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

[Jason Gunthorpe]

On Mon, Mar 16, 2020 at 10:13:47AM +0100, Christoph Hellwig wrote:
> 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.
 
I have another series that is doing that - this change is to make the
next series make sense and not introduce new control logic too.

Even when this is switched to ERROR it still needs to have the
hmm_range_fault() logic this patch introduces.

Thanks,
Jason