[PATCH 3.17 108/146] mm/cma: fix cma bitmap aligned mask computing

[Greg Kroah-Hartman]

3.17-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Weijie Yang <weijie.yang@xxxxxxxxxxx>

commit 68faed630fc151a7a1c4853df00fb3dcacf782b4 upstream.

The current cma bitmap aligned mask computation is incorrect.  It could
cause an unexpected alignment when using cma_alloc() if the wanted align
order is larger than cma->order_per_bit.

Take kvm for example (PAGE_SHIFT = 12), kvm_cma->order_per_bit is set to
6.  When kvm_alloc_rma() tries to alloc kvm_rma_pages, it will use 15 as
the expected align value.  After using the current implementation however,
we get 0 as cma bitmap aligned mask other than 511.

This patch fixes the cma bitmap aligned mask calculation.

[akpm@xxxxxxxxxxxxxxxxxxxx: coding-style fixes]
Signed-off-by: Weijie Yang <weijie.yang@xxxxxxxxxxx>
Acked-by: Michal Nazarewicz <mina86@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 mm/cma.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/mm/cma.c
+++ b/mm/cma.c
@@ -57,7 +57,9 @@ unsigned long cma_get_size(struct cma *c
 
 static unsigned long cma_bitmap_aligned_mask(struct cma *cma, int align_order)
 {
-	return (1UL << (align_order >> cma->order_per_bit)) - 1;
+	if (align_order <= cma->order_per_bit)
+		return 0;
+	return (1UL << (align_order - cma->order_per_bit)) - 1;
 }
 
 static unsigned long cma_bitmap_maxno(struct cma *cma)


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