libnvdimm, pfn: fix start_pad handling for aligned namespaces

The alignment checks at pfn driver startup fail to properly account for
the 'start_pad' in the case where the namespace is misaligned relative
to its internal alignment. This is typically triggered in 1G aligned
namespace, but could theoretically trigger with small namespace
alignments. When this triggers the kernel reports messages of the form:

    dax2.1: bad offset: 0x3c000000 dax disabled align: 0x40000000

Cc: <stable@vger.kernel.org>
Fixes: 1ee6667c ("libnvdimm, pfn, dax: fix initialization vs autodetect...")
Reported-by: Jane Chu <jane.chu@oracle.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/nvdimm/pfn_devs.c

@@ -364,9 +364,9 @@ struct device *nd_pfn_create(struct nd_region *nd_region)
 int nd_pfn_validate(struct nd_pfn *nd_pfn, const char *sig)
 {
 	u64 checksum, offset;
-	unsigned long align;
 	enum nd_pfn_mode mode;
 	struct nd_namespace_io *nsio;
+	unsigned long align, start_pad;
 	struct nd_pfn_sb *pfn_sb = nd_pfn->pfn_sb;
 	struct nd_namespace_common *ndns = nd_pfn->ndns;
 	const u8 *parent_uuid = nd_dev_to_uuid(&ndns->dev);
@@ -410,6 +410,7 @@ int nd_pfn_validate(struct nd_pfn *nd_pfn, const char *sig)
 
 	align = le32_to_cpu(pfn_sb->align);
 	offset = le64_to_cpu(pfn_sb->dataoff);
+	start_pad = le32_to_cpu(pfn_sb->start_pad);
 	if (align == 0)
 		align = 1UL << ilog2(offset);
 	mode = le32_to_cpu(pfn_sb->mode);
@@ -468,7 +469,7 @@ int nd_pfn_validate(struct nd_pfn *nd_pfn, const char *sig)
 		return -EBUSY;
 	}
 
-	if ((align && !IS_ALIGNED(offset, align))
+	if ((align && !IS_ALIGNED(nsio->res.start + offset + start_pad, align))
 			|| !IS_ALIGNED(offset, PAGE_SIZE)) {
 		dev_err(&nd_pfn->dev,
 				"bad offset: %#llx dax disabled align: %#lx\n",