x86/numa_emulation: Refine the calculation of max_emu_nid and dfl_phys_nid

max_emu_nid and dfl_phys_nid is calculated from emu_nid_to_phys[], which is
calculated in split_nodes_xxx_interleave(). From the logic in these
functions, it is assured the emu_nid_to_phys[] has meaningful value if it
return successfully and ensures dfl_phys_nid will get a valid value.

This patch removes the error branch to check invalid dfl_phys_nid and
abstracts out this part to a function for readability.

Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: bp@alien8.de
Cc: kirill@shutemov.name
Cc: rientjes@google.com
Cc: tj@kernel.org
Link: http://lkml.kernel.org/r/20170708013059.29708-2-richard.weiyang@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/mm/numa_emulation.c

@@ -280,6 +280,22 @@ static int __init split_nodes_size_interleave(struct numa_meminfo *ei,
 	return 0;
 }
 
+int __init setup_emu2phys_nid(int *dfl_phys_nid)
+{
+	int i, max_emu_nid = 0;
+
+	*dfl_phys_nid = NUMA_NO_NODE;
+	for (i = 0; i < ARRAY_SIZE(emu_nid_to_phys); i++) {
+		if (emu_nid_to_phys[i] != NUMA_NO_NODE) {
+			max_emu_nid = i;
+			if (*dfl_phys_nid == NUMA_NO_NODE)
+				*dfl_phys_nid = emu_nid_to_phys[i];
+		}
+	}
+
+	return max_emu_nid;
+}
+
 /**
  * numa_emulation - Emulate NUMA nodes
  * @numa_meminfo: NUMA configuration to massage
@@ -376,19 +392,7 @@ void __init numa_emulation(struct numa_meminfo *numa_meminfo, int numa_dist_cnt)
 	 * Determine the max emulated nid and the default phys nid to use
 	 * for unmapped nodes.
 	 */
-	max_emu_nid = 0;
-	dfl_phys_nid = NUMA_NO_NODE;
-	for (i = 0; i < ARRAY_SIZE(emu_nid_to_phys); i++) {
-		if (emu_nid_to_phys[i] != NUMA_NO_NODE) {
-			max_emu_nid = i;
-			if (dfl_phys_nid == NUMA_NO_NODE)
-				dfl_phys_nid = emu_nid_to_phys[i];
-		}
-	}
-	if (dfl_phys_nid == NUMA_NO_NODE) {
-		pr_warning("NUMA: Warning: can't determine default physical node, disabling emulation\n");
-		goto no_emu;
-	}
+	max_emu_nid = setup_emu2phys_nid(&dfl_phys_nid);
 
 	/* commit */
 	*numa_meminfo = ei;