[V2,02/11] powerpc/mm/slice: when computing slice mask limit lowe slice max addr correctly

Submitted by Aneesh Kumar K.V on March 16, 2017, 10:32 a.m.

Details

Message ID 1489660329-22501-3-git-send-email-aneesh.kumar@linux.vnet.ibm.com
State Superseded
Headers show

Commit Message

Aneesh Kumar K.V March 16, 2017, 10:32 a.m.
For low slice max addr should be less that 4G

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
---
 arch/powerpc/mm/slice.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

Comments

Paul Mackerras March 16, 2017, 10:03 p.m.
On Thu, Mar 16, 2017 at 04:02:00PM +0530, Aneesh Kumar K.V wrote:
> For low slice max addr should be less that 4G
                                        ^^^^ than

A more verbose explanation of the off-by-1 error that you are fixing
is needed here.  Tell us what goes wrong with the current code and why
your fix is the correct one.

> 
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>

For the code change:

Reviewed-by: Paul Mackerras <paulus@ozlabs.org>
Aneesh Kumar K.V March 17, 2017, 6:55 a.m.
Paul Mackerras <paulus@ozlabs.org> writes:

> On Thu, Mar 16, 2017 at 04:02:00PM +0530, Aneesh Kumar K.V wrote:
>> For low slice max addr should be less that 4G
>                                         ^^^^ than
>
> A more verbose explanation of the off-by-1 error that you are fixing
> is needed here.  Tell us what goes wrong with the current code and why
> your fix is the correct one.

How about

powerpc/mm/slice: when computing slice mask limit low slice max addr correctly

For low slice, max addr should be less that 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.


>
>> 
>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
>
> For the code change:
>
> Reviewed-by: Paul Mackerras <paulus@ozlabs.org>

Patch hide | download patch | download mbox

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)