target-i386: kvm: Don't enable MONITOR by default on any CPU model

KVM never supported the MONITOR flag so it doesn't make sense to have it
enabled by default when KVM is enabled.

The rationale here is similar to the cases where it makes sense to have
a feature enabled by default on all CPU models when on KVM mode (e.g.
x2apic). In this case we are having a feature disabled by default for
the same reasons.

In this case we don't need machine-type compat code because it is
currently impossible to run a KVM VM with the MONITOR flag set.
Reviewed-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>
Signed-off-by: NAndreas Färber <afaerber@suse.de>

target-i386/cpu.c

@@ -373,6 +373,12 @@ static uint32_t kvm_default_features[FEATURE_WORDS] = {
     [FEAT_1_ECX] = CPUID_EXT_X2APIC,
 };
 
+/* Features that are not added by default to any CPU model when KVM is enabled.
+ */
+static uint32_t kvm_default_unset_features[FEATURE_WORDS] = {
+    [FEAT_1_ECX] = CPUID_EXT_MONITOR,
+};
+
 void x86_cpu_compat_disable_kvm_features(FeatureWord w, uint32_t features)
 {
     kvm_default_features[w] &= ~features;
@@ -1888,6 +1894,7 @@ static void x86_cpu_load_def(X86CPU *cpu, X86CPUDefinition *def, Error **errp)
         FeatureWord w;
         for (w = 0; w < FEATURE_WORDS; w++) {
             env->features[w] |= kvm_default_features[w];
+            env->features[w] &= ~kvm_default_unset_features[w];
         }
     }