mm: fail get_vaddr_frames() for filesystem-dax mappings

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.

[dan.j.williams@intel.com: add comment for vma_is_fsdax() check in get_vaddr_frames(), per Jan]
  Link: http://lkml.kernel.org/r/151197874035.26211.4061781453123083667.stgit@dwillia2-desk3.amr.corp.intel.com
Link: http://lkml.kernel.org/r/151068939985.7446.15684639617389154187.stgit@dwillia2-desk3.amr.corp.intel.com
Fixes: 3565fce3a659 ("mm, x86: get_user_pages() for dax mappings")
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Inki Dae <inki.dae@samsung.com>
Cc: Seung-Woo Kim <sw0312.kim@samsung.com>
Cc: Joonyoung Shim <jy0922.shim@samsung.com>
Cc: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Doug Ledford <dledford@redhat.com>
Cc: Hal Rosenstock <hal.rosenstock@gmail.com>
Cc: Jason Gunthorpe <jgg@mellanox.com>
Cc: Jeff Moyer <jmoyer@redhat.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Sean Hefty <sean.hefty@intel.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 12 insertions, 0 deletions

diff --git a/mm/frame_vector.c b/mm/frame_vector.c
index 2f98df0d460e..297c7238f7d4 100644
--- a/mm/frame_vector.c
+++ b/mm/frame_vector.c
@@ -53,6 +53,18 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames,
                 ret = -EFAULT;
                 goto out;
         }
+
+        /*
+         * While get_vaddr_frames() could be used for transient (kernel
+         * controlled lifetime) pinning of memory pages all current
+         * users establish long term (userspace controlled lifetime)
+         * page pinning. Treat get_vaddr_frames() like
+         * get_user_pages_longterm() and disallow it for filesystem-dax
+         * mappings.
+         */
+        if (vma_is_fsdax(vma))
+                return -EOPNOTSUPP;
+
         if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) {
                 vec->got_ref = true;
                 vec->is_pfns = false;