[PATCH v4 2/2] mm: fix initialization of struct page for holes in memory layout

[Mike Rapoport]

From: Mike Rapoport <rppt@xxxxxxxxxxxxx>

There could be struct pages that are not backed by actual physical
memory.  This can happen when the actual memory bank is not a multiple
of SECTION_SIZE or when an architecture does not register memory holes
reserved by the firmware as memblock.memory.

Such pages are currently initialized using init_unavailable_mem()
function that iterates through PFNs in holes in memblock.memory and if
there is a struct page corresponding to a PFN, the fields if this page
are set to default values and the page is marked as Reserved.

init_unavailable_mem() does not take into account zone and node the page
belongs to and sets both zone and node links in struct page to zero.

On a system that has firmware reserved holes in a zone above ZONE_DMA,
for instance in a configuration below:

	# grep -A1 E820 /proc/iomem
	7a17b000-7a216fff : Unknown E820 type
	7a217000-7bffffff : System RAM

unset zone link in struct page will trigger

	VM_BUG_ON_PAGE(!zone_spans_pfn(page_zone(page), pfn), page);

because there are pages in both ZONE_DMA32 and ZONE_DMA (unset zone link
in struct page) in the same pageblock.

Update init_unavailable_mem() to use zone constraints defined by an
architecture to properly setup the zone link and use node ID of the
adjacent range in memblock.memory to set the node link.

Fixes: 73a6e474cb37 ("mm: memmap_init: iterate over memblock regions rather that check each PFN")
Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxx>
Reported-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
---
 mm/page_alloc.c | 85 +++++++++++++++++++++++++++++--------------------
 1 file changed, 51 insertions(+), 34 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 519a60d5b6f7..444642393bb6 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -7080,23 +7080,27 @@ void __init free_area_init_memoryless_node(int nid)
  * Initialize all valid struct pages in the range [spfn, epfn) and mark them
  * PageReserved(). Return the number of struct pages that were initialized.
  */
-static u64 __init init_unavailable_range(unsigned long spfn, unsigned long epfn)
+static u64 __init init_unavailable_range(unsigned long spfn, unsigned long epfn,
+					 int zone, int nid)
 {
-	unsigned long pfn;
+	unsigned long pfn, zone_epfn, zone_spfn = 0;
 	u64 pgcnt = 0;
 
+	if (zone)
+		zone_spfn = arch_zone_highest_possible_pfn[zone - 1];
+	zone_epfn = arch_zone_highest_possible_pfn[zone];
+
+	spfn = clamp(spfn, zone_spfn, zone_epfn);
+	epfn = clamp(epfn, zone_spfn, zone_epfn);
+
 	for (pfn = spfn; pfn < epfn; pfn++) {
 		if (!pfn_valid(ALIGN_DOWN(pfn, pageblock_nr_pages))) {
 			pfn = ALIGN_DOWN(pfn, pageblock_nr_pages)
 				+ pageblock_nr_pages - 1;
 			continue;
 		}
-		/*
-		 * Use a fake node/zone (0) for now. Some of these pages
-		 * (in memblock.reserved but not in memblock.memory) will
-		 * get re-initialized via reserve_bootmem_region() later.
-		 */
-		__init_single_page(pfn_to_page(pfn), pfn, 0, 0);
+
+		__init_single_page(pfn_to_page(pfn), pfn, zone, nid);
 		__SetPageReserved(pfn_to_page(pfn));
 		pgcnt++;
 	}
@@ -7105,51 +7109,64 @@ static u64 __init init_unavailable_range(unsigned long spfn, unsigned long epfn)
 }
 
 /*
- * Only struct pages that are backed by physical memory are zeroed and
- * initialized by going through __init_single_page(). But, there are some
- * struct pages which are reserved in memblock allocator and their fields
- * may be accessed (for example page_to_pfn() on some configuration accesses
- * flags). We must explicitly initialize those struct pages.
+ * Only struct pages that correspond to ranges defined by memblock.memory
+ * are zeroed and initialized by going through __init_single_page() during
+ * memmap_init().
  *
- * This function also addresses a similar issue where struct pages are left
- * uninitialized because the physical address range is not covered by
- * memblock.memory or memblock.reserved. That could happen when memblock
- * layout is manually configured via memmap=, or when the highest physical
- * address (max_pfn) does not end on a section boundary.
+ * But, there could be struct pages that correspond to holes in
+ * memblock.memory. This can happen because of the following reasons:
+ * - phyiscal memory bank size is not necessarily the exact multiple of the
+ *   arbitrary section size
+ * - early reserved memory may not be listed in memblock.memory
+ * - memory layouts defined with memmap= kernel parameter may not align
+ *   nicely with memmap sections
+ *
+ * Explicitly initialize those struct pages so that:
+ * - PG_Reserved is set
+ * - zone link is set accorging to the architecture constrains
+ * - node is set to node id of the next populated region except for the
+ *   trailing hole where last node id is used
  */
-static void __init init_unavailable_mem(void)
+static void __init init_zone_unavailable_mem(int zone)
 {
-	phys_addr_t start, end;
-	u64 i, pgcnt;
-	phys_addr_t next = 0;
+	unsigned long start, end;
+	int i, nid;
+	u64 pgcnt;
+	unsigned long next = 0;
 
 	/*
-	 * Loop through unavailable ranges not covered by memblock.memory.
+	 * Loop through holes in memblock.memory and initialize struct
+	 * pages corresponding to these holes
 	 */
 	pgcnt = 0;
-	for_each_mem_range(i, &start, &end) {
+	for_each_mem_pfn_range(i, MAX_NUMNODES, &start, &end, &nid) {
 		if (next < start)
-			pgcnt += init_unavailable_range(PFN_DOWN(next),
-							PFN_UP(start));
+			pgcnt += init_unavailable_range(next, start, zone, nid);
 		next = end;
 	}
 
 	/*
-	 * Early sections always have a fully populated memmap for the whole
-	 * section - see pfn_valid(). If the last section has holes at the
-	 * end and that section is marked "online", the memmap will be
-	 * considered initialized. Make sure that memmap has a well defined
-	 * state.
+	 * Last section may surpass the actual end of memory (e.g. we can
+	 * have 1Gb section and 512Mb of RAM pouplated).
+	 * Make sure that memmap has a well defined state in this case.
 	 */
-	pgcnt += init_unavailable_range(PFN_DOWN(next),
-					round_up(max_pfn, PAGES_PER_SECTION));
+	end = round_up(max_pfn, PAGES_PER_SECTION);
+	pgcnt += init_unavailable_range(next, end, zone, nid);
 
 	/*
 	 * Struct pages that do not have backing memory. This could be because
 	 * firmware is using some of this memory, or for some other reasons.
 	 */
 	if (pgcnt)
-		pr_info("Zeroed struct page in unavailable ranges: %lld pages", pgcnt);
+		pr_info("Zone %s: zeroed struct page in unavailable ranges: %lld pages", zone_names[zone], pgcnt);
+}
+
+static void __init init_unavailable_mem(void)
+{
+	int zone;
+
+	for (zone = 0; zone < ZONE_MOVABLE; zone++)
+		init_zone_unavailable_mem(zone);
 }
 #else
 static inline void __init init_unavailable_mem(void)
-- 
2.28.0