[PATCH] mm: cma: fix CMA aligned offset calculation

[PATCH] mm: cma: fix CMA aligned offset calculation

[Danesh Petigara]

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@vger.kernel.org
Signed-off-by: Danesh Petigara <dpetigara@broadcom.com>
Reviewed-by: Gregory Fong <gregory.0xf0@gmail.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

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

Re: [PATCH] mm: cma: fix CMA aligned offset calculation

[Gregory Fong]

[removed stable from cc]

On Tue, Feb 24, 2015 at 11:55 AM, Danesh Petigara
<dpetigara@broadcom.com> wrote:
> 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;

It was noticed that this doesn't remove the now-unused 'alignment'
variable, so I think Danesh is planning to submit an updated patch.

Best regards,
Gregory

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

Re: [PATCH] mm: cma: fix CMA aligned offset calculation

[Michal Nazarewicz]

On Tue, Feb 24 2015, Danesh Petigara <dpetigara@broadcom.com> wrote:
> 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@vger.kernel.org
> Signed-off-by: Danesh Petigara <dpetigara@broadcom.com>
> Reviewed-by: Gregory Fong <gregory.0xf0@gmail.com>

Acked-by: Michal Nazarewicz <mina86@mina86.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.
> +	 */

It probably makes sense to move this comment outside of the function as
function documentation.

> +	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
>

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

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

Re: [PATCH] mm: cma: fix CMA aligned offset calculation

[Danesh Petigara]

On 2/24/2015 1:10 PM, Michal Nazarewicz wrote:
> On Tue, Feb 24 2015, Danesh Petigara <dpetigara@broadcom.com> wrote:
>> 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@vger.kernel.org
>> Signed-off-by: Danesh Petigara <dpetigara@broadcom.com>
>> Reviewed-by: Gregory Fong <gregory.0xf0@gmail.com>
> 
> Acked-by: Michal Nazarewicz <mina86@mina86.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.
>> +	 */
> 
> It probably makes sense to move this comment outside of the function as
> function documentation.
> 

Thanks for the feedback. Will send out patch v2 with the comment moved
outside the function and also remove the unused 'alignment' variable.

>> +	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
>>
> 

Best regards,
Danesh Petigara

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>