Index: sys/arm64/acpica/acpi_machdep.c
===================================================================
--- sys/arm64/acpica/acpi_machdep.c
+++ sys/arm64/acpica/acpi_machdep.c
@@ -232,47 +232,12 @@
 static void
 parse_pxm_tables(void *dummy)
 {
-	uint64_t mmfr0, parange;
 
 	/* Only parse ACPI tables when booting via ACPI */
 	if (arm64_bus_method != ARM64_BUS_ACPI)
 		return;
 
-	if (!get_kernel_reg(ID_AA64MMFR0_EL1, &mmfr0)) {
-		/* chosen arbitrarily */
-		mmfr0 = ID_AA64MMFR0_PARange_1T;
-	}
-
-	switch (ID_AA64MMFR0_PARange_VAL(mmfr0)) {
-	case ID_AA64MMFR0_PARange_4G:
-		parange = (vm_paddr_t)4 << 30 /* GiB */;
-		break;
-	case ID_AA64MMFR0_PARange_64G:
-		parange = (vm_paddr_t)64 << 30 /* GiB */;
-		break;
-	case ID_AA64MMFR0_PARange_1T:
-		parange = (vm_paddr_t)1 << 40 /* TiB */;
-		break;
-	case ID_AA64MMFR0_PARange_4T:
-		parange = (vm_paddr_t)4 << 40 /* TiB */;
-		break;
-	case ID_AA64MMFR0_PARange_16T:
-		parange = (vm_paddr_t)16 << 40 /* TiB */;
-		break;
-	case ID_AA64MMFR0_PARange_256T:
-		parange = (vm_paddr_t)256 << 40 /* TiB */;
-		break;
-	case ID_AA64MMFR0_PARange_4P:
-		parange = (vm_paddr_t)4 << 50 /* PiB */;
-		break;
-	default:
-		/* chosen arbitrarily */
-		parange = (vm_paddr_t)1 << 40 /* TiB */;
-		printf("Unknown value for PARange in mmfr0 (%#lx)\n", mmfr0);
-		break;
-	}
-
-	acpi_pxm_init(MAXCPU, parange);
+	acpi_pxm_init(MAXCPU, get_physaddr_max());
 	acpi_pxm_parse_tables();
 	acpi_pxm_set_mem_locality();
 }
Index: sys/arm64/arm64/machdep.c
===================================================================
--- sys/arm64/arm64/machdep.c
+++ sys/arm64/arm64/machdep.c
@@ -910,6 +910,54 @@
 	mtx_lock(&psp->ps_mtx);
 }
 
+/* return the number of physical address bits */
+static inline u_int
+get_physaddr_bits(void)
+{
+	uint64_t mmfr0, parange;
+
+	const int mapping[] = {
+	[ID_AA64MMFR0_PARange_4G]	= 32,
+	[ID_AA64MMFR0_PARange_64G]	= 36,
+	[ID_AA64MMFR0_PARange_1T]	= 40,
+	[ID_AA64MMFR0_PARange_4T]	= 42,
+	[ID_AA64MMFR0_PARange_16T]	= 44,
+	[ID_AA64MMFR0_PARange_256T]	= 48,
+	[ID_AA64MMFR0_PARange_4P]	= 52,
+	/* ensure the last entry is defined */
+	[ID_AA64MMFR0_PARange_MASK]	= 0
+	};
+
+	if (!get_kernel_reg(ID_AA64MMFR0_EL1, &mmfr0)) {
+		printf("WARNING: Unable to retrieve MMRF0 register!\n");
+		/* a conservative default */
+		return (40);
+	}
+	parange = ID_AA64MMFR0_PARange_VAL(mmfr0) >> ID_AA64MMFR0_PARange_SHIFT;
+	if (mapping[parange] == 0) {
+		printf("WARNING: Unknown value for PARange in MMFR0 (%#lx)\n", mmfr0);
+		/* a conservative default */
+		return (40);
+	}
+	return (mapping[parange]);
+}
+
+/* return the number of physical addresses */
+static inline uint64_t
+get_physaddr_count(void)
+{
+
+	return (1ul << get_physaddr_bits());
+}
+
+/* return the maximum valid physical address */
+uint64_t
+get_physaddr_max(void)
+{
+
+	return (get_physaddr_count() - 1);
+}
+
 static void
 init_proc0(vm_offset_t kstack)
 {
Index: sys/arm64/arm64/nexus.c
===================================================================
--- sys/arm64/arm64/nexus.c
+++ sys/arm64/arm64/nexus.c
@@ -163,11 +163,11 @@
 {
 
 	mem_rman.rm_start = 0;
-	mem_rman.rm_end = BUS_SPACE_MAXADDR;
+	mem_rman.rm_end = get_physaddr_max();
 	mem_rman.rm_type = RMAN_ARRAY;
 	mem_rman.rm_descr = "I/O memory addresses";
 	if (rman_init(&mem_rman) ||
-	    rman_manage_region(&mem_rman, 0, BUS_SPACE_MAXADDR))
+	    rman_manage_region(&mem_rman, 0, mem_rman.rm_end))
 		panic("nexus_attach mem_rman");
 	irq_rman.rm_start = 0;
 	irq_rman.rm_end = ~0;
Index: sys/arm64/include/cpu.h
===================================================================
--- sys/arm64/include/cpu.h
+++ sys/arm64/include/cpu.h
@@ -207,6 +207,9 @@
 ADDRESS_TRANSLATE_FUNC(s1e1r)
 ADDRESS_TRANSLATE_FUNC(s1e1w)
 
+/* retrieve the maximum valid physical address */
+extern uint64_t get_physaddr_max(void);
+
 #endif
 
 #endif /* !_MACHINE_CPU_H_ */