[Nouveau] 4.9-rc7 nouveau fails on arm64 64k page kernel but works with 4k

[Ilia Mirkin]

On Wed, Dec 7, 2016 at 4:57 AM, Alexandre Courbot <gnurou at gmail.com> wrote:
> On Wed, Dec 7, 2016 at 6:53 PM, Michel Dänzer <michel at daenzer.net> wrote:
>> On 07/12/16 06:39 PM, Alexandre Courbot wrote:
>>> On Fri, Dec 2, 2016 at 12:23 PM, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
>>>> That's right -- nouveau currently requires 4k page sizes to work. This is a
>>>> software limitation, not a hardware one though.
>>>
>>> Looking at the trace I wonder - is the limitation in Nouveau or in TTM?
>>
>> Nouveau. Non-4K page sizes work fine with radeon (and presumably amdgpu).
>
> Thanks for the precision. I will check if Tegra iGPUs are also
> affected by this - if they are then it gives me a good excuse to take
> care of this bug.

For the most part it's confusion in the (nouveau) code as to what's a
gpu page and what's a cpu page (and the shifts involved). There are
some fringe issues that will need to be addressed, like the fact that
it's no longer a 1:1 mapping, which might be assumed in some places.

However I thought that 64K-pages were frowned upon nowadays for the
kernel - outside of HPC loads, most of the kernel memory becomes
pagecache, and files don't tend to be 64K-sized, so you have tons of
wasted memory (since you never cache multiple files in the same page).

But don't take that as me disapproving of such a project. It'd esp be
nice to do something like this outside of the PPC64 environment, where
BE concerns mix in with the 64K page concerns, and nothing works as a
result.

  -ilia