[patch 13/28] mm: fail get_vaddr_frames() for filesystem-dax mappings

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From: Dan Williams <dan.j.williams@xxxxxxxxx>
Subject: 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@xxxxxxxxx: add comment for vma_is_fsdax() check in get_vaddr_frames(), per Jan]
  Link: http://lkml.kernel.org/r/151197874035.26211.4061781453123083667.stgit@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/151068939985.7446.15684639617389154187.stgit@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 3565fce3a659 ("mm, x86: get_user_pages() for dax mappings")
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Reviewed-by: Jan Kara <jack@xxxxxxx>
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: Mel Gorman <mgorman@xxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Doug Ledford <dledford@xxxxxxxxxx>
Cc: Hal Rosenstock <hal.rosenstock@xxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxxxxxx>
Cc: Jeff Moyer <jmoyer@xxxxxxxxxx>
Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Cc: Sean Hefty <sean.hefty@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 mm/frame_vector.c |   12 ++++++++++++
 1 file changed, 12 insertions(+)

diff -puN mm/frame_vector.c~mm-fail-get_vaddr_frames-for-filesystem-dax-mappings mm/frame_vector.c
--- a/mm/frame_vector.c~mm-fail-get_vaddr_frames-for-filesystem-dax-mappings
+++ a/mm/frame_vector.c
@@ -53,6 +53,18 @@ int get_vaddr_frames(unsigned long start
 		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;
_
--
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