libnvdimm, pfn: fix memmap reservation size versus 4K alignment

When vmemmap_populate() allocates space for the memmap it does so in 2MB
sized chunks. The libnvdimm-pfn driver incorrectly accounts for this
when the alignment of the device is set to 4K. When this happens we
trigger memory allocation failures in altmap_alloc_block_buf() and
trigger warnings of the form:

 WARNING: CPU: 0 PID: 3376 at arch/x86/mm/init_64.c:656 arch_add_memory+0xe4/0xf0
 [..]
 Call Trace:
  dump_stack+0x86/0xc3
  __warn+0xcb/0xf0
  warn_slowpath_null+0x1d/0x20
  arch_add_memory+0xe4/0xf0
  devm_memremap_pages+0x29b/0x4e0

Fixes: 315c562536c4 ("libnvdimm, pfn: add 'align' attribute, default to HPAGE_SIZE")
Cc: <stable@vger.kernel.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

1 files changed, 2 insertions, 5 deletions

diff --git a/drivers/nvdimm/pfn_devs.c b/drivers/nvdimm/pfn_devs.c
index a2ac9e641aa9..6c033c9a2f06 100644
--- a/drivers/nvdimm/pfn_devs.c
+++ b/drivers/nvdimm/pfn_devs.c
@@ -627,15 +627,12 @@ static int nd_pfn_init(struct nd_pfn *nd_pfn)
         size = resource_size(&nsio->res);
         npfns = (size - start_pad - end_trunc - SZ_8K) / SZ_4K;
         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, HPAGE_SIZE);
-                offset = ALIGN(start + SZ_8K + memmap_size + dax_label_reserve,
-                                nd_pfn->align) - start;
+                offset = ALIGN(start + SZ_8K + 64 * npfns + dax_label_reserve,
+                                max(nd_pfn->align, HPAGE_SIZE)) - start;
         } else if (nd_pfn->mode == PFN_MODE_RAM)
                 offset = ALIGN(start + SZ_8K + dax_label_reserve,
                                 nd_pfn->align) - start;