x86: ich9: let firmware negotiate 'CPU hot-unplug with SMI' feature

Keep CPU hotunplug with SMI disabled on 5.2 and older and enable
it by default on newer machine types.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Message-Id: <20201207140739.3829993-9-imammedo@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/i386/pc.c

@@ -97,7 +97,9 @@
 #include "trace.h"
 #include CONFIG_DEVICES
 
-GlobalProperty pc_compat_5_2[] = {};
+GlobalProperty pc_compat_5_2[] = {
+    { "ICH9-LPC", "x-smi-cpu-hotunplug", "off" },
+};
 const size_t pc_compat_5_2_len = G_N_ELEMENTS(pc_compat_5_2);
 
 GlobalProperty pc_compat_5_1[] = {

hw/isa/lpc_ich9.c

@@ -392,6 +392,12 @@ static void smi_features_ok_callback(void *opaque)
         return;
     }
 
+    if (guest_cpu_hotplug_features ==
+        BIT_ULL(ICH9_LPC_SMI_F_CPU_HOT_UNPLUG_BIT)) {
+        /* cpu hot-unplug is unsupported without cpu-hotplug */
+        return;
+    }
+
     /* valid feature subset requested, lock it down, report success */
     lpc->smi_negotiated_features = guest_features;
     lpc->smi_features_ok = 1;
@@ -774,7 +780,7 @@ static Property ich9_lpc_properties[] = {
     DEFINE_PROP_BIT64("x-smi-cpu-hotplug", ICH9LPCState, smi_host_features,
                       ICH9_LPC_SMI_F_CPU_HOTPLUG_BIT, true),
     DEFINE_PROP_BIT64("x-smi-cpu-hotunplug", ICH9LPCState, smi_host_features,
-                      ICH9_LPC_SMI_F_CPU_HOT_UNPLUG_BIT, false),
+                      ICH9_LPC_SMI_F_CPU_HOT_UNPLUG_BIT, true),
     DEFINE_PROP_END_OF_LIST(),
 };