[PATCH 1/5] powerpc/mm: only call store_updates_sp() on stores in do_page_fault()

[Christophe Leroy]

Function store_updates_sp() checks whether the faulting
instruction is a store updating r1. Therefore we can limit its calls
to stores exceptions.

This patch is an improvement of commit a7a9dcd882a67 ("powerpc: Avoid
taking a data miss on every userspace instruction miss")

With the same microbenchmark app, run with 500 as argument, on an
MPC885 we get:

Before this patch: 152000 DTLB misses
After this patch:  147000 DTLB misses

Signed-off-by: Christophe Leroy <christophe.leroy at c-s.fr>
---
 arch/powerpc/mm/fault.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index 3a7d580fdc59..67fefb59d40e 100644
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -287,7 +287,7 @@ int do_page_fault(struct pt_regs *regs, unsigned long address,
 	 * can result in fault, which will cause a deadlock when called with
 	 * mmap_sem held
 	 */
-	if (!is_exec && user_mode(regs))
+	if (is_write && user_mode(regs))
 		store_update_sp = store_updates_sp(regs);
 
 	if (user_mode(regs))
-- 
2.12.0