mm: teach pfn_to_online_page() to consider subsection validity

pfn_to_online_page is primarily used to filter out offline or fully
uninitialized pages.  pfn_valid resp.  online_section_nr have a coarse
per memory section granularity.  If a section shared with a partially
offline memory (e.g.  part of ZONE_DEVICE) then pfn_to_online_page
would lead to a false positive on some pfns.  Fix this by adding
pfn_section_valid check which is subsection aware.

[mhocko@kernel.org: changelog rewrite]

Link: https://lkml.kernel.org/r/161058500148.1840162.4365921007820501696.stgit@dwillia2-desk3.amr.corp.intel.com
Fixes: b13bc35193d9 ("mm/hotplug: invalid PFNs from pfn_to_online_page()")
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Reported-by: David Hildenbrand <david@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Qian Cai <cai@lca.pw>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
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 fc6cdd9..02378f1 100644 (file)
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -308,11 +308,26 @@ 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) && !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);