libnvdimm, dax: fix 1GB-aligned namespaces vs physical misalignment

The following namespace configuration attempt:

    # ndctl create-namespace -e namespace0.0 -m devdax -a 1G -f
    libndctl: ndctl_dax_enable: dax0.1: failed to enable
      Error: namespace0.0: failed to enable

    failed to reconfigure namespace: No such device or address

...fails when the backing memory range is not physically aligned to 1G:

    # cat /proc/iomem | grep Persistent
    210000000-30fffffff : Persistent Memory (legacy)

In the above example the 4G persistent memory range starts and ends on a
256MB boundary.

We handle this case correctly when needing to handle cases that violate
section alignment (128MB) collisions against "System RAM", and we simply
need to extend that padding/truncation for the 1GB alignment use case.

Cc: <stable@vger.kernel.org>
Fixes: 315c5625 ("libnvdimm, pfn: add 'align' attribute...")
Reported-and-tested-by: NJane Chu <jane.chu@oracle.com>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

drivers/nvdimm/pfn_devs.c

@@ -583,6 +583,12 @@ static struct vmem_altmap *__nvdimm_setup_pfn(struct nd_pfn *nd_pfn,
 	return altmap;
 }
 
+static u64 phys_pmem_align_down(struct nd_pfn *nd_pfn, u64 phys)
+{
+	return min_t(u64, PHYS_SECTION_ALIGN_DOWN(phys),
+			ALIGN_DOWN(phys, nd_pfn->align));
+}
+
 static int nd_pfn_init(struct nd_pfn *nd_pfn)
 {
 	u32 dax_label_reserve = is_nd_dax(&nd_pfn->dev) ? SZ_128K : 0;
@@ -638,13 +644,16 @@ static int nd_pfn_init(struct nd_pfn *nd_pfn)
 	start = nsio->res.start;
 	size = PHYS_SECTION_ALIGN_UP(start + size) - start;
 	if (region_intersects(start, size, IORESOURCE_SYSTEM_RAM,
-				IORES_DESC_NONE) == REGION_MIXED) {
+				IORES_DESC_NONE) == REGION_MIXED
+			|| !IS_ALIGNED(start + resource_size(&nsio->res),
+				nd_pfn->align)) {
 		size = resource_size(&nsio->res);
-		end_trunc = start + size - PHYS_SECTION_ALIGN_DOWN(start + size);
+		end_trunc = start + size - phys_pmem_align_down(nd_pfn,
+				start + size);
 	}
 
 	if (start_pad + end_trunc)
-		dev_info(&nd_pfn->dev, "%s section collision, truncate %d bytes\n",
+		dev_info(&nd_pfn->dev, "%s alignment collision, truncate %d bytes\n",
 				dev_name(&ndns->dev), start_pad + end_trunc);
 
 	/*