Subject: [PATCH V3 02/10] powerpc/mm/slice: Fix off-by-1 error when computing slice mask

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Tue, 21 Mar 2017 22:59:52 +0530

For low slice, max addr should be less than 4G. Without limiting this correctly
we will end up with a low slice mask which has 17th bit set. This is not
a problem with the current code because our low slice mask is of type u16. But
in later patch I am switching low slice mask to u64 type and having the 17bit
set result in wrong slice mask which in turn results in mmap failures.

Reviewed-by: Paul Mackerras <[email-masked]>
Signed-off-by: Aneesh Kumar K.V <[email-masked]>
---
 arch/powerpc/mm/slice.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/mm/slice.c b/arch/powerpc/mm/slice.c
index 2b27458902ee..bf150557dba8 100644
--- a/arch/powerpc/mm/slice.c
+++ b/arch/powerpc/mm/slice.c
@@ -83,11 +83,10 @@ static struct slice_mask slice_range_to_mask(unsigned long start,
 	struct slice_mask ret = { 0, 0 };
 
 	if (start < SLICE_LOW_TOP) {
-		unsigned long mend = min(end, SLICE_LOW_TOP);
-		unsigned long mstart = min(start, SLICE_LOW_TOP);
+		unsigned long mend = min(end, (SLICE_LOW_TOP - 1));
 
 		ret.low_slices = (1u << (GET_LOW_SLICE_INDEX(mend) + 1))
-			- (1u << GET_LOW_SLICE_INDEX(mstart));
+			- (1u << GET_LOW_SLICE_INDEX(start));
 	}
 
 	if ((start + len) > SLICE_LOW_TOP)
-- 
2.7.4