[Skiboot] [PATCH] core/cpu: Fix invalid SMT indexes

[Reza Arbab]

On Mon, Nov 11, 2024 at 09:41:15AM +1000, Nicholas Piggin wrote:
>@@ -1205,8 +1207,27 @@ void init_cpu_max_pir(void)
> 		 */
> 		pir = dt_prop_get_u32_def(cpu, "ibm,pir", server_no);
>
>-		if (cpu_max_pir < pir + cpu_thread_count - 1)
>-			cpu_max_pir = pir + cpu_thread_count - 1;
>+		p = dt_find_property(cpu, "ibm,ppc-interrupt-server#s");
>+		if (!p)
>+			continue;
>+		threads = p->len / 4;
>+		assert(threads > 0);
>+		if (threads > cpu_threads_max) {
>+			prlog(PR_WARNING, "CPU: Threads out of range for PIR 0x%04x"
>+			      " threads=%d max=%d\n",
>+			      pir, threads, cpu_threads_max);
>+			threads = cpu_threads_max;
>+		}
>+		if (!cpu_thread_count) {
>+			cpu_thread_count = threads;
>+		} else {
>+			/* Do not support asymmetric SMT topologies */
>+			assert(cpu_thread_count == threads);
>+		}
>+

I see, discover the number of threads at runtime, but cap to the 
hardcoded hardware maximum, and disallow a mix of cpus with different 
thread counts.

Exercised a bit with `qemu -smp threads=...`. LGTM!

Applied to master.

-- 
Reza Arbab