[PATCH] mm/nvdimm: Use correct alignment when looking at first pfn from a region

[Aneesh Kumar K.V]

We already add the start_pad to the resource->start but fails to section
align the start. This make sure with altmap we compute the right first
pfn when start_pad is zero and we are doing an align down of start address.

Signed-off-by: Aneesh Kumar K.V <aneesh.ku...@linux.ibm.com>
---
 kernel/memremap.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/memremap.c b/kernel/memremap.c
index a856cb5ff192..23d77b60e728 100644
--- a/kernel/memremap.c
+++ b/kernel/memremap.c
@@ -59,9 +59,9 @@ static unsigned long pfn_first(struct dev_pagemap *pgmap)
 {
        const struct resource *res = &pgmap->res;
        struct vmem_altmap *altmap = &pgmap->altmap;
-       unsigned long pfn;
+       unsigned long pfn = PHYS_PFN(res->start);
 
-       pfn = res->start >> PAGE_SHIFT;
+       pfn = SECTION_ALIGN_DOWN(pfn);
        if (pgmap->altmap_valid)
                pfn += vmem_altmap_offset(altmap);
        return pfn;
-- 
2.21.0