[PATCH v3 2/2] mm: fix initialization of struct page for holes in memory layout

Mike Rapoport
2021-01-11T19:41:45Z

From: Mike Rapoport <rppt@linux.ibm.com>

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")
Reported-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
---
mm/page_alloc.c | 84 +++++++++++++++++++++++++++++--------------------
1 file changed, 50 insertions(+), 34 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index bdbec4c98173..0b56c3ca354e 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -7077,23 +7077,26 @@ 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_spfn, zone_epfn;
u64 pgcnt = 0;

+ zone_spfn = arch_zone_lowest_possible_pfn[zone];
+ 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++;
}
@@ -7102,51 +7105,64 @@ 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().
+ *
+ * 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
*
- * 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.
+ * 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