[PATCH v3 2/6] mm: Teach pfn_to_online_page() to consider subsection validity

[Dan Williams]

pfn_section_valid() determines pfn validity on subsection granularity
where pfn_valid() may be limited to coarse section granularity.
Explicitly validate subsections after pfn_valid() succeeds.

Fixes: b13bc35193d9 ("mm/hotplug: invalid PFNs from pfn_to_online_page()")
Cc: Qian Cai <c...@lca.pw>
Cc: Michal Hocko <mho...@suse.com>
Cc: Oscar Salvador <osalva...@suse.de>
Reported-by: David Hildenbrand <da...@redhat.com>
Signed-off-by: Dan Williams <dan.j.willi...@intel.com>
---
 mm/memory_hotplug.c |   24 ++++++++++++++++++++----
 1 file changed, 20 insertions(+), 4 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 55a69d4396e7..9f37f8a68da4 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -308,11 +308,27 @@ static int check_hotplug_memory_addressable(unsigned long 
pfn,
 struct page *pfn_to_online_page(unsigned long pfn)
 {
        unsigned long nr = pfn_to_section_nr(pfn);
+       struct mem_section *ms;
+
+       if (nr >= NR_MEM_SECTIONS)
+               return NULL;
+
+       ms = __nr_to_section(nr);
+       if (!online_section(ms))
+               return NULL;
+
+       /*
+        * Save some code text when online_section() +
+        * pfn_section_valid() are sufficient.
+        */
+       if (IS_ENABLED(CONFIG_HAVE_ARCH_PFN_VALID))
+               if (!pfn_valid(pfn))
+                       return NULL;
+
+       if (!pfn_section_valid(ms, pfn))
+               return NULL;
 
-       if (nr < NR_MEM_SECTIONS && online_section_nr(nr) &&
-           pfn_valid_within(pfn))
-               return pfn_to_page(pfn);
-       return NULL;
+       return pfn_to_page(pfn);
 }
 EXPORT_SYMBOL_GPL(pfn_to_online_page);