3 files changed, 125 insertions, 0 deletions

diff --git a/drivers/dax/Kconfig b/drivers/dax/Kconfig
index 6fc96f03920e..5ef624fe3934 100644
--- a/drivers/dax/Kconfig
+++ b/drivers/dax/Kconfig
@@ -32,6 +32,22 @@ config DEV_DAX_PMEM
 
           Say M if unsure
 
+config DEV_DAX_KMEM
+        tristate "KMEM DAX: volatile-use of persistent memory"
+        default DEV_DAX
+        depends on DEV_DAX
+        depends on MEMORY_HOTPLUG # for add_memory() and friends
+        help
+          Support access to persistent memory as if it were RAM.  This
+          allows easier use of persistent memory by unmodified
+          applications.
+
+          To use this feature, a DAX device must be unbound from the
+          device_dax driver (PMEM DAX) and bound to this kmem driver
+          on each boot.
+
+          Say N if unsure.
+
 config DEV_DAX_PMEM_COMPAT
         tristate "PMEM DAX: support the deprecated /sys/class/dax interface"
         depends on DEV_DAX_PMEM
diff --git a/drivers/dax/Makefile b/drivers/dax/Makefile
index 233bbffccbe6..81f7d54dadfb 100644
--- a/drivers/dax/Makefile
+++ b/drivers/dax/Makefile
@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0
 obj-$(CONFIG_DAX) += dax.o
 obj-$(CONFIG_DEV_DAX) += device_dax.o
+obj-$(CONFIG_DEV_DAX_KMEM) += kmem.o
 
 dax-y := super.o
 dax-y += bus.o
diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
new file mode 100644
index 000000000000..a02318c6d28a
--- /dev/null
+++ b/drivers/dax/kmem.c
@@ -0,0 +1,108 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright(c) 2016-2019 Intel Corporation. All rights reserved. */
+#include <linux/memremap.h>
+#include <linux/pagemap.h>
+#include <linux/memory.h>
+#include <linux/module.h>
+#include <linux/device.h>
+#include <linux/pfn_t.h>
+#include <linux/slab.h>
+#include <linux/dax.h>
+#include <linux/fs.h>
+#include <linux/mm.h>
+#include <linux/mman.h>
+#include "dax-private.h"
+#include "bus.h"
+
+int dev_dax_kmem_probe(struct device *dev)
+{
+        struct dev_dax *dev_dax = to_dev_dax(dev);
+        struct resource *res = &dev_dax->region->res;
+        resource_size_t kmem_start;
+        resource_size_t kmem_size;
+        resource_size_t kmem_end;
+        struct resource *new_res;
+        int numa_node;
+        int rc;
+
+        /*
+         * Ensure good NUMA information for the persistent memory.
+         * Without this check, there is a risk that slow memory
+         * could be mixed in a node with faster memory, causing
+         * unavoidable performance issues.
+         */
+        numa_node = dev_dax->target_node;
+        if (numa_node < 0) {
+                dev_warn(dev, "rejecting DAX region %pR with invalid node: %d\n",
+                         res, numa_node);
+                return -EINVAL;
+        }
+
+        /* Hotplug starting at the beginning of the next block: */
+        kmem_start = ALIGN(res->start, memory_block_size_bytes());
+
+        kmem_size = resource_size(res);
+        /* Adjust the size down to compensate for moving up kmem_start: */
+        kmem_size -= kmem_start - res->start;
+        /* Align the size down to cover only complete blocks: */
+        kmem_size &= ~(memory_block_size_bytes() - 1);
+        kmem_end = kmem_start + kmem_size;
+
+        /* Region is permanently reserved.  Hot-remove not yet implemented. */
+        new_res = request_mem_region(kmem_start, kmem_size, dev_name(dev));
+        if (!new_res) {
+                dev_warn(dev, "could not reserve region [%pa-%pa]\n",
+                         &kmem_start, &kmem_end);
+                return -EBUSY;
+        }
+
+        /*
+         * Set flags appropriate for System RAM.  Leave ..._BUSY clear
+         * so that add_memory() can add a child resource.  Do not
+         * inherit flags from the parent since it may set new flags
+         * unknown to us that will break add_memory() below.
+         */
+        new_res->flags = IORESOURCE_SYSTEM_RAM;
+        new_res->name = dev_name(dev);
+
+        rc = add_memory(numa_node, new_res->start, resource_size(new_res));
+        if (rc)
+                return rc;
+
+        return 0;
+}
+
+static int dev_dax_kmem_remove(struct device *dev)
+{
+        /*
+         * Purposely leak the request_mem_region() for the device-dax
+         * range and return '0' to ->remove() attempts. The removal of
+         * the device from the driver always succeeds, but the region
+         * is permanently pinned as reserved by the unreleased
+         * request_mem_region().
+         */
+        return 0;
+}
+
+static struct dax_device_driver device_dax_kmem_driver = {
+        .drv = {
+                .probe = dev_dax_kmem_probe,
+                .remove = dev_dax_kmem_remove,
+        },
+};
+
+static int __init dax_kmem_init(void)
+{
+        return dax_driver_register(&device_dax_kmem_driver);
+}
+
+static void __exit dax_kmem_exit(void)
+{
+        dax_driver_unregister(&device_dax_kmem_driver);
+}
+
+MODULE_AUTHOR("Intel Corporation");
+MODULE_LICENSE("GPL v2");
+module_init(dax_kmem_init);
+module_exit(dax_kmem_exit);
+MODULE_ALIAS_DAX_DEVICE(0);