On Thu, May 30, 2019 at 06:54:04AM +0800, Pingfan Liu wrote:
> As for FOLL_LONGTERM, it is checked in the slow path
> __gup_longterm_unlocked(). But it is not checked in the fast path, which
> means a possible leak of CMA page to longterm pinned requirement through
> this crack.
>
> Place a check in the fast path.
>
> Signed-off-by: Pingfan Liu <kernelfans@xxxxxxxxx>
> Cc: Ira Weiny <ira.weiny@xxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Mike Rapoport <rppt@xxxxxxxxxxxxx>
> Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> Cc: John Hubbard <jhubbard@xxxxxxxxxx>
> Cc: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxx>
> Cc: Keith Busch <keith.busch@xxxxxxxxx>
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> ---
> mm/gup.c | 12 ++++++++++++
> 1 file changed, 12 insertions(+)
>
> diff --git a/mm/gup.c b/mm/gup.c
> index f173fcb..00feab3 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -2235,6 +2235,18 @@ int get_user_pages_fast(unsigned long start, int nr_pages,
> local_irq_enable();
> ret = nr;
> }
> +#if defined(CONFIG_CMA)
> + if (unlikely(gup_flags & FOLL_LONGTERM)) {
> + int i, j;
> +
> + for (i = 0; i < nr; i++)
> + if (is_migrate_cma_page(pages[i])) {
> + for (j = i; j < nr; j++)
> + put_page(pages[j]);
Should be put_user_page() now. For now that just calls put_page() but it is
slated to change soon.
I also wonder if this would be more efficient as a check as we are walking the
page tables and bail early.
Perhaps the code complexity is not worth it?
> + nr = i;
Why not just break from the loop here?
Or better yet just use 'i' in the inner loop...
Ira
> + }
> + }
> +#endif
>
> if (nr < nr_pages) {
> /* Try to get the remaining pages with get_user_pages */
> --
> 2.7.5
>
