Subject: [RFC PATCH v2 3/5] libnvdimm/dax: Make DAXDEV_SYNC_ENABLED flag region-specific

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Tue, 2 Jun 2020 13:19:07 +0530

This patch makes sync fault enable/disable feature more fine-grained
by allowing region-wise control of the same.

In a followup patch on ppc64 only device with compat string "ibm,pmemory-v2"
will disable the sync fault feature.

Signed-off-by: Aneesh Kumar K.V <[email-masked]>
---
 drivers/dax/bus.c            |  2 +-
 drivers/dax/super.c          | 16 +++++++++-------
 drivers/nvdimm/pmem.c        |  4 ++++
 drivers/nvdimm/region_devs.c | 16 ++++++++++++++++
 include/linux/dax.h          | 16 ++++++++++++++++
 include/linux/libnvdimm.h    |  4 ++++
 6 files changed, 50 insertions(+), 8 deletions(-)

diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
index df238c8b6ef2..8a825ecff49b 100644
--- a/drivers/dax/bus.c
+++ b/drivers/dax/bus.c
@@ -420,7 +420,7 @@ struct dev_dax *__devm_create_dev_dax(struct dax_region *dax_region, int id,
 	 * No 'host' or dax_operations since there is no access to this
 	 * device outside of mmap of the resulting character device.
 	 */
-	dax_dev = alloc_dax(dev_dax, NULL, NULL, DAXDEV_F_SYNC);
+	dax_dev = alloc_dax(dev_dax, NULL, NULL, DAXDEV_F_SYNC | DAXDEV_F_SYNC_ENABLED);
 	if (IS_ERR(dax_dev)) {
 		rc = PTR_ERR(dax_dev);
 		goto err;
diff --git a/drivers/dax/super.c b/drivers/dax/super.c
index 980f7be7e56d..f93e6649d452 100644
--- a/drivers/dax/super.c
+++ b/drivers/dax/super.c
@@ -260,10 +260,11 @@ static ssize_t write_cache_store(struct device *dev,
 }
 static DEVICE_ATTR_RW(write_cache);
 
-static bool dax_synchronous_enabled(struct dax_device *dax_dev)
+bool __dax_synchronous_enabled(struct dax_device *dax_dev)
 {
 	return test_bit(DAXDEV_SYNC_ENABLED, &dax_dev->flags);
 }
+EXPORT_SYMBOL_GPL(__dax_synchronous_enabled);
 
 static void set_dax_synchronous_enable(struct dax_device *dax_dev, bool enable)
 {
@@ -280,6 +281,7 @@ static void set_dax_synchronous_enable(struct dax_device *dax_dev, bool enable)
 static ssize_t sync_fault_show(struct device *dev,
 		struct device_attribute *attr, char *buf)
 {
+	int enabled;
 	struct dax_device *dax_dev = dax_get_by_host(dev_name(dev));
 	ssize_t rc;
 
@@ -287,7 +289,8 @@ static ssize_t sync_fault_show(struct device *dev,
 	if (!dax_dev)
 		return -ENXIO;
 
-	rc = sprintf(buf, "%d\n", !!__dax_synchronous(dax_dev));
+	enabled = (dax_synchronous(dax_dev) && dax_synchronous_enabled(dax_dev));
+	rc = sprintf(buf, "%d\n", enabled);
 	put_dax(dax_dev);
 	return rc;
 }
@@ -461,17 +464,13 @@ EXPORT_SYMBOL_GPL(dax_write_cache_enabled);
 
 bool __dax_synchronous(struct dax_device *dax_dev)
 {
-	return test_bit(DAXDEV_SYNC, &dax_dev->flags) &&
-		test_bit(DAXDEV_SYNC_ENABLED, &dax_dev->flags);
+	return test_bit(DAXDEV_SYNC, &dax_dev->flags);
 }
 EXPORT_SYMBOL_GPL(__dax_synchronous);
 
 void __set_dax_synchronous(struct dax_device *dax_dev)
 {
 	set_bit(DAXDEV_SYNC, &dax_dev->flags);
-#ifndef CONFIG_ARCH_MAP_SYNC_DISABLE
-	set_bit(DAXDEV_SYNC_ENABLED, &dax_dev->flags);
-#endif
 }
 EXPORT_SYMBOL_GPL(__set_dax_synchronous);
 
@@ -665,6 +664,9 @@ struct dax_device *alloc_dax(void *private, const char *__host,
 	if (flags & DAXDEV_F_SYNC)
 		set_dax_synchronous(dax_dev);
 
+	if (flags & DAXDEV_F_SYNC_ENABLED)
+		set_dax_synchronous_enable(dax_dev, true);
+
 	return dax_dev;
 
  err_dev:
diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
index 2df6994acf83..dc9c269eb50d 100644
--- a/drivers/nvdimm/pmem.c
+++ b/drivers/nvdimm/pmem.c
@@ -485,6 +485,10 @@ static int pmem_attach_disk(struct device *dev,
 
 	if (is_nvdimm_sync(nd_region))
 		flags = DAXDEV_F_SYNC;
+
+	if (is_nvdimm_sync_enabled(nd_region))
+		flags |= DAXDEV_F_SYNC_ENABLED;
+
 	dax_dev = alloc_dax(pmem, disk->disk_name, &pmem_dax_ops, flags);
 	if (IS_ERR(dax_dev)) {
 		put_disk(disk);
diff --git a/drivers/nvdimm/region_devs.c b/drivers/nvdimm/region_devs.c
index ccbb5b43b8b2..2181560cf655 100644
--- a/drivers/nvdimm/region_devs.c
+++ b/drivers/nvdimm/region_devs.c
@@ -1283,6 +1283,22 @@ bool is_nvdimm_sync(struct nd_region *nd_region)
 }
 EXPORT_SYMBOL_GPL(is_nvdimm_sync);
 
+bool is_nvdimm_sync_enabled(struct nd_region *nd_region)
+{
+#ifdef CONFIG_ARCH_MAP_SYNC_DISABLE
+	if (is_nd_volatile(&nd_region->dev))
+		return true;
+
+	return is_nd_pmem(&nd_region->dev) &&
+		test_bit(ND_REGION_SYNC_ENABLED, &nd_region->flags);
+#else
+	return true;
+#endif
+
+}
+EXPORT_SYMBOL_GPL(is_nvdimm_sync_enabled);
+
+
 struct conflict_context {
 	struct nd_region *nd_region;
 	resource_size_t start, size;
diff --git a/include/linux/dax.h b/include/linux/dax.h
index d7af5d243f24..c4a3551557de 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -10,6 +10,9 @@
 /* Flag for synchronous flush */
 #define DAXDEV_F_SYNC (1UL << 0)
 
+/* flag for platform forcing synchronous flush disable */
+#define DAXDEV_F_SYNC_ENABLED (1UL << 1)
+
 typedef unsigned long dax_entry_t;
 
 struct iomap_ops;
@@ -59,6 +62,13 @@ static inline void set_dax_synchronous(struct dax_device *dax_dev)
 {
 	__set_dax_synchronous(dax_dev);
 }
+
+bool __dax_synchronous_enabled(struct dax_device *dax_dev);
+static inline bool dax_synchronous_enabled(struct dax_device *dax_dev)
+{
+	return  __dax_synchronous_enabled(dax_dev);
+}
+
 /*
  * Check if given mapping is supported by the file / underlying device.
  */
@@ -69,6 +79,12 @@ static inline bool daxdev_mapping_supported(struct vm_area_struct *vma,
 		return true;
 	if (!IS_DAX(file_inode(vma->vm_file)))
 		return false;
+	/*
+	 * check MAP_SYNC is disabled by platform for this device.
+	 */
+	if (!dax_synchronous_enabled(dax_dev))
+		return false;
+
 	return dax_synchronous(dax_dev);
 }
 #else
diff --git a/include/linux/libnvdimm.h b/include/linux/libnvdimm.h
index 18da4059be09..cc3962c4978f 100644
--- a/include/linux/libnvdimm.h
+++ b/include/linux/libnvdimm.h
@@ -63,6 +63,9 @@ enum {
 	/* Platform provides asynchronous flush mechanism */
 	ND_REGION_ASYNC = 3,
 
+	/* Platform wants to disable synchronous flush mechanism */
+	ND_REGION_SYNC_ENABLED= 4,
+
 	/* mark newly adjusted resources as requiring a label update */
 	DPA_RESOURCE_ADJUSTED = 1 << 0,
 };
@@ -262,6 +265,7 @@ int nvdimm_has_flush(struct nd_region *nd_region);
 int nvdimm_has_cache(struct nd_region *nd_region);
 int nvdimm_in_overwrite(struct nvdimm *nvdimm);
 bool is_nvdimm_sync(struct nd_region *nd_region);
+bool is_nvdimm_sync_enabled(struct nd_region *nd_region);
 
 static inline int nvdimm_ctl(struct nvdimm *nvdimm, unsigned int cmd, void *buf,
 		unsigned int buf_len, int *cmd_rc)
-- 
2.26.2