powerpc/smp: Adjust nr_cpu_ids to cover all threads of a core

If nr_cpu_ids is too low to include at least all the threads of a single
core adjust nr_cpu_ids upwards. This avoids triggering odd bugs in code
that assumes all threads of a core are available.

Cc: stable@vger.kernel.org
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20231229120107.2281153-1-mpe@ellerman.id.au

arch/powerpc/kernel/prom.c

@@ -375,6 +375,12 @@ static int __init early_init_dt_scan_cpus(unsigned long node,
 	if (IS_ENABLED(CONFIG_PPC64))
 		boot_cpu_hwid = be32_to_cpu(intserv[found_thread]);
 
+	if (nr_cpu_ids % nthreads != 0) {
+		set_nr_cpu_ids(ALIGN(nr_cpu_ids, nthreads));
+		pr_warn("nr_cpu_ids was not a multiple of threads_per_core, adjusted to %d\n",
+			nr_cpu_ids);
+	}
+
 	/*
 	 * PAPR defines "logical" PVR values for cpus that
 	 * meet various levels of the architecture: