[PATCH 2/2] mm: cma: Align to physical address, not CMA region position

[Gregory Fong]

The alignment in cma_alloc() was done w.r.t. the bitmap.  This is a
problem when, for example:

- a device requires 16M (order 12) alignment
- the CMA region is not 16 M aligned

In such a case, can result with the CMA region starting at, say,
0x2f800000 but any allocation you make from there will be aligned from
there.  Requesting an allocation of 32 M with 16 M alignment will
result in an allocation from 0x2f800000 to 0x31800000, which doesn't
work very well if your strange device requires 16M alignment.

Change to use bitmap_find_next_zero_area_off() to account for the
difference in alignment at reserve-time and alloc-time.

Cc: Michal Nazarewicz <mina86 at mina86.com>
Signed-off-by: Gregory Fong <gregory.0xf0 at gmail.com>
---
 mm/cma.c | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/mm/cma.c b/mm/cma.c
index fde706e..0813599 100644
--- a/mm/cma.c
+++ b/mm/cma.c
@@ -63,6 +63,17 @@ static unsigned long cma_bitmap_aligned_mask(struct cma *cma, int align_order)
 	return (1UL << (align_order - cma->order_per_bit)) - 1;
 }
 
+static unsigned long cma_bitmap_aligned_offset(struct cma *cma, int align_order)
+{
+	unsigned int alignment;
+
+	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);
+}
+
 static unsigned long cma_bitmap_maxno(struct cma *cma)
 {
 	return cma->count >> cma->order_per_bit;
@@ -328,7 +339,7 @@ err:
  */
 struct page *cma_alloc(struct cma *cma, int count, unsigned int align)
 {
-	unsigned long mask, pfn, start = 0;
+	unsigned long mask, offset, pfn, start = 0;
 	unsigned long bitmap_maxno, bitmap_no, bitmap_count;
 	struct page *page = NULL;
 	int ret;
@@ -343,13 +354,15 @@ struct page *cma_alloc(struct cma *cma, int count, unsigned int align)
 		return NULL;
 
 	mask = cma_bitmap_aligned_mask(cma, align);
+	offset = cma_bitmap_aligned_offset(cma, align);
 	bitmap_maxno = cma_bitmap_maxno(cma);
 	bitmap_count = cma_bitmap_pages_to_bits(cma, count);
 
 	for (;;) {
 		mutex_lock(&cma->lock);
-		bitmap_no = bitmap_find_next_zero_area(cma->bitmap,
-				bitmap_maxno, start, bitmap_count, mask);
+		bitmap_no = bitmap_find_next_zero_area_off(cma->bitmap,
+				bitmap_maxno, start, bitmap_count, mask,
+				offset);
 		if (bitmap_no >= bitmap_maxno) {
 			mutex_unlock(&cma->lock);
 			break;
-- 
1.9.1