q35: catch invalid cpu hotplug configuration

Related: https://bugzilla.redhat.com//show_bug.cgi?id=1985924
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Message-Id: <20210812102341.3316254-1-kraxel@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/isa/lpc_ich9.c

@@ -31,6 +31,7 @@
 #include "qemu/osdep.h"
 #include "qemu/log.h"
 #include "cpu.h"
+#include "qapi/error.h"
 #include "qapi/visitor.h"
 #include "qemu/range.h"
 #include "hw/isa/isa.h"
@@ -676,6 +677,18 @@ static void ich9_lpc_realize(PCIDevice *d, Error **errp)
     DeviceState *dev = DEVICE(d);
     ISABus *isa_bus;
 
+    if ((lpc->smi_host_features & BIT_ULL(ICH9_LPC_SMI_F_CPU_HOT_UNPLUG_BIT)) &&
+        !(lpc->smi_host_features & BIT_ULL(ICH9_LPC_SMI_F_CPU_HOTPLUG_BIT))) {
+        /*
+         * smi_features_ok_callback() throws an error on this.
+         *
+         * So bail out here instead of advertizing the invalid
+         * configuration and get obscure firmware failures from that.
+         */
+        error_setg(errp, "cpu hot-unplug requires cpu hot-plug");
+        return;
+    }
+
     isa_bus = isa_bus_new(DEVICE(d), get_system_memory(), get_system_io(),
                           errp);
     if (!isa_bus) {