pc: Refuse CPU hotplug if the resulting APIC ID is too large

The ACPI CPU hotplug code requires APIC IDs to be smaller than
ACPI_CPU_HOTPLUG_ID_LIMIT, so enforce the limit before trying to hotplug
a new vCPU, returning an error instead of crashing.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/i386/pc.c

@@ -53,6 +53,7 @@
 #include "qemu/bitmap.h"
 #include "qemu/config-file.h"
 #include "hw/acpi/acpi.h"
+#include "hw/acpi/cpu_hotplug.h"
 #include "hw/cpu/icc_bus.h"
 #include "hw/boards.h"
 #include "hw/pci/pci_host.h"
@@ -974,6 +975,13 @@ void pc_hot_add_cpu(const int64_t id, Error **errp)
         return;
     }
 
+    if (apic_id >= ACPI_CPU_HOTPLUG_ID_LIMIT) {
+        error_setg(errp, "Unable to add CPU: %" PRIi64
+                   ", resulting APIC ID (%" PRIi64 ") is too large",
+                   id, apic_id);
+        return;
+    }
+
     icc_bridge = DEVICE(object_resolve_path_type("icc-bridge",
                                                  TYPE_ICC_BRIDGE, NULL));
     pc_new_cpu(current_cpu_model, apic_id, icc_bridge, errp);