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

Christoph Hellwig
2019-08-08T07:53:58Z

On Wed, Aug 07, 2019 at 01:38:08PM +0100, Mark Rutland wrote:
> > I *believe* that there are not alias mappings (that I don't control
> > myself) for pages coming from
> > shmem_file_setup()/shmem_read_mapping_page()..
>
> AFAICT, that's regular anonymous memory, so there will be a cacheable
> alias in the linear/direct map.

Yes. Although shmem is in no way special in that regard. Even with the
normal dma_alloc_coherent implementation on arm and arm64 we keep the
cacheable alias in the direct mapping and just create a new non-cacheable
one. The only exception are CMA allocations on 32-bit arm, which do
get remapped to uncachable in place.