_page_size(h));
         }
         page_cache_release(new_page);
         page_cache_release(old_page);

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