libnvdimm, pfn: fix memmap reservation sizing

commit 658922e5 upstream.

When configuring a pfn-device instance to allocate the memmap array it
needs to account for the fact that vmemmap_populate_hugepages()
allocates struct page blocks in HPAGE_SIZE chunks.  We need to align the
reserved area size to 2MB otherwise arch_add_memory() runs out of memory
while establishing the memmap:

 WARNING: CPU: 0 PID: 496 at arch/x86/mm/init_64.c:704 arch_add_memory+0xe7/0xf0
 [..]
 Call Trace:
  [<ffffffff8148bdb3>] dump_stack+0x85/0xc2
  [<ffffffff810a749b>] __warn+0xcb/0xf0
  [<ffffffff810a75cd>] warn_slowpath_null+0x1d/0x20
  [<ffffffff8106a497>] arch_add_memory+0xe7/0xf0
  [<ffffffff811d2097>] devm_memremap_pages+0x287/0x450
  [<ffffffff811d1ffa>] ? devm_memremap_pages+0x1ea/0x450
  [<ffffffffa0000298>] __wrap_devm_memremap_pages+0x58/0x70 [nfit_test_iomap]
  [<ffffffffa0047a58>] pmem_attach_disk+0x318/0x420 [nd_pmem]
  [<ffffffffa0047bcf>] nd_pmem_probe+0x6f/0x90 [nd_pmem]
  [<ffffffffa0009469>] nvdimm_bus_probe+0x69/0x110 [libnvdimm]
 [..]
  ndbus0: nd_pmem.probe(pfn3.0) = -12
 nd_pmem: probe of pfn3.0 failed with error -12
libndctl: ndctl_pfn_enable: pfn3.0: failed to enable
Reported-by: Namratha Kothapalli <namratha.n.kothapalli@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/nvdimm/pmem.c

@@ -314,9 +314,16 @@ static int nd_pfn_init(struct nd_pfn *nd_pfn)
 	 * implementation will limit the pfns advertised through
 	 * ->direct_access() to those that are included in the memmap.
 	 */
-	if (nd_pfn->mode == PFN_MODE_PMEM)
-		offset = ALIGN(SZ_8K + 64 * npfns, nd_pfn->align);
-	else if (nd_pfn->mode == PFN_MODE_RAM)
+	if (nd_pfn->mode == PFN_MODE_PMEM) {
+		unsigned long memmap_size;
+
+		/*
+		 * vmemmap_populate_hugepages() allocates the memmap array in
+		 * HPAGE_SIZE chunks.
+		 */
+		memmap_size = ALIGN(64 * npfns, PMD_SIZE);
+		offset = ALIGN(SZ_8K + memmap_size, nd_pfn->align);
+	} else if (nd_pfn->mode == PFN_MODE_RAM)
 		offset = ALIGN(SZ_8K, nd_pfn->align);
 	else
 		goto err;