Re: [PATCH] mm: Export symbols unmapped_area() & unmapped_area_topdown()

[Olu Ogunbowale]

On Thu, Mar 17, 2016 at 06:03:50PM +0100, Jerome Glisse wrote:
> Well trick still works, if driver is loaded early during userspace program
> initialization then you force mmap to specific range inside the driver
> userspace code. If driver is loaded after and program is already using those
> range then you can register a notifier to track when those range. If they
> get release by the program you can have the userspace driver force creation
> of new reserve vma again.

I should have been more clearer in my response, this applies only because
we are in a scheme were all allocations must go through a special allocator 
because VMA base/range is reserved for SVM.

> Well controling range into which VMA can be allocated is not something that
> you should do lightly (thing like address space randomization would be
> impacted). And no the SVM range is not upper bound by the amount of memory
> but by the physical bus size if it is 48bits nothing forbid to put all the
> program memory above 8GB and nothing below. We are talking virtual address
> here. By the way i think most 64 bit ARM are 40 bits and it seems a shame
> for GPU to not go as high as the CPU.

Same as above. By the way, we support minimum 40-bits but can be paired with
CPU(s) of higher bits; no problem if bits are equal or greater than CPU.