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

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Date:	Fri, 10 Oct 2014 16:18:54 +0200
From:	Michal Nazarewicz <mina86@...a86.com>
To:	Weijie Yang <weijie.yang@...sung.com>, iamjoonsoo.kim@....com
Cc:	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: Re: [PATCH] mm/cma: fix cma bitmap aligned mask computing

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@...sung.com>

Acked-by: Michal Nazarewicz <mina86@...a86.com>

Should that also get:

Cc: <stable@...r.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
>
>

-- 
Best regards,                                         _     _
.o. | Liege of Serenely Enlightened Majesty of      o' \,=./ `o
..o | Computer Science,  Michał “mina86” Nazarewicz    (o o)
ooo +--<mpn@...gle.com>--<xmpp:mina86@...ber.org>--ooO--(_)--Ooo--
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