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, 6 insertions, 6 deletions

diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index dacb6a8418aa..fa26ffd25fa6 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -389,33 +389,33 @@ static ssize_t show_valid_zones(struct device *dev,
 {
         struct memory_block *mem = to_memory_block(dev);
         unsigned long start_pfn, end_pfn;
+        unsigned long valid_start, valid_end, valid_pages;
         unsigned long nr_pages = PAGES_PER_SECTION * sections_per_block;
-        struct page *first_page;
         struct zone *zone;
         int zone_shift = 0;
 
         start_pfn = section_nr_to_pfn(mem->start_section_nr);
         end_pfn = start_pfn + nr_pages;
-        first_page = pfn_to_page(start_pfn);
 
         /* The block contains more than one zone can not be offlined. */
-        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 sprintf(buf, "none\n");
 
-        zone = page_zone(first_page);
+        zone = page_zone(pfn_to_page(valid_start));
+        valid_pages = valid_end - valid_start;
 
         /* MMOP_ONLINE_KEEP */
         sprintf(buf, "%s", zone->name);
 
         /* MMOP_ONLINE_KERNEL */
-        zone_can_shift(start_pfn, nr_pages, ZONE_NORMAL, &zone_shift);
+        zone_can_shift(valid_start, valid_pages, ZONE_NORMAL, &zone_shift);
         if (zone_shift) {
                 strcat(buf, " ");
                 strcat(buf, (zone + zone_shift)->name);
         }
 
         /* MMOP_ONLINE_MOVABLE */
-        zone_can_shift(start_pfn, nr_pages, ZONE_MOVABLE, &zone_shift);
+        zone_can_shift(valid_start, valid_pages, ZONE_MOVABLE, &zone_shift);
         if (zone_shift) {
                 strcat(buf, " ");
                 strcat(buf, (zone + zone_shift)->name);