[PATCH V2] arm64: optimized copy_to_user and copy_from_user assembly code

[Dann Frazier]

On Thu, Dec 4, 2014 at 6:56 AM, Dr. Philipp Tomsich
<philipp.tomsich at theobroma-systems.com> wrote:
> Craig/Steve/Dann,
>
> trying to understand what went wrong and when, I just went back to my original mail (May 1st, 2013) providing the original optimized functions for an iperf run at APM… this had two separate error-handling paths for _to_user and _from_user, where the _to_user case didn’t zeroize.
>
> I can’t quite track when these two paths were unified (or by who)… but I can confirm that only the _from_user path was designed to zeroize the buffer on error.

This is the source we pulled (previous version had some issues w/
licensing iirc):
  http://www.spinics.net/lists/arm-kernel/msg353650.html

 -dann

> @Craig: I’ll also forward you the original files, which I had earlier sent to Dann on Jul 3rd 2014. This should provide a point-of-reference for resolving this.
>
> Best,
> Philipp.
>
>> On 04 Dec 2014, at 13:27, Steve Capper <steve.capper at linaro.org> wrote:
>>
>> On 3 December 2014 at 20:01, Craig Magina <craig.magina at canonical.com> wrote:
>> [...]
>>>
>>> Could you provide the steps you used to reproduce this issue? I have
>>> already submitted an SRU to revert this patch, but would like to have
>>> the method you used to reproduce it for testing. Thanks for reporting
>>> this.
>>>
>>> --
>>> Craig Magina
>>
>> Hi Craig,
>> It's not easy to reproduce as the problem occurs when the kernel is
>> copying memory to userspace and experiences a page fault.
>>
>> I have come across it whilst running "perf record -a" on a system that
>> is swapping.
>>
>> Also, building source code under memory pressure (i.e. kernel compile
>> just after the system has swapped out pages), gave me this problem
>> too.
>>
>> Cheers,
>> --
>> Steve
>