Subject: Re: [PATCH] ion: scatterlist offset not used for buffer map
To: gregkh@linuxfoundation.org, arve@android.com, devel@driverdev.osuosl.org,
        linux-kernel@vger.kernel.org
References: <1460028599-22356-1-git-send-email-john.reitan@foss.arm.com>
 <5706B70E.4040004@redhat.com>
 <20160408065626.GA25580@e106921-lin.trondheim.arm.com>
From: Laura Abbott <labbott@redhat.com>
Message-ID: <5708342F.8070704@redhat.com>
Date: Fri, 8 Apr 2016 15:43:59 -0700
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On 04/07/2016 11:56 PM, John Einar Reitan wrote:
> On Thu, Apr 07, 2016 at 12:37:50PM -0700, Laura Abbott wrote:
>> On 04/07/2016 04:29 AM, John Einar Reitan wrote:
>>> ion's default user/kernel page mapping code don't honor the offset
>>> option for scatterlists. It uses sg_page and expect the whole page to be
>>> mapped, while the offset could dictate an offset within a large page.
>>>
>>> sg_phys correctly accounts for the offset, so should be used instead.
>>>
>>
>> Can you be more specific about which heap and which allocation pattern
>> is exposing this bug?
>
> The heap that exposed the bug is one I'm developing and will be posting
> as a RFC soon. It uses compound pages and an sub-divides it into surface
> buffers. The ion buffers are configured to hold sgl's with the compound
> page and the correct offset of the buffer, via
> sg_set_page(.., compound_page, .., offset_of_logical_buffer);
>
> sg_phys/sg_virt  includes this offset, but if you poke the sg and extract
> the page with sg_page yourself you must include this offset in your
> calculations too.
>

This patch should be re-sent when you have the RFC for the heap. Unless
there is a heap available in tree we don't really need this patch.

Thanks,
Laura