linux-kernel - [PATCH v3 2/4] mm: fail get_vaddr_frames() for filesystem-dax mappings

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Message-ID: <151197874035.26211.4061781453123083667.stgit@dwillia2-desk3.amr.corp.intel.com>
Date:   Wed, 29 Nov 2017 10:05:40 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     akpm@...ux-foundation.org
Cc:     Jan Kara <jack@...e.cz>, Joonyoung Shim <jy0922.shim@...sung.com>,
        linux-nvdimm@...ts.01.org, Seung-Woo Kim <sw0312.kim@...sung.com>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Inki Dae <inki.dae@...sung.com>, linux-mm@...ck.org,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Mel Gorman <mgorman@...e.de>,
        Mauro Carvalho Chehab <mchehab@...nel.org>, hch@....de,
        Vlastimil Babka <vbabka@...e.cz>, linux-media@...r.kernel.org
Subject: [PATCH v3 2/4] 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.

Cc: Inki Dae <inki.dae@...sung.com>
Cc: Seung-Woo Kim <sw0312.kim@...sung.com>
Cc: Joonyoung Shim <jy0922.shim@...sung.com>
Cc: Kyungmin Park <kyungmin.park@...sung.com>
Cc: Mauro Carvalho Chehab <mchehab@...nel.org>
Cc: linux-media@...r.kernel.org
Cc: Mel Gorman <mgorman@...e.de>
Cc: Vlastimil Babka <vbabka@...e.cz>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: <stable@...r.kernel.org>
Fixes: 3565fce3a659 ("mm, x86: get_user_pages() for dax mappings")
Reviewed-by: Jan Kara <jack@...e.cz>
Signed-off-by: Dan Williams <dan.j.williams@...el.com>
---
 mm/frame_vector.c |   12 ++++++++++++
 1 file changed, 12 insertions(+)

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;