Re: [PATCH 04/15] mm: remove the pgmap field from struct hmm_vma_walk

[Christoph Hellwig]

On Fri, Aug 16, 2019 at 12:43:07AM +0000, Jason Gunthorpe wrote:
> On Thu, Aug 15, 2019 at 04:51:33PM -0400, Jerome Glisse wrote:
> 
> > struct page. In this case any way we can update the
> > nouveau_dmem_page() to check that page page->pgmap == the
> > expected pgmap.
> 
> I was also wondering if that is a problem.. just blindly doing a
> container_of on the page->pgmap does seem like it assumes that only
> this driver is using DEVICE_PRIVATE.
> 
> It seems like something missing in hmm_range_fault, it should be told
> what DEVICE_PRIVATE is acceptable to trigger HMM_PFN_DEVICE_PRIVATE
> and fault all others?

The whole device private handling in hmm and migrate_vma seems pretty
broken as far as I can tell, and I have some WIP patches.  Basically we
should not touch (or possibly eventually call migrate to ram eventually
in the future) device private pages not owned by the caller, where I
try to defined the caller by the dev_pagemap_ops instance.