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, 12 insertions, 5 deletions

diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
index dc8f99ee305f..7d7bcf990e99 100644
--- a/include/asm-generic/pgtable.h
+++ b/include/asm-generic/pgtable.h
@@ -27,13 +27,20 @@ do {				  					\
  * Largely same as above, but only sets the access flags (dirty,
  * accessed, and writable). Furthermore, we know it always gets set
  * to a "more permissive" setting, which allows most architectures
- * to optimize this.
+ * to optimize this. We return whether the PTE actually changed, which
+ * in turn instructs the caller to do things like update__mmu_cache.
+ * This used to be done in the caller, but sparc needs minor faults to
+ * force that call on sun4c so we changed this macro slightly
  */
 #define ptep_set_access_flags(__vma, __address, __ptep, __entry, __dirty) \
-do {                                                                      \
-        set_pte_at((__vma)->vm_mm, (__address), __ptep, __entry);         \
-        flush_tlb_page(__vma, __address);                                 \
-} while (0)
+({                                                                        \
+        int __changed = !pte_same(*(__ptep), __entry);                    \
+        if (__changed) {                                                  \
+                set_pte_at((__vma)->vm_mm, (__address), __ptep, __entry); \
+                flush_tlb_page(__vma, __address);                         \
+        }                                                                 \
+        __changed;                                                        \
+})
 #endif
 
 #ifndef __HAVE_ARCH_PTEP_TEST_AND_CLEAR_YOUNG