From 4c806b897d6075bfa5067e524fb058c57ab64e7b Mon Sep 17 00:00:00 2001
From: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Date: Tue, 24 Sep 2019 17:13:27 +0530
Subject: [PATCH] libnvdimm/region: Enable MAP_SYNC for volatile regions
Git-commit: 4c806b897d6075bfa5067e524fb058c57ab64e7b
Patch-mainline: v5.4-rc1
References: bsc#1161291

Some environments want to use a host tmpfs/ramdisk to back guest pmem.
While the data is not persisted relative to the host it *is* persisted
relative to guest crashes / reboots. The guest is free to use dax and
MAP_SYNC to keep filesystem metadata consistent with dax accesses
without requiring guest fsync(). The guest can also observe that the
region is volatile and skip cache flushing as global visibility is
enough to "persist" data relative to the host staying alive over guest
reset events.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Reviewed-by: Pankaj Gupta <pagupta@redhat.com>
Link: https://lore.kernel.org/r/20190924114327.14700-1-aneesh.kumar@linux.ibm.com
[djbw: reword the changelog]
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Acked-by: Jan Kara <jack@suse.cz>

---
 drivers/nvdimm/region_devs.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/nvdimm/region_devs.c b/drivers/nvdimm/region_devs.c
index ab91890f2486..ef423ba1a711 100644
--- a/drivers/nvdimm/region_devs.c
+++ b/drivers/nvdimm/region_devs.c
@@ -1168,6 +1168,9 @@ EXPORT_SYMBOL_GPL(nvdimm_has_cache);
 
 bool is_nvdimm_sync(struct nd_region *nd_region)
 {
+	if (is_nd_volatile(&nd_region->dev))
+		return true;
+
 	return is_nd_pmem(&nd_region->dev) &&
 		!test_bit(ND_REGION_ASYNC, &nd_region->flags);
 }
-- 
2.16.4