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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: Vishal Verma <vishal.l.verma@intel.com> Tested-by: Li Zhijian <lizhijian@fujitsu.com> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com> Reviewed-by: David Hildenbrand <david@redhat.com> Reviewed-by: Huang, Ying <ying.huang@intel.com> Reviewed-by: Alison 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: Andrew Morton <akpm@linux-foundation.org>
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@ -134,3 +134,20 @@ KernelVersion: v5.1
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Contact: nvdimm@lists.linux.dev
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Description:
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(RO) The id attribute indicates the region id of a dax region.
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What: /sys/bus/dax/devices/daxX.Y/memmap_on_memory
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Date: January, 2024
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KernelVersion: v6.8
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Contact: nvdimm@lists.linux.dev
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Description:
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(RW) Control the memmap_on_memory setting if the dax device
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were to be hotplugged as system memory. This determines whether
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the 'altmap' for the hotplugged memory will be placed on the
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device being hotplugged (memmap_on_memory=1) or if it will be
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placed on regular memory (memmap_on_memory=0). This attribute
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must be set before the device is handed over to the 'kmem'
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driver (i.e. hotplugged into system-ram). Additionally, this
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depends on CONFIG_MHP_MEMMAP_ON_MEMORY, and a globally enabled
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memmap_on_memory parameter for memory_hotplug. This is
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typically set on the kernel command line -
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memory_hotplug.memmap_on_memory set to 'true' or 'force'."
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@ -1349,6 +1349,48 @@ static ssize_t numa_node_show(struct device *dev,
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}
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static DEVICE_ATTR_RO(numa_node);
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static ssize_t memmap_on_memory_show(struct device *dev,
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struct device_attribute *attr, char *buf)
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{
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struct dev_dax *dev_dax = to_dev_dax(dev);
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return sysfs_emit(buf, "%d\n", dev_dax->memmap_on_memory);
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}
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static ssize_t memmap_on_memory_store(struct device *dev,
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struct device_attribute *attr,
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const char *buf, size_t len)
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{
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struct dev_dax *dev_dax = to_dev_dax(dev);
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bool val;
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int rc;
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rc = kstrtobool(buf, &val);
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if (rc)
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return rc;
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if (val == true && !mhp_supports_memmap_on_memory()) {
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dev_dbg(dev, "memmap_on_memory is not available\n");
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return -EOPNOTSUPP;
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}
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rc = down_write_killable(&dax_dev_rwsem);
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if (rc)
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return rc;
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if (dev_dax->memmap_on_memory != val && dev->driver &&
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to_dax_drv(dev->driver)->type == DAXDRV_KMEM_TYPE) {
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up_write(&dax_dev_rwsem);
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return -EBUSY;
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}
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dev_dax->memmap_on_memory = val;
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up_write(&dax_dev_rwsem);
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return len;
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}
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static DEVICE_ATTR_RW(memmap_on_memory);
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static umode_t dev_dax_visible(struct kobject *kobj, struct attribute *a, int n)
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{
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struct device *dev = container_of(kobj, struct device, kobj);
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@ -1375,6 +1417,7 @@ static struct attribute *dev_dax_attributes[] = {
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&dev_attr_align.attr,
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&dev_attr_resource.attr,
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&dev_attr_numa_node.attr,
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&dev_attr_memmap_on_memory.attr,
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NULL,
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};
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