Re: [PATCH v3 08/23] vfio, mm: fix get_user_pages_remote() and FOLL_LONGTERM

On Tue, Nov 12, 2019 at 2:43 PM John Hubbard jhubbard@nvidia.com wrote:

On 11/12/19 12:43 PM, Jason Gunthorpe wrote: ...

...

...

•        }
  

• ret = get_user_pages_remote(NULL, mm, vaddr, 1, flags | FOLL_LONGTERM,

•                            page, vmas, NULL);
  

• /*

• * The lifetime of a vaddr_get_pfn() page pin is
  

• * userspace-controlled. In the fs-dax case this could
  

• * lead to indefinite stalls in filesystem operations.
  

• * Disallow attempts to pin fs-dax pages via this
  

• * interface.
  

• */
  

• if (ret > 0 && vma_is_fsdax(vmas[0])) {

•        ret = -EOPNOTSUPP;
  

•        put_page(page[0]);
  

  }

AFAIK this chunk is redundant now as it is some hack to emulate FOLL_LONGTERM? So vmas can be deleted too.

Let me first make sure I understand what Dan has in mind for the vma checking, in the other thread...

It's not redundant relative to upstream which does not do anything the FOLL_LONGTERM in the gup-slow path... but I have not looked at patches 1-7 to see if something there made it redundant.