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.
Signed-off-by: Aneesh Kumar K.V <aneesh.ku...@linux.ibm.com>
---
drivers/dax/super.c | 73 ++++++++++++++++++++++++++++++++++++++++++++-
mm/Kconfig | 3 ++
2 files changed, 75 insertions(+), 1 deletion(-)
diff --git a/drivers/dax/super.c b/drivers/dax/super.c
index 8e32345be0f7..980f7be7e56d 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 +260,60 @@ 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)
+{
+ return test_bit(DAXDEV_SYNC_ENABLED, &dax_dev->flags);
+}
+
+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)
+{
+ 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;
+
+ rc = sprintf(buf, "%d\n", !!__dax_synchronous(dax_dev));
+ 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 +327,18 @@ 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,
};
@@ -394,13 +461,17 @@ EXPORT_SYMBOL_GPL(dax_write_cache_enabled);
bool __dax_synchronous(struct dax_device *dax_dev)
{
- return test_bit(DAXDEV_SYNC, &dax_dev->flags);
+ return test_bit(DAXDEV_SYNC, &dax_dev->flags) &&
+ test_bit(DAXDEV_SYNC_ENABLED, &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);
diff --git a/mm/Kconfig b/mm/Kconfig
index c1acc34c1c35..38fd7cfbfca8 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -867,4 +867,7 @@ config ARCH_HAS_HUGEPD
config MAPPING_DIRTY_HELPERS
bool
+config ARCH_MAP_SYNC_DISABLE
+ bool
+
endmenu
--
2.26.2
