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

Dan Williams
2019-11-13T01:35:59Z

On Tue, Nov 12, 2019 at 5:08 PM John Hubbard <jhubbard@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?