linux-kernel - [PATCH] mm: cma: fix CMA aligned offset calculation

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Date:	Tue, 24 Feb 2015 11:55:59 -0800
From:	Danesh Petigara <dpetigara@...adcom.com>
To:	<akpm@...ux-foundation.org>
CC:	<m.szyprowski@...sung.com>, <mina86@...a86.com>,
	<iamjoonsoo.kim@....com>, <aneesh.kumar@...ux.vnet.ibm.com>,
	<laurent.pinchart+renesas@...asonboard.com>,
	<gregory.0xf0@...il.com>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>,
	Danesh Petigara <dpetigara@...adcom.com>,
	<stable@...r.kernel.org>
Subject: [PATCH] mm: cma: fix CMA aligned offset calculation

The CMA aligned offset calculation is incorrect for
non-zero order_per_bit values.

For example, if cma->order_per_bit=1, cma->base_pfn=
0x2f800000 and align_order=12, the function returns
a value of 0x17c00 instead of 0x400.

This patch fixes the CMA aligned offset calculation.

Cc: stable@...r.kernel.org
Signed-off-by: Danesh Petigara <dpetigara@...adcom.com>
Reviewed-by: Gregory Fong <gregory.0xf0@...il.com>
---
 mm/cma.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/mm/cma.c b/mm/cma.c
index 75016fd..58f37bd 100644
--- a/mm/cma.c
+++ b/mm/cma.c
@@ -70,9 +70,13 @@ static unsigned long cma_bitmap_aligned_offset(struct cma *cma, int align_order)
 
 	if (align_order <= cma->order_per_bit)
 		return 0;
-	alignment = 1UL << (align_order - cma->order_per_bit);
-	return ALIGN(cma->base_pfn, alignment) -
-		(cma->base_pfn >> cma->order_per_bit);
+
+	/*
+	 * Find a PFN aligned to the specified order and return
+	 * an offset represented in order_per_bits.
+	 */
+	return (ALIGN(cma->base_pfn, (1UL << align_order))
+		- cma->base_pfn) >> cma->order_per_bit;
 }
 
 static unsigned long cma_bitmap_maxno(struct cma *cma)
-- 
1.9.1

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