With POWER10, architecture is adding new pmem flush and sync instructions.
The kernel should prevent the usage of MAP_SYNC if applications are not using
the new instructions on newer hardware
This patch adds a dax attribute
(/sys/bus/nd/devices/region0/pfn0.1/block/pmem0/dax/sync_fault)
which can be used to control this flag. If the device supports synchronous flush
then userspace can update this attribute to enable/disable the synchronous
fault. The attribute is only visible if there is write cache enabled on the
device.
In a followup patch on ppc64 device with compat string "ibm,pmemory-v2"
will disable the sync fault feature.
Signed-off-by: Aneesh Kumar K.V <aneesh.ku...@linux.ibm.com>
---
drivers/dax/bus.c | 2 +-
drivers/dax/super.c | 73 ++++++++++++++++++++++++++++++++++++
drivers/nvdimm/pmem.c | 4 ++
drivers/nvdimm/region_devs.c | 16 ++++++++
include/linux/dax.h | 16 ++++++++
include/linux/libnvdimm.h | 4 ++
mm/Kconfig | 3 ++
7 files changed, 117 insertions(+), 1 deletion(-)
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 8e32345be0f7..f93e6649d452 100644
--- a/drivers/dax/super.c
+++ b/drivers/dax/super.c
@@ -198,6 +198,12 @@ enum dax_device_flags {
DAXDEV_WRITE_CACHE,
/* flag to check if device supports synchronous flush */
DAXDEV_SYNC,
+ /*
+ * flag to indicate whether synchronous flush is enabled.
+ * Some platform may want to disable synchronous flush support
+ * even though device supports the same.
+ */
+ DAXDEV_SYNC_ENABLED,
};
/**
@@ -254,6 +260,63 @@ static ssize_t write_cache_store(struct device *dev,
}
static DEVICE_ATTR_RW(write_cache);
+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)
+{
+ if (!test_bit(DAXDEV_SYNC, &dax_dev->flags))
+ return;
+
+ if (enable)
+ set_bit(DAXDEV_SYNC_ENABLED, &dax_dev->flags);
+ else
+ clear_bit(DAXDEV_SYNC_ENABLED, &dax_dev->flags);
+}
+
+
+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;
+
+ WARN_ON_ONCE(!dax_dev);
+ if (!dax_dev)
+ return -ENXIO;
+
+ enabled = (dax_synchronous(dax_dev) &&
dax_synchronous_enabled(dax_dev));
+ rc = sprintf(buf, "%d\n", enabled);
+ put_dax(dax_dev);
+ return rc;
+}
+
+static ssize_t sync_fault_store(struct device *dev,
+ struct device_attribute *attr, const char *buf, size_t len)
+{
+ bool enable_sync;
+ int rc = strtobool(buf, &enable_sync);
+ struct dax_device *dax_dev = dax_get_by_host(dev_name(dev));
+
+ WARN_ON_ONCE(!dax_dev);
+ if (!dax_dev)
+ return -ENXIO;
+
+ if (rc)
+ len = rc;
+ else
+ set_dax_synchronous_enable(dax_dev, enable_sync);
+
+ put_dax(dax_dev);
+ return len;
+}
+
+static DEVICE_ATTR_RW(sync_fault);
+
static umode_t dax_visible(struct kobject *kobj, struct attribute *a, int n)
{
struct device *dev = container_of(kobj, typeof(*dev), kobj);
@@ -267,11 +330,18 @@ static umode_t dax_visible(struct kobject *kobj, struct
attribute *a, int n)
if (a == &dev_attr_write_cache.attr)
return 0;
#endif
+ if (a == &dev_attr_sync_fault.attr) {
+ if (dax_write_cache_enabled(dax_dev))
+ return a->mode;
+ return 0;
+ }
+
return a->mode;
}
static struct attribute *dax_attributes[] = {
&dev_attr_write_cache.attr,
+ &dev_attr_sync_fault.attr,
NULL,
};
@@ -594,6 +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 97f948f8f4e6..a738b237a3ff 100644
--- a/drivers/nvdimm/pmem.c
+++ b/drivers/nvdimm/pmem.c
@@ -487,6 +487,10 @@ 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 88ea34a9c7fd..d60d159b812b 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 66f6c65bd789..53d4d4b8b6b9 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)
diff --git a/mm/Kconfig b/mm/Kconfig
index cffc276fa19c..aebe7e9c079d 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -868,4 +868,7 @@ config ARCH_HAS_HUGEPD
config MAPPING_DIRTY_HELPERS
bool
+config ARCH_MAP_SYNC_DISABLE
+ bool
+
endmenu
--
2.26.2
