Re: [PATCH 1/2] drm: add cache support for arm64

[Christoph Hellwig]

On Wed, Aug 07, 2019 at 10:30:04AM -0700, Rob Clark wrote:
> So, we do end up using GFP_HIGHUSER, which appears to get passed thru
> when shmem gets to the point of actually allocating pages.. not sure
> if that just ends up being a hint, or if it guarantees that we don't
> get something in the linear map.
> 
> (Bear with me while I "page" this all back in.. last time I dug thru
> the shmem code was probably pre-armv8, or at least before I had any
> armv8 hw)

GFP_HIGHUSER basically just means that this is an allocation that could
dip into highmem, in which case it would not have a kernel mapping.
This can happen on arm + LPAE, but not on arm64.