Memory hotplug operations require ranges aligned to memory block
boundaries.  This is a generic operation for hotplug.

Add memory_block_align_range() as a common helper in <linux/memory.h>
that aligns the start address up and end address down to memory block
boundaries.

Update dax/kmem to use this helper.

Signed-off-by: Gregory Price <gourry@gourry.net>
---
 drivers/dax/kmem.c     |  4 +---
 include/linux/memory.h | 22 ++++++++++++++++++++++
 2 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
index eb693a581961..798f389df992 100644
--- a/drivers/dax/kmem.c
+++ b/drivers/dax/kmem.c
@@ -26,9 +26,7 @@ static int dax_kmem_range(struct dev_dax *dev_dax, int i, struct range *r)
 	struct dev_dax_range *dax_range = &dev_dax->ranges[i];
 	struct range *range = &dax_range->range;
 
-	/* memory-block align the hotplug range */
-	r->start = ALIGN(range->start, memory_block_size_bytes());
-	r->end = ALIGN_DOWN(range->end + 1, memory_block_size_bytes()) - 1;
+	*r = memory_block_align_range(range);
 	if (r->start >= r->end) {
 		r->start = range->start;
 		r->end = range->end;
diff --git a/include/linux/memory.h b/include/linux/memory.h
index 5bb5599c6b2b..17cdf6ba3823 100644
--- a/include/linux/memory.h
+++ b/include/linux/memory.h
@@ -20,6 +20,7 @@
 #include <linux/compiler.h>
 #include <linux/mutex.h>
 #include <linux/memory_hotplug.h>
+#include <linux/range.h>
 
 #define MIN_MEMORY_BLOCK_SIZE     (1UL << SECTION_SIZE_BITS)
 
@@ -100,6 +101,27 @@ int arch_get_memory_phys_device(unsigned long start_pfn);
 unsigned long memory_block_size_bytes(void);
 int set_memory_block_size_order(unsigned int order);
 
+/**
+ * memory_block_align_range - align a physical address range to memory blocks
+ * @range: the input range to align
+ *
+ * Aligns the start address up and the end address down to memory block
+ * boundaries. This is required for memory hotplug operations which must
+ * operate on memory-block aligned ranges.
+ *
+ * Returns the aligned range. Callers should check that the returned
+ * range is valid (aligned.start < aligned.end) before using it.
+ */
+static inline struct range memory_block_align_range(const struct range *range)
+{
+	struct range aligned;
+
+	aligned.start = ALIGN(range->start, memory_block_size_bytes());
+	aligned.end = ALIGN_DOWN(range->end + 1, memory_block_size_bytes()) - 1;
+
+	return aligned;
+}
+
 struct memory_notify {
 	unsigned long start_pfn;
 	unsigned long nr_pages;
-- 
2.53.0