powerpc/mm/numa: skip NUMA_NO_NODE onlining in parse_numa_properties()

Executing node_set_online() when nid = NUMA_NO_NODE results in an
undefined behavior. node_set_online() will call node_set_state(), into
__node_set(), into set_bit(), and since NUMA_NO_NODE is -1 we'll end up
doing a negative shift operation inside
arch/powerpc/include/asm/bitops.h. This potential UB was detected
running a kernel with CONFIG_UBSAN.

The behavior was introduced by commit 10f78fd0da ("powerpc/numa: Fix a
regression on memoryless node 0"), where the check for nid > 0 was
removed to fix a problem that was happening with nid = 0, but the result
is that now we're trying to online NUMA_NO_NODE nids as well.

Checking for nid >= 0 will allow node 0 to be onlined while avoiding
this UB with NUMA_NO_NODE.

Fixes: 10f78fd0da ("powerpc/numa: Fix a regression on memoryless node 0")
Reported-by: Ping Fang <pifang@redhat.com>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220224182312.1012527-1-danielhb413@gmail.com

arch/powerpc/mm/numa.c

@@ -956,7 +956,9 @@ static int __init parse_numa_properties(void)
 			of_node_put(cpu);
 		}
 
-		node_set_online(nid);
+		/* node_set_online() is an UB if 'nid' is negative */
+		if (likely(nid >= 0))
+			node_set_online(nid);
 	}
 
 	get_n_mem_cells(&n_mem_addr_cells, &n_mem_size_cells);