With Linux 4.19-rc1 commit 7d4340bb92a9df78e6e28152f3dd89d9bd82146b,

titled "powerpc/mm: Increase MAX_PHYSMEM_BITS to 128TB with
SPARSEMEM_VMEMMAP config", the PPC64 MAX_PHYSMEM_BITS value has
been bumped up to 47.  The appropriate update has been made in
this patch.
(hbathini@linux.ibm.com)

defs.h

@@ -4073,6 +4073,7 @@ struct efi_memory_desc_t {
 #define _SECTION_SIZE_BITS	24
 #define _MAX_PHYSMEM_BITS	44
 #define _MAX_PHYSMEM_BITS_3_7   46
+#define _MAX_PHYSMEM_BITS_4_19  47
 
 #endif /* PPC64 */
 

ppc64.c

@@ -554,7 +554,10 @@ ppc64_init(int when)
 			ppc64_vmemmap_init();
 
 		machdep->section_size_bits = _SECTION_SIZE_BITS;
-		if (THIS_KERNEL_VERSION >= LINUX(3,7,0))
+		if ((machdep->flags & VMEMMAP) &&
+		    (THIS_KERNEL_VERSION >= LINUX(4,19,0)))
+			machdep->max_physmem_bits = _MAX_PHYSMEM_BITS_4_19;
+		else if (THIS_KERNEL_VERSION >= LINUX(3,7,0))
 			machdep->max_physmem_bits = _MAX_PHYSMEM_BITS_3_7;
 		else
 			machdep->max_physmem_bits = _MAX_PHYSMEM_BITS;