From: Dan Williams <dan.j.williams@intel.com>
Date: Fri, 9 Jun 2017 09:46:50 -0700
Subject: libnvdimm, pmem: disable dax flushing when pmem is fronting a
 volatile region
Patch-mainline: v4.13-rc1
Git-commit: 0b277961f4484fb3f142caaa1dd1748cb0b2cbee
References: FATE#323717

The pmem driver attaches to both persistent and volatile memory ranges
advertised by the ACPI NFIT. When the region is volatile it is redundant
to spend cycles flushing caches at fsync(). Check if the hosting region
is volatile and do not set dax_write_cache() if it is.

Cc: Jan Kara <jack@suse.cz>
Cc: Jeff Moyer <jmoyer@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Matthew Wilcox <mawilcox@microsoft.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Acked-by: Johannes Thumshirn <jthumshirn@suse.de>
---
 drivers/nvdimm/pmem.c        |   13 ++++++++-----
 drivers/nvdimm/region_devs.c |    6 ++++++
 include/linux/libnvdimm.h    |    1 +
 3 files changed, 15 insertions(+), 5 deletions(-)

--- a/drivers/nvdimm/pmem.c
+++ b/drivers/nvdimm/pmem.c
@@ -285,10 +285,10 @@ static int pmem_attach_disk(struct devic
 	struct nd_namespace_io *nsio = to_nd_namespace_io(&ndns->dev);
 	struct nd_region *nd_region = to_nd_region(dev->parent);
 	struct vmem_altmap __altmap, *altmap = NULL;
+	int nid = dev_to_node(dev), fua, wbc;
 	struct resource *res = &nsio->res;
 	struct nd_pfn *nd_pfn = NULL;
 	struct dax_device *dax_dev;
-	int nid = dev_to_node(dev);
 	struct nd_pfn_sb *pfn_sb;
 	struct pmem_device *pmem;
 	struct resource pfn_res;
@@ -315,9 +315,12 @@ static int pmem_attach_disk(struct devic
 	dev_set_drvdata(dev, pmem);
 	pmem->phys_addr = res->start;
 	pmem->size = resource_size(res);
-	if (!IS_ENABLED(CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE)
-			|| nvdimm_has_flush(nd_region) < 0)
+	fua = nvdimm_has_flush(nd_region);
+	if (!IS_ENABLED(CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE) || fua < 0) {
 		dev_warn(dev, "unable to guarantee persistence of writes\n");
+		fua = 0;
+	}
+	wbc = nvdimm_has_cache(nd_region);
 
 	if (!devm_request_mem_region(dev, res->start, resource_size(res),
 				dev_name(&ndns->dev))) {
@@ -361,7 +364,7 @@ static int pmem_attach_disk(struct devic
 		return PTR_ERR(addr);
 	pmem->virt_addr = addr;
 
-	blk_queue_write_cache(q, true, true);
+	blk_queue_write_cache(q, wbc, fua);
 	blk_queue_make_request(q, pmem_make_request);
 	blk_queue_physical_block_size(q, PAGE_SIZE);
 	blk_queue_logical_block_size(q, pmem_sector_size(ndns));
@@ -391,7 +394,7 @@ static int pmem_attach_disk(struct devic
 		put_disk(disk);
 		return -ENOMEM;
 	}
-	dax_write_cache(dax_dev, true);
+	dax_write_cache(dax_dev, wbc);
 	pmem->dax_dev = dax_dev;
 
 	gendev = disk_to_dev(disk);
--- a/drivers/nvdimm/region_devs.c
+++ b/drivers/nvdimm/region_devs.c
@@ -1092,6 +1092,12 @@ int nvdimm_has_flush(struct nd_region *n
 }
 EXPORT_SYMBOL_GPL(nvdimm_has_flush);
 
+int nvdimm_has_cache(struct nd_region *nd_region)
+{
+	return is_nd_pmem(&nd_region->dev);
+}
+EXPORT_SYMBOL_GPL(nvdimm_has_cache);
+
 void __exit nd_region_devs_exit(void)
 {
 	ida_destroy(&region_ida);
--- a/include/linux/libnvdimm.h
+++ b/include/linux/libnvdimm.h
@@ -170,4 +170,5 @@ void nd_region_release_lane(struct nd_re
 u64 nd_fletcher64(void *addr, size_t len, bool le);
 void nvdimm_flush(struct nd_region *nd_region);
 int nvdimm_has_flush(struct nd_region *nd_region);
+int nvdimm_has_cache(struct nd_region *nd_region);
 #endif /* __LIBNVDIMM_H__ */