linux-kernel - [PATCH] mm/cma: fix cma bitmap aligned mask computing

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Message-id: <000301cfe430$504b0290$f0e107b0$%yang@samsung.com>
Date:	Fri, 10 Oct 2014 10:15:53 +0800
From:	Weijie Yang <weijie.yang@...sung.com>
To:	iamjoonsoo.kim@....com
Cc:	mina86@...a86.com, aneesh.kumar@...ux.vnet.ibm.com,
	m.szyprowski@...sung.com,
	'Andrew Morton' <akpm@...ux-foundation.org>,
	'linux-kernel' <linux-kernel@...r.kernel.org>,
	'Linux-MM' <linux-mm@...ck.org>
Subject: [PATCH] mm/cma: fix cma bitmap aligned mask computing

The current cma bitmap aligned mask compute way is incorrect, it could
cause an unexpected align when using cma_alloc() if wanted align order
is bigger 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 input 15 as
expected align value, after using current computing, however, we get 0 as
cma bitmap aligned mask other than 511.

This patch fixes the cma bitmap aligned mask compute way.

Signed-off-by: Weijie Yang <weijie.yang@...sung.com>
---
 mm/cma.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/cma.c b/mm/cma.c
index c17751c..f6207ef 100644
--- a/mm/cma.c
+++ b/mm/cma.c
@@ -57,7 +57,10 @@ unsigned long cma_get_size(struct cma *cma)
 
 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;
+	else
+		return (1UL << (align_order - cma->order_per_bit)) - 1;
 }
 
 static unsigned long cma_bitmap_maxno(struct cma *cma)
-- 
1.7.10.4


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