[PATCH v1] mm: initialize struct page for reserved pages in ZONE_DEVICE

[Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>]

Reading /proc/kpageflags for pfns allocated by pmem namespace triggers
kernel panic with a message like "BUG: unable to handle kernel paging
request at fffffffffffffffe".

The first few pages (controlled by altmap passed to memmap_init_zone())
in the ZONE_DEVICE can skip struct page initialization, which causes
the reported issue.

This patch simply adds some initialization code for them.

Fixes: 4b94ffdc4163 ("x86, mm: introduce vmem_altmap to augment vmemmap_populate()")
Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
---
 mm/page_alloc.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git v4.17-mmotm-2018-06-07-16-59/mm/page_alloc.c v4.17-mmotm-2018-06-07-16-59_patched/mm/page_alloc.c
index 1772513..0b36afe 100644
--- v4.17-mmotm-2018-06-07-16-59/mm/page_alloc.c
+++ v4.17-mmotm-2018-06-07-16-59_patched/mm/page_alloc.c
@@ -5574,8 +5574,16 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
 	 * Honor reservation requested by the driver for this ZONE_DEVICE
 	 * memory
 	 */
-	if (altmap && start_pfn == altmap->base_pfn)
+	if (altmap && start_pfn == altmap->base_pfn) {
+		unsigned long i;
+
+		for (i = 0; i < altmap->reserve; i++) {
+			page = pfn_to_page(start_pfn + i);
+			__init_single_page(page, start_pfn + i, zone, nid);
+			SetPageReserved(page);
+		}
 		start_pfn += altmap->reserve;
+	}
 
 	for (pfn = start_pfn; pfn < end_pfn; pfn++) {
 		/*
-- 
2.7.0