[PATCH hmm 8/8] mm/hmm: add missing call to hmm_pte_need_fault in HMM_PFN_SPECIAL handling

[Christoph Hellwig]

On Wed, Mar 11, 2020 at 03:35:06PM -0300, Jason Gunthorpe wrote:
> From: Jason Gunthorpe <jgg at mellanox.com>
> 
> Currently if a special PTE is encountered hmm_range_fault() immediately
> returns EFAULT and sets the HMM_PFN_SPECIAL error output (which nothing
> uses).
> 
> EFAULT should only be returned after testing with hmm_pte_need_fault().
> 
> Also pte_devmap() and pte_special() are exclusive, and there is no need to
> check IS_ENABLED, pte_special() is stubbed out to return false on
> unsupported architectures.

I think the right fix is to just kill HMM_PFN_SPECIAL and treat any
fault on special ptes that aren't the zero page as an error.