[PATCH 2/2] arm: cacheflush: Fix user split-caching logic

[Steve Capper]

The user split-caching logic in __do_cache_op divides the area to be
flushed into interruptable chunks of size PAGE_SIZE. Unfortunately,
there is no check to see whether or not the range to be flushed is
smaller than the chunk size.

This can result cache flushes for larger ranges than intended,
which can result in the flush failing with a -EFAULT. I've observed
slowdown and failure with the icache-hygiene test from libhugetlbfs.

This patch fixes the problem by replacing chunk with the minimum of
PAGE_SIZE or (end - start), thus we do not overflush.

Signed-off-by: Steve Capper <steve.capper at linaro.org>
---
 arch/arm/kernel/traps.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
index 8fcda14..5d3c455 100644
--- a/arch/arm/kernel/traps.c
+++ b/arch/arm/kernel/traps.c
@@ -503,7 +503,7 @@ static inline int
 __do_cache_op(unsigned long start, unsigned long end)
 {
 	int ret;
-	unsigned long chunk = PAGE_SIZE;
+	unsigned long chunk = min(end - start, PAGE_SIZE);
 
 	do {
 		if (signal_pending(current)) {
-- 
1.8.1.4