On Tue 14-11-17 11:56:39, Dan Williams wrote:
> Until there is a solution to the dma-to-dax vs truncate problem it is
> not safe to allow V4L2, Exynos, and other frame vector users to create
> long standing / irrevocable memory registrations against filesytem-dax
> vmas.
>
> Cc: Inki Dae <inki.dae@xxxxxxxxxxx>
> Cc: Seung-Woo Kim <sw0312.kim@xxxxxxxxxxx>
> Cc: Joonyoung Shim <jy0922.shim@xxxxxxxxxxx>
> Cc: Kyungmin Park <kyungmin.park@xxxxxxxxxxx>
> Cc: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx>
> Cc: linux-media@xxxxxxxxxxxxxxx
> Cc: Jan Kara <jack@xxxxxxx>
> Cc: Mel Gorman <mgorman@xxxxxxx>
> Cc: Vlastimil Babka <vbabka@xxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx>
> Fixes: 3565fce3a659 ("mm, x86: get_user_pages() for dax mappings")
> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Makes sense. I'd just note that in principle get_vaddr_frames() is no more
long-term than get_user_pages(). It is just so that all the users of
get_vaddr_frames() currently want a long-term reference. Maybe could you
add here also a comment that the vma_is_fsdax() check is there because all
users of this function want a long term page reference? With that you can
add:
Reviewed-by: Jan Kara <jack@xxxxxxx>
Honza
> ---
> mm/frame_vector.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/mm/frame_vector.c b/mm/frame_vector.c
> index 72ebec18629c..d2fdbeaadc8b 100644
> --- a/mm/frame_vector.c
> +++ b/mm/frame_vector.c
> @@ -52,6 +52,10 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames,
> ret = -EFAULT;
> goto out;
> }
> +
> + if (vma_is_fsdax(vma))
> + return -EOPNOTSUPP;
> +
> if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) {
> vec->got_ref = true;
> vec->is_pfns = false;
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
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