[v7 0/3] "Hotremove" persistent memory

[v7 0/3] "Hotremove" persistent memory

[Pavel Tatashin]

Changelog:
v7
- Added Dan Williams Reviewed-by to the last patch, and small change to
  dev_err() otput format as was suggested by Dan.

v6
- A few minor changes and added reviewed-by's.
- Spent time studying lock ordering issue that was reported by Vishal
  Verma, but that issue already exists in Linux, and can be reproduced
  with exactly the same steps with ACPI memory hotplugging.

v5
- Addressed comments from Dan Williams: made remove_memory() to return
  an error code, and use this function from dax.

v4
- Addressed comments from Dave Hansen

v3
- Addressed comments from David Hildenbrand. Don't release
  lock_device_hotplug after checking memory status, and rename
  memblock_offlined_cb() to check_memblock_offlined_cb()

v2
- Dan Williams mentioned that drv->remove() return is ignored
  by unbind. Unbind always succeeds. Because we cannot guarantee
  that memory can be offlined from the driver, don't even
  attempt to do so. Simply check that every section is offlined
  beforehand and only then proceed with removing dax memory.

---

Recently, adding a persistent memory to be used like a regular RAM was
added to Linux. This work extends this functionality to also allow hot
removing persistent memory.

We (Microsoft) have an important use case for this functionality.

The requirement is for physical machines with small amount of RAM (~8G)
to be able to reboot in a very short period of time (<1s). Yet, there is
a userland state that is expensive to recreate (~2G).

The solution is to boot machines with 2G preserved for persistent
memory.

Copy the state, and hotadd the persistent memory so machine still has
all 8G available for runtime. Before reboot, offline and hotremove
device-dax 2G, copy the memory that is needed to be preserved to pmem0
device, and reboot.

The series of operations look like this:

1. After boot restore /dev/pmem0 to ramdisk to be consumed by apps.
   and free ramdisk.
2. Convert raw pmem0 to devdax
   ndctl create-namespace --mode devdax --map mem -e namespace0.0 -f
3. Hotadd to System RAM
   echo dax0.0 > /sys/bus/dax/drivers/device_dax/unbind
   echo dax0.0 > /sys/bus/dax/drivers/kmem/new_id
   echo online_movable > /sys/devices/system/memoryXXX/state
4. Before reboot hotremove device-dax memory from System RAM
   echo offline > /sys/devices/system/memoryXXX/state
   echo dax0.0 > /sys/bus/dax/drivers/kmem/unbind
5. Create raw pmem0 device
   ndctl create-namespace --mode raw  -e namespace0.0 -f
6. Copy the state that was stored by apps to ramdisk to pmem device
7. Do kexec reboot or reboot through firmware if firmware does not
   zero memory in pmem0 region (These machines have only regular
   volatile memory). So to have pmem0 device either memmap kernel
   parameter is used, or devices nodes in dtb are specified.


Pavel Tatashin (3):
  device-dax: fix memory and resource leak if hotplug fails
  mm/hotplug: make remove_memory() interface useable
  device-dax: "Hotremove" persistent memory that is used like normal RAM

 drivers/dax/dax-private.h      |  2 ++
 drivers/dax/kmem.c             | 46 +++++++++++++++++++++---
 include/linux/memory_hotplug.h |  8 +++--
 mm/memory_hotplug.c            | 64 +++++++++++++++++++++++-----------
 4 files changed, 92 insertions(+), 28 deletions(-)

-- 
2.22.0

[v7 1/3] device-dax: fix memory and resource leak if hotplug fails

[Pavel Tatashin]

When add_memory() function fails, the resource and the memory should be
freed.

Fixes: c221c0b0308f ("device-dax: "Hotplug" persistent memory for use like normal RAM")

Signed-off-by: Pavel Tatashin <pasha.tatashin@soleen.com>
Reviewed-by: Dave Hansen <dave.hansen@intel.com>
---
 drivers/dax/kmem.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
index a02318c6d28a..4c0131857133 100644
--- a/drivers/dax/kmem.c
+++ b/drivers/dax/kmem.c
@@ -66,8 +66,11 @@ int dev_dax_kmem_probe(struct device *dev)
 	new_res->name = dev_name(dev);
 
 	rc = add_memory(numa_node, new_res->start, resource_size(new_res));
-	if (rc)
+	if (rc) {
+		release_resource(new_res);
+		kfree(new_res);
 		return rc;
+	}
 
 	return 0;
 }
-- 
2.22.0

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[v7 1/3] device-dax: fix memory and resource leak if hotplug fails

[Pavel Tatashin]

When add_memory() function fails, the resource and the memory should be
freed.

Fixes: c221c0b0308f ("device-dax: "Hotplug" persistent memory for use like normal RAM")

Signed-off-by: Pavel Tatashin <pasha.tatashin@soleen.com>
Reviewed-by: Dave Hansen <dave.hansen@intel.com>
---
 drivers/dax/kmem.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
index a02318c6d28a..4c0131857133 100644
--- a/drivers/dax/kmem.c
+++ b/drivers/dax/kmem.c
@@ -66,8 +66,11 @@ int dev_dax_kmem_probe(struct device *dev)
 	new_res->name = dev_name(dev);
 
 	rc = add_memory(numa_node, new_res->start, resource_size(new_res));
-	if (rc)
+	if (rc) {
+		release_resource(new_res);
+		kfree(new_res);
 		return rc;
+	}
 
 	return 0;
 }
-- 
2.22.0

[v7 2/3] mm/hotplug: make remove_memory() interface useable

[Pavel Tatashin]

As of right now remove_memory() interface is inherently broken. It tries
to remove memory but panics if some memory is not offline. The problem
is that it is impossible to ensure that all memory blocks are offline as
this function also takes lock_device_hotplug that is required to
change memory state via sysfs.

So, between calling this function and offlining all memory blocks there
is always a window when lock_device_hotplug is released, and therefore,
there is always a chance for a panic during this window.

Make this interface to return an error if memory removal fails. This way
it is safe to call this function without panicking machine, and also
makes it symmetric to add_memory() which already returns an error.

Signed-off-by: Pavel Tatashin <pasha.tatashin@soleen.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Acked-by: Michal Hocko <mhocko@suse.com>
---
 include/linux/memory_hotplug.h |  8 +++--
 mm/memory_hotplug.c            | 64 +++++++++++++++++++++++-----------
 2 files changed, 49 insertions(+), 23 deletions(-)

diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index ae892eef8b82..988fde33cd7f 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -324,7 +324,7 @@ static inline void pgdat_resize_init(struct pglist_data *pgdat) {}
 extern bool is_mem_section_removable(unsigned long pfn, unsigned long nr_pages);
 extern void try_offline_node(int nid);
 extern int offline_pages(unsigned long start_pfn, unsigned long nr_pages);
-extern void remove_memory(int nid, u64 start, u64 size);
+extern int remove_memory(int nid, u64 start, u64 size);
 extern void __remove_memory(int nid, u64 start, u64 size);
 
 #else
@@ -341,7 +341,11 @@ static inline int offline_pages(unsigned long start_pfn, unsigned long nr_pages)
 	return -EINVAL;
 }
 
-static inline void remove_memory(int nid, u64 start, u64 size) {}
+static inline int remove_memory(int nid, u64 start, u64 size)
+{
+	return -EBUSY;
+}
+
 static inline void __remove_memory(int nid, u64 start, u64 size) {}
 #endif /* CONFIG_MEMORY_HOTREMOVE */
 
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index e096c987d261..77d1f69cdead 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1736,9 +1736,10 @@ static int check_memblock_offlined_cb(struct memory_block *mem, void *arg)
 		endpa = PFN_PHYS(section_nr_to_pfn(mem->end_section_nr + 1))-1;
 		pr_warn("removing memory fails, because memory [%pa-%pa] is onlined\n",
 			&beginpa, &endpa);
-	}
 
-	return ret;
+		return -EBUSY;
+	}
+	return 0;
 }
 
 static int check_cpu_on_node(pg_data_t *pgdat)
@@ -1821,19 +1822,9 @@ static void __release_memory_resource(resource_size_t start,
 	}
 }
 
-/**
- * remove_memory
- * @nid: the node ID
- * @start: physical address of the region to remove
- * @size: size of the region to remove
- *
- * NOTE: The caller must call lock_device_hotplug() to serialize hotplug
- * and online/offline operations before this call, as required by
- * try_offline_node().
- */
-void __ref __remove_memory(int nid, u64 start, u64 size)
+static int __ref try_remove_memory(int nid, u64 start, u64 size)
 {
-	int ret;
+	int rc = 0;
 
 	BUG_ON(check_hotplug_memory_range(start, size));
 
@@ -1841,13 +1832,13 @@ void __ref __remove_memory(int nid, u64 start, u64 size)
 
 	/*
 	 * All memory blocks must be offlined before removing memory.  Check
-	 * whether all memory blocks in question are offline and trigger a BUG()
+	 * whether all memory blocks in question are offline and return error
 	 * if this is not the case.
 	 */
-	ret = walk_memory_range(PFN_DOWN(start), PFN_UP(start + size - 1), NULL,
-				check_memblock_offlined_cb);
-	if (ret)
-		BUG();
+	rc = walk_memory_range(PFN_DOWN(start), PFN_UP(start + size - 1), NULL,
+			       check_memblock_offlined_cb);
+	if (rc)
+		goto done;
 
 	/* remove memmap entry */
 	firmware_map_remove(start, start + size, "System RAM");
@@ -1859,14 +1850,45 @@ void __ref __remove_memory(int nid, u64 start, u64 size)
 
 	try_offline_node(nid);
 
+done:
 	mem_hotplug_done();
+	return rc;
 }
 
-void remove_memory(int nid, u64 start, u64 size)
+/**
+ * remove_memory
+ * @nid: the node ID
+ * @start: physical address of the region to remove
+ * @size: size of the region to remove
+ *
+ * NOTE: The caller must call lock_device_hotplug() to serialize hotplug
+ * and online/offline operations before this call, as required by
+ * try_offline_node().
+ */
+void __remove_memory(int nid, u64 start, u64 size)
+{
+
+	/*
+	 * trigger BUG() is some memory is not offlined prior to calling this
+	 * function
+	 */
+	if (try_remove_memory(nid, start, size))
+		BUG();
+}
+
+/*
+ * Remove memory if every memory block is offline, otherwise return -EBUSY is
+ * some memory is not offline
+ */
+int remove_memory(int nid, u64 start, u64 size)
 {
+	int rc;
+
 	lock_device_hotplug();
-	__remove_memory(nid, start, size);
+	rc  = try_remove_memory(nid, start, size);
 	unlock_device_hotplug();
+
+	return rc;
 }
 EXPORT_SYMBOL_GPL(remove_memory);
 #endif /* CONFIG_MEMORY_HOTREMOVE */
-- 
2.22.0

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[v7 2/3] mm/hotplug: make remove_memory() interface useable

[Pavel Tatashin]

As of right now remove_memory() interface is inherently broken. It tries
to remove memory but panics if some memory is not offline. The problem
is that it is impossible to ensure that all memory blocks are offline as
this function also takes lock_device_hotplug that is required to
change memory state via sysfs.

So, between calling this function and offlining all memory blocks there
is always a window when lock_device_hotplug is released, and therefore,
there is always a chance for a panic during this window.

Make this interface to return an error if memory removal fails. This way
it is safe to call this function without panicking machine, and also
makes it symmetric to add_memory() which already returns an error.

Signed-off-by: Pavel Tatashin <pasha.tatashin@soleen.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Acked-by: Michal Hocko <mhocko@suse.com>
---
 include/linux/memory_hotplug.h |  8 +++--
 mm/memory_hotplug.c            | 64 +++++++++++++++++++++++-----------
 2 files changed, 49 insertions(+), 23 deletions(-)

diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index ae892eef8b82..988fde33cd7f 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -324,7 +324,7 @@ static inline void pgdat_resize_init(struct pglist_data *pgdat) {}
 extern bool is_mem_section_removable(unsigned long pfn, unsigned long nr_pages);
 extern void try_offline_node(int nid);
 extern int offline_pages(unsigned long start_pfn, unsigned long nr_pages);
-extern void remove_memory(int nid, u64 start, u64 size);
+extern int remove_memory(int nid, u64 start, u64 size);
 extern void __remove_memory(int nid, u64 start, u64 size);
 
 #else
@@ -341,7 +341,11 @@ static inline int offline_pages(unsigned long start_pfn, unsigned long nr_pages)
 	return -EINVAL;
 }
 
-static inline void remove_memory(int nid, u64 start, u64 size) {}
+static inline int remove_memory(int nid, u64 start, u64 size)
+{
+	return -EBUSY;
+}
+
 static inline void __remove_memory(int nid, u64 start, u64 size) {}
 #endif /* CONFIG_MEMORY_HOTREMOVE */
 
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index e096c987d261..77d1f69cdead 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1736,9 +1736,10 @@ static int check_memblock_offlined_cb(struct memory_block *mem, void *arg)
 		endpa = PFN_PHYS(section_nr_to_pfn(mem->end_section_nr + 1))-1;
 		pr_warn("removing memory fails, because memory [%pa-%pa] is onlined\n",
 			&beginpa, &endpa);
-	}
 
-	return ret;
+		return -EBUSY;
+	}
+	return 0;
 }
 
 static int check_cpu_on_node(pg_data_t *pgdat)
@@ -1821,19 +1822,9 @@ static void __release_memory_resource(resource_size_t start,
 	}
 }
 
-/**
- * remove_memory
- * @nid: the node ID
- * @start: physical address of the region to remove
- * @size: size of the region to remove
- *
- * NOTE: The caller must call lock_device_hotplug() to serialize hotplug
- * and online/offline operations before this call, as required by
- * try_offline_node().
- */
-void __ref __remove_memory(int nid, u64 start, u64 size)
+static int __ref try_remove_memory(int nid, u64 start, u64 size)
 {
-	int ret;
+	int rc = 0;
 
 	BUG_ON(check_hotplug_memory_range(start, size));
 
@@ -1841,13 +1832,13 @@ void __ref __remove_memory(int nid, u64 start, u64 size)
 
 	/*
 	 * All memory blocks must be offlined before removing memory.  Check
-	 * whether all memory blocks in question are offline and trigger a BUG()
+	 * whether all memory blocks in question are offline and return error
 	 * if this is not the case.
 	 */
-	ret = walk_memory_range(PFN_DOWN(start), PFN_UP(start + size - 1), NULL,
-				check_memblock_offlined_cb);
-	if (ret)
-		BUG();
+	rc = walk_memory_range(PFN_DOWN(start), PFN_UP(start + size - 1), NULL,
+			       check_memblock_offlined_cb);
+	if (rc)
+		goto done;
 
 	/* remove memmap entry */
 	firmware_map_remove(start, start + size, "System RAM");
@@ -1859,14 +1850,45 @@ void __ref __remove_memory(int nid, u64 start, u64 size)
 
 	try_offline_node(nid);
 
+done:
 	mem_hotplug_done();
+	return rc;
 }
 
-void remove_memory(int nid, u64 start, u64 size)
+/**
+ * remove_memory
+ * @nid: the node ID
+ * @start: physical address of the region to remove
+ * @size: size of the region to remove
+ *
+ * NOTE: The caller must call lock_device_hotplug() to serialize hotplug
+ * and online/offline operations before this call, as required by
+ * try_offline_node().
+ */
+void __remove_memory(int nid, u64 start, u64 size)
+{
+
+	/*
+	 * trigger BUG() is some memory is not offlined prior to calling this
+	 * function
+	 */
+	if (try_remove_memory(nid, start, size))
+		BUG();
+}
+
+/*
+ * Remove memory if every memory block is offline, otherwise return -EBUSY is
+ * some memory is not offline
+ */
+int remove_memory(int nid, u64 start, u64 size)
 {
+	int rc;
+
 	lock_device_hotplug();
-	__remove_memory(nid, start, size);
+	rc  = try_remove_memory(nid, start, size);
 	unlock_device_hotplug();
+
+	return rc;
 }
 EXPORT_SYMBOL_GPL(remove_memory);
 #endif /* CONFIG_MEMORY_HOTREMOVE */
-- 
2.22.0

[v7 3/3] device-dax: "Hotremove" persistent memory that is used like normal RAM

[Pavel Tatashin]

It is now allowed to use persistent memory like a regular RAM, but
currently there is no way to remove this memory until machine is
rebooted.

This work expands the functionality to also allows hotremoving
previously hotplugged persistent memory, and recover the device for use
for other purposes.

To hotremove persistent memory, the management software must first
offline all memory blocks of dax region, and than unbind it from
device-dax/kmem driver. So, operations should look like this:

echo offline > /sys/devices/system/memory/memoryN/state
...
echo dax0.0 > /sys/bus/dax/drivers/kmem/unbind

Note: if unbind is done without offlining memory beforehand, it won't be
possible to do dax0.0 hotremove, and dax's memory is going to be part of
System RAM until reboot.

Signed-off-by: Pavel Tatashin <pasha.tatashin@soleen.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
---
 drivers/dax/dax-private.h |  2 ++
 drivers/dax/kmem.c        | 41 +++++++++++++++++++++++++++++++++++----
 2 files changed, 39 insertions(+), 4 deletions(-)

diff --git a/drivers/dax/dax-private.h b/drivers/dax/dax-private.h
index b4177aafbbd1..9ee659ed5566 100644
--- a/drivers/dax/dax-private.h
+++ b/drivers/dax/dax-private.h
@@ -45,6 +45,7 @@ struct dax_region {
  * @pgmap - pgmap for memmap setup / lifetime (driver owned)
  * @ref: pgmap reference count (driver owned)
  * @cmp: @ref final put completion (driver owned)
+ * @dax_mem_res: physical address range of hotadded DAX memory
  */
 struct dev_dax {
 	struct dax_region *region;
@@ -54,6 +55,7 @@ struct dev_dax {
 	struct dev_pagemap pgmap;
 	struct percpu_ref ref;
 	struct completion cmp;
+	struct resource *dax_kmem_res;
 };
 
 static inline struct dev_dax *to_dev_dax(struct device *dev)
diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
index 4c0131857133..c52a8e5f2345 100644
--- a/drivers/dax/kmem.c
+++ b/drivers/dax/kmem.c
@@ -71,21 +71,54 @@ int dev_dax_kmem_probe(struct device *dev)
 		kfree(new_res);
 		return rc;
 	}
+	dev_dax->dax_kmem_res = new_res;
 
 	return 0;
 }
 
+#ifdef CONFIG_MEMORY_HOTREMOVE
+static int dev_dax_kmem_remove(struct device *dev)
+{
+	struct dev_dax *dev_dax = to_dev_dax(dev);
+	struct resource *res = dev_dax->dax_kmem_res;
+	resource_size_t kmem_start = res->start;
+	resource_size_t kmem_size = resource_size(res);
+	int rc;
+
+	/*
+	 * We have one shot for removing memory, if some memory blocks were not
+	 * offline prior to calling this function remove_memory() will fail, and
+	 * there is no way to hotremove this memory until reboot because device
+	 * unbind will succeed even if we return failure.
+	 */
+	rc = remove_memory(dev_dax->target_node, kmem_start, kmem_size);
+	if (rc) {
+		dev_err(dev,
+			"region %pR cannot be hotremoved, error (%d)\n",
+			res, rc);
+		return rc;
+	}
+
+	/* Release and free dax resources */
+	release_resource(res);
+	kfree(res);
+	dev_dax->dax_kmem_res = NULL;
+
+	return 0;
+}
+#else
 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
+	 * Without hotremove 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;
 }
+#endif /* CONFIG_MEMORY_HOTREMOVE */
 
 static struct dax_device_driver device_dax_kmem_driver = {
 	.drv = {
-- 
2.22.0

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[v7 3/3] device-dax: "Hotremove" persistent memory that is used like normal RAM

[Pavel Tatashin]

It is now allowed to use persistent memory like a regular RAM, but
currently there is no way to remove this memory until machine is
rebooted.

This work expands the functionality to also allows hotremoving
previously hotplugged persistent memory, and recover the device for use
for other purposes.

To hotremove persistent memory, the management software must first
offline all memory blocks of dax region, and than unbind it from
device-dax/kmem driver. So, operations should look like this:

echo offline > /sys/devices/system/memory/memoryN/state
...
echo dax0.0 > /sys/bus/dax/drivers/kmem/unbind

Note: if unbind is done without offlining memory beforehand, it won't be
possible to do dax0.0 hotremove, and dax's memory is going to be part of
System RAM until reboot.

Signed-off-by: Pavel Tatashin <pasha.tatashin@soleen.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
---
 drivers/dax/dax-private.h |  2 ++
 drivers/dax/kmem.c        | 41 +++++++++++++++++++++++++++++++++++----
 2 files changed, 39 insertions(+), 4 deletions(-)

diff --git a/drivers/dax/dax-private.h b/drivers/dax/dax-private.h
index b4177aafbbd1..9ee659ed5566 100644
--- a/drivers/dax/dax-private.h
+++ b/drivers/dax/dax-private.h
@@ -45,6 +45,7 @@ struct dax_region {
  * @pgmap - pgmap for memmap setup / lifetime (driver owned)
  * @ref: pgmap reference count (driver owned)
  * @cmp: @ref final put completion (driver owned)
+ * @dax_mem_res: physical address range of hotadded DAX memory
  */
 struct dev_dax {
 	struct dax_region *region;
@@ -54,6 +55,7 @@ struct dev_dax {
 	struct dev_pagemap pgmap;
 	struct percpu_ref ref;
 	struct completion cmp;
+	struct resource *dax_kmem_res;
 };
 
 static inline struct dev_dax *to_dev_dax(struct device *dev)
diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
index 4c0131857133..c52a8e5f2345 100644
--- a/drivers/dax/kmem.c
+++ b/drivers/dax/kmem.c
@@ -71,21 +71,54 @@ int dev_dax_kmem_probe(struct device *dev)
 		kfree(new_res);
 		return rc;
 	}
+	dev_dax->dax_kmem_res = new_res;
 
 	return 0;
 }
 
+#ifdef CONFIG_MEMORY_HOTREMOVE
+static int dev_dax_kmem_remove(struct device *dev)
+{
+	struct dev_dax *dev_dax = to_dev_dax(dev);
+	struct resource *res = dev_dax->dax_kmem_res;
+	resource_size_t kmem_start = res->start;
+	resource_size_t kmem_size = resource_size(res);
+	int rc;
+
+	/*
+	 * We have one shot for removing memory, if some memory blocks were not
+	 * offline prior to calling this function remove_memory() will fail, and
+	 * there is no way to hotremove this memory until reboot because device
+	 * unbind will succeed even if we return failure.
+	 */
+	rc = remove_memory(dev_dax->target_node, kmem_start, kmem_size);
+	if (rc) {
+		dev_err(dev,
+			"region %pR cannot be hotremoved, error (%d)\n",
+			res, rc);
+		return rc;
+	}
+
+	/* Release and free dax resources */
+	release_resource(res);
+	kfree(res);
+	dev_dax->dax_kmem_res = NULL;
+
+	return 0;
+}
+#else
 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
+	 * Without hotremove 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;
 }
+#endif /* CONFIG_MEMORY_HOTREMOVE */
 
 static struct dax_device_driver device_dax_kmem_driver = {
 	.drv = {
-- 
2.22.0