[PATCH] exynos: Put a stop to the userptr heresy.

[Inki Dae]

On 2014년 07월 09일 18:23, Daniel Vetter wrote:
> On Tue, Jul 8, 2014 at 6:20 PM, Inki Dae <inki.dae at samsung.com> wrote:
>> 2014-07-08 22:37 GMT+09:00 Daniel Vetter <daniel at ffwll.ch>:
>>> On Wed, Jul 02, 2014 at 11:25:19AM -0400, Jerome Glisse wrote:
>>>> Anyway as this is upstream i guess you can keep it. This is just an horrible
>>>> API that allow to circumvant any limit set by memcg for page locking and all.
>>>> But anyway GPU driver never played in the same ballpark as other driver.
>>>
>>> I agree that exynos userptr as-is should be removed since as opposed to
>>> the i915 implementation it doesn't play nice with the core mm
>>
>> Can you give me more details why you think so?
> 
>>From a very quick look there's two pieces:
> - The implementation with the vma tricks looks _really_ scary. You'd
> need to have Al Viro's opinion on it though.

You mean that it checks VM_DONTCOPY flag before copying vma? If so, I
really forgot it.

> - If I'm reading the code correctly userspace can pin unlimted amounts
> of memory, but I've gotten a bit lost in the code. In i915 we have

Not so. g2d driver is checking if user-requested buffer size is more
than maximum capacity of g2d dma. So it can never pin unlimited amounts
of memory.

> shrinkers and mmu notifier to make sure that if the vm needs this
> memory again we'll make it available.

I am not familiar to mmu notifier. I will look into how i915 driver
handle it.

Thanks for comments,
Inki Dae

> -Daniel
>