Add a sysfs knob for dax devices to control the memmap_on_memory setting
if the dax device were to be hotplugged as system memory.
The default memmap_on_memory setting for dax devices originating via
pmem or hmem is set to 'false' - i.e. no memmap_on_memory semantics, to
preserve legacy behavior. For dax devices via CXL, the default is on.
The sysfs control allows the administrator to override the above
defaults if needed.
Cc: David Hildenbrand <da...@redhat.com>
Cc: Dan Williams <dan.j.willi...@intel.com>
Cc: Dave Jiang <dave.ji...@intel.com>
Cc: Dave Hansen <dave.han...@linux.intel.com>
Cc: Huang Ying <ying.hu...@intel.com>
Tested-by: Li Zhijian <lizhij...@fujitsu.com>
Reviewed-by: Jonathan Cameron <jonathan.came...@huawei.com>
Reviewed-by: David Hildenbrand <da...@redhat.com>
Signed-off-by: Vishal Verma <vishal.l.ve...@intel.com>
---
drivers/dax/bus.c | 32 ++++++++++++++++++++++++++++++++
Documentation/ABI/testing/sysfs-bus-dax | 17 +++++++++++++++++
2 files changed, 49 insertions(+)
diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
index ce1356ac6dc2..423adee6f802 100644
--- a/drivers/dax/bus.c
+++ b/drivers/dax/bus.c
@@ -1245,6 +1245,37 @@ static ssize_t numa_node_show(struct device *dev,
}
static DEVICE_ATTR_RO(numa_node);
+static ssize_t memmap_on_memory_show(struct device *dev,
+ struct device_attribute *attr, char *buf)
+{
+ struct dev_dax *dev_dax = to_dev_dax(dev);
+
+ return sprintf(buf, "%d\n", dev_dax->memmap_on_memory);
+}
+
+static ssize_t memmap_on_memory_store(struct device *dev,
+ struct device_attribute *attr,
+ const char *buf, size_t len)
+{
+ struct dax_device_driver *dax_drv = to_dax_drv(dev->driver);
+ struct dev_dax *dev_dax = to_dev_dax(dev);
+ ssize_t rc;
+ bool val;
+
+ rc = kstrtobool(buf, &val);
+ if (rc)
+ return rc;
+
+ guard(device)(dev);
+ if (dev_dax->memmap_on_memory != val &&
+ dax_drv->type == DAXDRV_KMEM_TYPE)
+ return -EBUSY;
+ dev_dax->memmap_on_memory = val;
+
+ return len;
+}
+static DEVICE_ATTR_RW(memmap_on_memory);
+
static umode_t dev_dax_visible(struct kobject *kobj, struct attribute *a, int
n)
{
struct device *dev = container_of(kobj, struct device, kobj);
@@ -1271,6 +1302,7 @@ static struct attribute *dev_dax_attributes[] = {
&dev_attr_align.attr,
&dev_attr_resource.attr,
&dev_attr_numa_node.attr,
+ &dev_attr_memmap_on_memory.attr,
NULL,
};
diff --git a/Documentation/ABI/testing/sysfs-bus-dax
b/Documentation/ABI/testing/sysfs-bus-dax
index a61a7b186017..b1fd8bf8a7de 100644
--- a/Documentation/ABI/testing/sysfs-bus-dax
+++ b/Documentation/ABI/testing/sysfs-bus-dax
@@ -149,3 +149,20 @@ KernelVersion: v5.1
Contact: nvd...@lists.linux.dev
Description:
(RO) The id attribute indicates the region id of a dax region.
+
+What: /sys/bus/dax/devices/daxX.Y/memmap_on_memory
+Date: October, 2023
+KernelVersion: v6.8
+Contact: nvd...@lists.linux.dev
+Description:
+ (RW) Control the memmap_on_memory setting if the dax device
+ were to be hotplugged as system memory. This determines whether
+ the 'altmap' for the hotplugged memory will be placed on the
+ device being hotplugged (memmap_on_memory=1) or if it will be
+ placed on regular memory (memmap_on_memory=0). This attribute
+ must be set before the device is handed over to the 'kmem'
+ driver (i.e. hotplugged into system-ram). Additionally, this
+ depends on CONFIG_MHP_MEMMAP_ON_MEMORY, and a globally enabled
+ memmap_on_memory parameter for memory_hotplug. This is
+ typically set on the kernel command line -
+ memory_hotplug.memmap_on_memory set to 'true' or 'force'."
--
2.41.0
