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/20210421102701.25051-3-osalvador@suse.de
Signed-off-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: David Hildenbrand <david@redhat.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 729fba1..b8467fa 100644 (file)
--- a/mm/memory_hotplug.c
+++ b/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();