Vishal Verma <vishal.l.ve...@intel.com> writes:
> 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 | 47
> +++++++++++++++++++++++++++++++++
> Documentation/ABI/testing/sysfs-bus-dax | 17 ++++++++++++
> 2 files changed, 64 insertions(+)
>
> diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
> index 1ff1ab5fa105..2871e5188f0d 100644
> --- a/drivers/dax/bus.c
> +++ b/drivers/dax/bus.c
> @@ -1270,6 +1270,52 @@ 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 device_driver *drv = dev->driver;
> + struct dev_dax *dev_dax = to_dev_dax(dev);
> + struct dax_region *dax_region = dev_dax->region;
> + struct dax_device_driver *dax_drv = to_dax_drv(drv);
> + ssize_t rc;
> + bool val;
> +
> + rc = kstrtobool(buf, &val);
> + if (rc)
> + return rc;
> +
> + if (dev_dax->memmap_on_memory == val)
> + return len;
> +
> + device_lock(dax_region->dev);
> + if (!dax_region->dev->driver) {
> + device_unlock(dax_region->dev);
> + return -ENXIO;
> + }
I think that it should be OK to write to "memmap_on_memory" if no driver
is bound to the device. We just need to avoid to write to it when kmem
driver is bound.
--
Best Regards,
Huang, Ying
> +
> + if (dax_drv->type == DAXDRV_KMEM_TYPE) {
> + device_unlock(dax_region->dev);
> + return -EBUSY;
> + }
> +
> + device_lock(dev);
> + dev_dax->memmap_on_memory = val;
> + device_unlock(dev);
> +
> + device_unlock(dax_region->dev);
> + 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);
> @@ -1296,6 +1342,7 @@ 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'."
