V4L - Fix videobuf_dma_contig_user_get() getting page aligned physical address

  From: Muralidharan Karicheri <m-karicheri2@ti.com>

If a USERPTR address that is not aligned to page boundary is passed to the
videobuf_dma_contig_user_get() function, it saves a page aligned address to
the dma_handle. This is not correct. This issue is observed when using USERPTR
IO machism for buffer exchange.

Signed-off-by: Muralidharan Karicheri <m-karicheri2@ti.com>
---
Applies to V4L-DVB linux-next branch
 drivers/media/video/videobuf-dma-contig.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
  

On Wed, Dec 2, 2009 at 12:30 AM,  <m-karicheri2@ti.com> wrote:
> From: Muralidharan Karicheri <m-karicheri2@ti.com>
>
> If a USERPTR address that is not aligned to page boundary is passed to the
> videobuf_dma_contig_user_get() function, it saves a page aligned address to
> the dma_handle. This is not correct. This issue is observed when using USERPTR
> IO machism for buffer exchange.
>
> Signed-off-by: Muralidharan Karicheri <m-karicheri2@ti.com>

Thanks for the patch. For non-page aligned user space pointers I agree
that a fix is needed. Don't you think the while loop in
videobuf_dma_contig_user_get() also needs to be adjusted to include
the last page? I think the while loop checks one page too little in
the non-aligned case today.

Cheers,

/ magnus
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Magnus,

>Thanks for the patch. For non-page aligned user space pointers I agree
>that a fix is needed. Don't you think the while loop in
>videobuf_dma_contig_user_get() also needs to be adjusted to include
>the last page? I think the while loop checks one page too little in
>the non-aligned case today.
>
>Cheers,
>
>/ magnus

Thanks for reviewing my patch. It had worked for non-aligned address in
my testing. If I understand this code correctly, the physical address of
the user page start is determined in the first loop (pages_done == 0)
and additional loops are run to make sure the memory is physically
contiguous. Initially the mem->size is set to number of pages aligned to
page size. 

Assume we pass 4097 bytes as size.

mem->size = PAGE_ALIGN(vb->size); => 2

Inside the loop, iteration is done for 0 to pages-1.

pages_done < (mem->size >> 12) => pages_done < 2 => iterate 2 times

For size of 4096, we iterate once.
For size of 4095, we iterate once.

So IMO the loop is already iterate one more time when we pass non-aligned address since size is aligned to include the last page. So based on this
could you ack my patch so that we could ask Mauro to merge it with priority?

Murali Karicheri
Software Design Engineer
Texas Instruments Inc.
Germantown, MD 20874
phone: 301-407-9583
email: m-karicheri2@ti.com
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Hi again Murali,

Thanks for your work on this.

On Thu, Dec 3, 2009 at 12:48 AM, Karicheri, Muralidharan
<m-karicheri2@ti.com> wrote:
> Magnus,
>
>>Thanks for the patch. For non-page aligned user space pointers I agree
>>that a fix is needed. Don't you think the while loop in
>>videobuf_dma_contig_user_get() also needs to be adjusted to include
>>the last page? I think the while loop checks one page too little in
>>the non-aligned case today.
>
> Thanks for reviewing my patch. It had worked for non-aligned address in
> my testing. If I understand this code correctly, the physical address of
> the user page start is determined in the first loop (pages_done == 0)
> and additional loops are run to make sure the memory is physically
> contiguous. Initially the mem->size is set to number of pages aligned to
> page size.
>
> Assume we pass 4097 bytes as size.
>
> mem->size = PAGE_ALIGN(vb->size); => 2
>
> Inside the loop, iteration is done for 0 to pages-1.
>
> pages_done < (mem->size >> 12) => pages_done < 2 => iterate 2 times
>
> For size of 4096, we iterate once.
> For size of 4095, we iterate once.
>
> So IMO the loop is already iterate one more time when we pass non-aligned address since size is aligned to include the last page. So based on this
> could you ack my patch so that we could ask Mauro to merge it with priority?

I think your observations are correct, but I also think there is one
more hidden issue. In the case where the offset within the page is
other than 0 then we should loop once more to also check the final
page. Right now no one is checking if the last page is contiguous or
not in the case on non-page-aligned offset..

So in your case with a 4096 or 4095 size, but if the offset withing
the page is non-zero then we should loop twice to make sure the pages
really are physically contiguous. Today we only loop once based on the
size. We should also include the offset in the calculation of number
of pages to check.

If you can include that fix in your patch that would be great. If not
then i'll fix it up myself.

Thanks!

/ magnus
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Murali Karicheri
Software Design Engineer
Texas Instruments Inc.
Germantown, MD 20874
phone: 301-407-9583
email: m-karicheri2@ti.com

>-----Original Message-----
>From: Magnus Damm [mailto:magnus.damm@gmail.com]
>Sent: Friday, December 04, 2009 6:06 AM
>To: Karicheri, Muralidharan
>Cc: linux-media@vger.kernel.org; mchehab@infradead.org; davinci-linux-open-
>source@linux.davincidsp.com
>Subject: Re: [PATCH] V4L - Fix videobuf_dma_contig_user_get() getting page
>aligned physical address
>
>Hi again Murali,
>
>Thanks for your work on this.
>
>On Thu, Dec 3, 2009 at 12:48 AM, Karicheri, Muralidharan
><m-karicheri2@ti.com> wrote:
>> Magnus,
>>
>>>Thanks for the patch. For non-page aligned user space pointers I agree
>>>that a fix is needed. Don't you think the while loop in
>>>videobuf_dma_contig_user_get() also needs to be adjusted to include
>>>the last page? I think the while loop checks one page too little in
>>>the non-aligned case today.
>>
>> Thanks for reviewing my patch. It had worked for non-aligned address in
>> my testing. If I understand this code correctly, the physical address of
>> the user page start is determined in the first loop (pages_done == 0)
>> and additional loops are run to make sure the memory is physically
>> contiguous. Initially the mem->size is set to number of pages aligned to
>> page size.
>>
>> Assume we pass 4097 bytes as size.
>>
>> mem->size = PAGE_ALIGN(vb->size); => 2
>>
>> Inside the loop, iteration is done for 0 to pages-1.
>>
>> pages_done < (mem->size >> 12) => pages_done < 2 => iterate 2 times
>>
>> For size of 4096, we iterate once.
>> For size of 4095, we iterate once.
>>
>> So IMO the loop is already iterate one more time when we pass non-aligned
>address since size is aligned to include the last page. So based on this
>> could you ack my patch so that we could ask Mauro to merge it with
>priority?
>
>I think your observations are correct, but I also think there is one
>more hidden issue. In the case where the offset within the page is
>other than 0 then we should loop once more to also check the final
>page. Right now no one is checking if the last page is contiguous or
>not in the case on non-page-aligned offset..
>
>So in your case with a 4096 or 4095 size, but if the offset withing
>the page is non-zero then we should loop twice to make sure the pages
>really are physically contiguous. Today we only loop once based on the
>size. We should also include the offset in the calculation of number
>of pages to check.

Yes. You are right. For offsets that are non-aligned we need to check 
for the last one.

Probably

unsigned int offset = vb->baddr & ~PAGE_MASK;
mem->size = PAGE_ALIGN(vb->size + offset); 


......

if (pages_done == 0)
	mem->handle = (this_pfn << PAGE_SHIFT) + offset;

If this is fine, I can send you a updated patch. If you can fix it that is fine too.

regards,

Murali
>
>If you can include that fix in your patch that would be great. If not
>then i'll fix it up myself.
>

If you could do this it will be great!

>Thanks!
>
>/ magnus
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