base/memory, hotplug: fix a kernel oops in show_valid_zones()

Reading a sysfs "memoryN/valid_zones" file leads to the following oops
when the first page of a range is not backed by struct page.
show_valid_zones() assumes that 'start_pfn' is always valid for
page_zone().

 BUG: unable to handle kernel paging request at ffffea017a000000
 IP: show_valid_zones+0x6f/0x160

This issue may happen on x86-64 systems with 64GiB or more memory since
their memory block size is bumped up to 2GiB.  [1] An example of such
systems is desribed below.  0x3240000000 is only aligned by 1GiB and
this memory block starts from 0x3200000000, which is not backed by
struct page.

 BIOS-e820: [mem 0x0000003240000000-0x000000603fffffff] usable

Since test_pages_in_a_zone() already checks holes, fix this issue by
extending this function to return 'valid_start' and 'valid_end' for a
given range.  show_valid_zones() then proceeds with the valid range.

[1] 'Commit bdee237c0343 ("x86: mm: Use 2GB memory block size on
    large-memory x86-64 systems")'

Link: http://lkml.kernel.org/r/20170127222149.30893-3-toshi.kani@hpe.com
Signed-off-by: Toshi Kani <toshi.kani@hpe.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Zhang Zhen <zhenzhang.zhang@huawei.com>
Cc: Reza Arbab <arbab@linux.vnet.ibm.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: <stable@vger.kernel.org>	[4.4+]

Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 15 insertions, 5 deletions

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 1218f73890b6..b8c11e063ff0 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1484,10 +1484,13 @@ bool is_mem_section_removable(unsigned long start_pfn, unsigned long nr_pages)
 
 /*
  * Confirm all pages in a range [start, end) belong to the same zone.
+ * When true, return its valid [start, end).
  */
-int test_pages_in_a_zone(unsigned long start_pfn, unsigned long end_pfn)
+int test_pages_in_a_zone(unsigned long start_pfn, unsigned long end_pfn,
+                         unsigned long *valid_start, unsigned long *valid_end)
 {
         unsigned long pfn, sec_end_pfn;
+        unsigned long start, end;
         struct zone *zone = NULL;
         struct page *page;
         int i;
@@ -1509,14 +1512,20 @@ int test_pages_in_a_zone(unsigned long start_pfn, unsigned long end_pfn)
                         page = pfn_to_page(pfn + i);
                         if (zone && page_zone(page) != zone)
                                 return 0;
+                        if (!zone)
+                                start = pfn + i;
                         zone = page_zone(page);
+                        end = pfn + MAX_ORDER_NR_PAGES;
                 }
         }
 
-        if (zone)
+        if (zone) {
+                *valid_start = start;
+                *valid_end = end;
                 return 1;
-        else
+        } else {
                 return 0;
+        }
 }
 
 /*
@@ -1843,6 +1852,7 @@ static int __ref __offline_pages(unsigned long start_pfn,
         long offlined_pages;
         int ret, drain, retry_max, node;
         unsigned long flags;
+        unsigned long valid_start, valid_end;
         struct zone *zone;
         struct memory_notify arg;
 
@@ -1853,10 +1863,10 @@ static int __ref __offline_pages(unsigned long start_pfn,
                 return -EINVAL;
         /* This makes hotplug much easier...and readable.
            we assume this for now. .*/
-        if (!test_pages_in_a_zone(start_pfn, end_pfn))
+        if (!test_pages_in_a_zone(start_pfn, end_pfn, &valid_start, &valid_end))
                 return -EINVAL;
 
-        zone = page_zone(pfn_to_page(start_pfn));
+        zone = page_zone(pfn_to_page(valid_start));
         node = zone_to_nid(zone);
         nr_pages = end_pfn - start_pfn;