Commit 73954d37 authored by Vishal Verma's avatar Vishal Verma Committed by Andrew Morton
Browse files

dax: add a sysfs knob to control memmap_on_memory behavior 

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.

Link: https://lkml.kernel.org/r/20240124-vv-dax_abi-v7-5-20d16cb8d23d@intel.com


Signed-off-by: default avatarVishal Verma <vishal.l.verma@intel.com>
Tested-by: default avatarLi Zhijian <lizhijian@fujitsu.com>
Reviewed-by: default avatarJonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: default avatarDavid Hildenbrand <david@redhat.com>
Reviewed-by: default avatarHuang, Ying <ying.huang@intel.com>
Reviewed-by: default avatarAlison Schofield <alison.schofield@intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Oscar Salvador <osalvador@suse.de>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 42d93582

Documentation/ABI/testing/sysfs-bus-dax

+17 −0
Original line number Diff line number Diff line
@@ -134,3 +134,20 @@ KernelVersion: v5.1 
Contact:	nvdimm@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:		January, 2024

KernelVersion:	v6.8

Contact:	nvdimm@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'."

drivers/dax/bus.c

+43 −0
Original line number Diff line number Diff line
@@ -1349,6 +1349,48 @@ 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 sysfs_emit(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 dev_dax *dev_dax = to_dev_dax(dev);

	bool val;

	int rc;



	rc = kstrtobool(buf, &val);

	if (rc)

		return rc;



	if (val == true && !mhp_supports_memmap_on_memory()) {

		dev_dbg(dev, "memmap_on_memory is not available\n");

		return -EOPNOTSUPP;

	}



	rc = down_write_killable(&dax_dev_rwsem);

	if (rc)

		return rc;



	if (dev_dax->memmap_on_memory != val && dev->driver &&

	    to_dax_drv(dev->driver)->type == DAXDRV_KMEM_TYPE) {

		up_write(&dax_dev_rwsem);

		return -EBUSY;

	}



	dev_dax->memmap_on_memory = val;

	up_write(&dax_dev_rwsem);



	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);
@@ -1375,6 +1417,7 @@ 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,

};