hw/acpi/aml-build: Only generate cluster node in PPTT when specified

Currently we'll always generate a cluster node no matter user has
specified '-smp clusters=X' or not. Cluster is an optional level
and will participant the building of Linux scheduling domains and
only appears on a few platforms. It's unncessary to always build
it when it cannot reflect the real topology on platforms having no
cluster implementation and to avoid affecting the linux scheduling
domains in the VM. So only generate the cluster topology in ACPI
PPTT when the user has specified it explicitly in -smp.

Tested qemu-system-aarch64 with `-smp 8` and linux 6.1-rc1, without
this patch:
estuary:/sys/devices/system/cpu/cpu0/topology$ cat cluster_*
ff	# cluster_cpus
0-7	# cluster_cpus_list
56	# cluster_id

with this patch:
estuary:/sys/devices/system/cpu/cpu0/topology$ cat cluster_*
ff	# cluster_cpus
0-7	# cluster_cpus_list
36	# cluster_id, with no cluster node kernel will make it to
	  physical package id

Acked-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Yanan Wang <wangyanan55@huawei.com>
Tested-by: Yanan Wang <wangyanan55@huawei.com>
Signed-off-by: Yicong Yang <yangyicong@hisilicon.com>
Message-Id: <20221229065513.55652-3-yangyicong@huawei.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/acpi/aml-build.c

@@ -2030,7 +2030,7 @@ void build_pptt(GArray *table_data, BIOSLinker *linker, MachineState *ms,
                 0, socket_id, NULL, 0);
         }
 
-        if (mc->smp_props.clusters_supported) {
+        if (mc->smp_props.clusters_supported && mc->smp_props.has_clusters) {
             if (cpus->cpus[n].props.cluster_id != cluster_id) {
                 assert(cpus->cpus[n].props.cluster_id > cluster_id);
                 cluster_id = cpus->cpus[n].props.cluster_id;

hw/core/machine-smp.c

@@ -158,6 +158,8 @@ void machine_parse_smp_config(MachineState *ms,
     ms->smp.threads = threads;
     ms->smp.max_cpus = maxcpus;
 
+    mc->smp_props.has_clusters = config->has_clusters;
+
     /* sanity-check of the computed topology */
     if (sockets * dies * clusters * cores * threads != maxcpus) {
         g_autofree char *topo_msg = cpu_hierarchy_to_string(ms);

include/hw/boards.h

@@ -130,11 +130,14 @@ typedef struct {
  * @prefer_sockets - whether sockets are preferred over cores in smp parsing
  * @dies_supported - whether dies are supported by the machine
  * @clusters_supported - whether clusters are supported by the machine
+ * @has_clusters - whether clusters are explicitly specified in the user
+ *                 provided SMP configuration
  */
 typedef struct {
     bool prefer_sockets;
     bool dies_supported;
     bool clusters_supported;
+    bool has_clusters;
 } SMPCompatProps;
 
 /**

qemu-options.hx

@@ -343,6 +343,9 @@ SRST
     ::
 
         -smp 2
+
+    Note: The cluster topology will only be generated in ACPI and exposed
+    to guest if it's explicitly specified in -smp.
 ERST
 
 DEF("numa", HAS_ARG, QEMU_OPTION_numa,