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

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

[Weijie Yang]

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@samsung.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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Re: [PATCH] mm/cma: fix cma bitmap aligned mask computing

[Michal Nazarewicz]

On Fri, Oct 10 2014, Weijie Yang wrote:
> 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@samsung.com>

Acked-by: Michal Nazarewicz <mina86@mina86.com>

Should that also get:

Cc: <stable@vger.kernel.org> # v3.17

> ---
>  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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.o. | Liege of Serenely Enlightened Majesty of      o' \,=./ `o
..o | Computer Science,  Michał “mina86” Nazarewicz    (o o)
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