hugetlbfs: add missing TLB flush to hugetlb_cow()

A cow break on a hugetlbfs page with page_count > 1 will set a new pte with
set_huge_pte_at(), w/o any tlb flush operation.  The old pte will remain in
the tlb and subsequent write access to the page will result in a page fault
loop, for as long as it may take until the tlb is flushed from somewhere else.
 This patch introduces an architecture-specific huge_ptep_clear_flush()
function, which is called before the the set_huge_pte_at() in hugetlb_cow().

ATTENTION: This is just a nop on all architectures for now, the s390
implementation will come with our large page patch later.  Other architectures
should define their own huge_ptep_clear_flush() if needed.

Acked-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: "Luck, Tony" <tony.luck@intel.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index d36e1f11a5f2..262d0a93d2b6 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -892,6 +892,7 @@ static int hugetlb_cow(struct mm_struct *mm, struct vm_area_struct *vma,
         ptep = huge_pte_offset(mm, address & HPAGE_MASK);
         if (likely(pte_same(*ptep, pte))) {
                 /* Break COW */
+                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 */