mm,memory_hotplug: relax fully spanned sections check

We want {online,offline}_pages to operate on whole memblocks, but
memmap_on_memory will poke pageblock_nr_pages aligned holes in the
beginning, which is a special case we want to allow.  Relax the check to
account for that case.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Oscar Salvador <[email protected]>
Reviewed-by: David Hildenbrand <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Cc: Anshuman Khandual <[email protected]>
Cc: Pavel Tatashin <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

mm/memory_hotplug.c

@@ -838,9 +838,16 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages,
 	int ret;
 	struct memory_notify arg;
 
-	/* We can only online full sections (e.g., SECTION_IS_ONLINE) */
+	/*
+	 * {on,off}lining is constrained to full memory sections (or more
+	 * precisly to memory blocks from the user space POV).
+	 * memmap_on_memory is an exception because it reserves initial part
+	 * of the physical memory space for vmemmaps. That space is pageblock
+	 * aligned.
+	 */
 	if (WARN_ON_ONCE(!nr_pages ||
-			 !IS_ALIGNED(pfn | nr_pages, PAGES_PER_SECTION)))
+			 !IS_ALIGNED(pfn, pageblock_nr_pages) ||
+			 !IS_ALIGNED(pfn + nr_pages, PAGES_PER_SECTION)))
 		return -EINVAL;
 
 	mem_hotplug_begin();
@@ -1573,9 +1580,16 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages)
 	int ret, node;
 	char *reason;
 
-	/* We can only offline full sections (e.g., SECTION_IS_ONLINE) */
+	/*
+	 * {on,off}lining is constrained to full memory sections (or more
+	 * precisly to memory blocks from the user space POV).
+	 * memmap_on_memory is an exception because it reserves initial part
+	 * of the physical memory space for vmemmaps. That space is pageblock
+	 * aligned.
+	 */
 	if (WARN_ON_ONCE(!nr_pages ||
-			 !IS_ALIGNED(start_pfn | nr_pages, PAGES_PER_SECTION)))
+			 !IS_ALIGNED(start_pfn, pageblock_nr_pages) ||
+			 !IS_ALIGNED(start_pfn + nr_pages, PAGES_PER_SECTION)))
 		return -EINVAL;
 
 	mem_hotplug_begin();