Hotplugged memory has alignmet restrictions. E.g, it disallows all
operations smaller than a sub-section and only allow operations smaller
than a section for SPARSEMEM_VMEMMAP. Export the alignment restrictions
for mhp users.

Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
---
  include/linux/memory_hotplug.h |  5 +++++
  mm/memory_hotplug.c            | 33 +++++++++++++++++++--------------
  2 files changed, 24 insertions(+), 14 deletions(-)

diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index 28f32fd00fe9..c55a9049b11e 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h

@@ -76,6 +76,7 @@ struct mhp_params {
  
  bool mhp_range_allowed(u64 start, u64 size, bool need_mapping);
  struct range mhp_get_pluggable_range(bool need_mapping);
+unsigned long mhp_get_min_align(void);
  
  /*
   * Zone resizing functions

@@ -248,6 +249,10 @@ void mem_hotplug_done(void);
  	___page;				\
   })
  
+static inline unsigned long mhp_get_min_align(void)
+{
+	return 0;
+}
  static inline unsigned zone_span_seqbegin(struct zone *zone)
  {
  	return 0;

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 9e86e9ee0a10..161bb6704a9b 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c

@@ -270,24 +270,29 @@ void __init register_page_bootmem_info_node(struct pglist_data *pgdat)
  }
  #endif /* CONFIG_HAVE_BOOTMEM_INFO_NODE */
  
+/*
+ * Disallow all operations smaller than a sub-section and only
+ * allow operations smaller than a section for
+ * SPARSEMEM_VMEMMAP. Note that check_hotplug_memory_range()
+ * enforces a larger memory_block_size_bytes() granularity for
+ * memory that will be marked online, so this check should only
+ * fire for direct arch_{add,remove}_memory() users outside of
+ * add_memory_resource().
+ */
+unsigned long mhp_get_min_align(void)
+{
+	if (IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP))
+		return PAGES_PER_SUBSECTION;
+	return PAGES_PER_SECTION;
+}
+EXPORT_SYMBOL_GPL(mhp_get_min_align);