Rework ptep_set_access_flags and fix sun4c

Some changes done a while ago to avoid pounding on ptep_set_access_flags and
update_mmu_cache in some race situations break sun4c which requires
update_mmu_cache() to always be called on minor faults.

This patch reworks ptep_set_access_flags() semantics, implementations and
callers so that it's now responsible for returning whether an update is
necessary or not (basically whether the PTE actually changed).  This allow
fixing the sparc implementation to always return 1 on sun4c.

[akpm@linux-foundation.org: fixes, cleanups]
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Hugh Dickins <hugh@veritas.com>
Cc: David Miller <davem@davemloft.net>
Cc: Mark Fortescue <mark@mtfhpc.demon.co.uk>
Acked-by: William Lee Irwin III <wli@holomorphy.com>
Cc: "Luck, Tony" <tony.luck@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 6 insertions, 1 deletions

diff --git a/include/asm-s390/pgtable.h b/include/asm-s390/pgtable.h
index 8fe8d42e64c..0a307bb2f35 100644
--- a/include/asm-s390/pgtable.h
+++ b/include/asm-s390/pgtable.h
@@ -744,7 +744,12 @@ ptep_establish(struct vm_area_struct *vma,
 }
 
 #define ptep_set_access_flags(__vma, __address, __ptep, __entry, __dirty) \
-        ptep_establish(__vma, __address, __ptep, __entry)
+({                                                                        \
+        int __changed = !pte_same(*(__ptep), __entry);                    \
+        if (__changed)                                                    \
+                ptep_establish(__vma, __address, __ptep, __entry);        \
+        __changed;                                                        \
+})
 
 /*
  * Test and clear dirty bit in storage key.