target-i386: Disable cache info passthrough by default

The host cache information may not make sense for the guest if the VM
CPU topology doesn't match the host CPU topology. To make sure we won't
expose broken cache information to the guest, disable cache info
passthrough by default, and add a new "host-cache-info" property that
can be used to enable the old behavior for users that really need it.

Cc: Benoît Canet <benoit@irqsave.net>
Reviewed-by: NIgor Mammedov <imammedo@redhat.com>
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>

include/hw/i386/pc.h

@@ -318,6 +318,11 @@ bool e820_get_entry(int, uint32_t, uint64_t *, uint64_t *);
             .driver   = "Broadwell-noTSX-" TYPE_X86_CPU,\
             .property = "abm",\
             .value    = "off",\
+        },\
+        {\
+            .driver   = "host" "-" TYPE_X86_CPU,\
+            .property = "host-cache-info",\
+            .value    = "on",\
         },
 
 #define PC_COMPAT_2_3 \

target-i386/cpu.c

@@ -656,7 +656,6 @@ struct X86CPUDefinition {
     int stepping;
     FeatureWordArray features;
     char model_id[48];
-    bool cache_info_passthrough;
 };
 
 static X86CPUDefinition builtin_x86_defs[] = {
@@ -1420,6 +1419,7 @@ static X86CPUDefinition host_cpudef;
 
 static Property host_x86_cpu_properties[] = {
     DEFINE_PROP_BOOL("migratable", X86CPU, migratable, true),
+    DEFINE_PROP_BOOL("host-cache-info", X86CPU, cache_info_passthrough, false),
     DEFINE_PROP_END_OF_LIST()
 };
 
@@ -1446,7 +1446,6 @@ static void host_x86_cpu_class_init(ObjectClass *oc, void *data)
     cpu_x86_fill_model_id(host_cpudef.model_id);
 
     xcc->cpu_def = &host_cpudef;
-    host_cpudef.cache_info_passthrough = true;
 
     /* level, xlevel, xlevel2, and the feature words are initialized on
      * instance_init, because they require KVM to be initialized.
@@ -2094,7 +2093,6 @@ static void x86_cpu_load_def(X86CPU *cpu, X86CPUDefinition *def, Error **errp)
     object_property_set_int(OBJECT(cpu), def->stepping, "stepping", errp);
     object_property_set_int(OBJECT(cpu), def->xlevel, "xlevel", errp);
     object_property_set_int(OBJECT(cpu), def->xlevel2, "xlevel2", errp);
-    cpu->cache_info_passthrough = def->cache_info_passthrough;
     object_property_set_str(OBJECT(cpu), def->model_id, "model-id", errp);
     for (w = 0; w < FEATURE_WORDS; w++) {
         env->features[w] = def->features[w];