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

[Dan Williams]

On Tue, Nov 12, 2019 at 5:08 PM John Hubbard <jhubbard at nvidia.com> wrote:
>
> On 11/12/19 4:58 PM, Dan Williams wrote:
> ...
> >>> 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.
> >>
> >> Oh, the hunk John had below for get_user_pages_remote() also needs to
> >> call __gup_longterm_locked() when FOLL_LONGTERM is specified, then
> >> that calls check_dax_vmas() which duplicates the vma_is_fsdax() check
> >> above.
> >
> > Oh true, good eye. It is redundant if it does additionally call
> > __gup_longterm_locked(), and it needs to do that otherwises it undoes
> > the CMA migration magic that Aneesh added.
> >
>
> OK. So just to be clear, I'll be removing this from the patch:
>
>         /*
>          * 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]);
>         }
>
> (and the declaration of "vmas", as well).

...and add a call to __gup_longterm_locked internal to
get_user_pages_remote(), right?