3 files changed, 34 insertions, 0 deletions
diff --git a/include/hw/i386/pc.h b/include/hw/i386/pc.h
index f48d167207..d80859bfad 100644
--- a/include/hw/i386/pc.h
+++ b/include/hw/i386/pc.h
@@ -380,6 +380,11 @@ bool e820_get_entry(int, uint32_t, uint64_t *, uint64_t *);
 #define PC_COMPAT_2_8 \
     HW_COMPAT_2_8 \
     {\
+        .driver   = TYPE_X86_CPU,\
+        .property = "tcg-cpuid",\
+        .value    = "off",\
+    },\
+    {\
         .driver   = "kvmclock",\
         .property = "x-mach-use-reliable-get-clock",\
         .value    = "off",\
diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 4de91d5801..71983ef4e6 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -2632,12 +2632,15 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
     CPUState *cs = CPU(cpu);
     uint32_t pkg_offset;
     uint32_t limit;
+    uint32_t signature[3];
 
     /* Calculate & apply limits for different index ranges */
     if (index >= 0xC0000000) {
         limit = env->cpuid_xlevel2;
     } else if (index >= 0x80000000) {
         limit = env->cpuid_xlevel;
+    } else if (index >= 0x40000000) {
+        limit = 0x40000001;
     } else {
         limit = env->cpuid_level;
     }
@@ -2872,6 +2875,30 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
         }
         break;
     }
+    case 0x40000000:
+        /*
+         * CPUID code in kvm_arch_init_vcpu() ignores stuff
+         * set here, but we restrict to TCG none the less.
+         */
+        if (tcg_enabled() && cpu->expose_tcg) {
+            memcpy(signature, "TCGTCGTCGTCG", 12);
+            *eax = 0x40000001;
+            *ebx = signature[0];
+            *ecx = signature[1];
+            *edx = signature[2];
+        } else {
+            *eax = 0;
+            *ebx = 0;
+            *ecx = 0;
+            *edx = 0;
+        }
+        break;
+    case 0x40000001:
+        *eax = 0;
+        *ebx = 0;
+        *ecx = 0;
+        *edx = 0;
+        break;
     case 0x80000000:
         *eax = env->cpuid_xlevel;
         *ebx = env->cpuid_vendor1;
@@ -4018,6 +4045,7 @@ static Property x86_cpu_properties[] = {
     DEFINE_PROP_BOOL("kvm-no-smi-migration", X86CPU, kvm_no_smi_migration,
                      false),
     DEFINE_PROP_BOOL("vmware-cpuid-freq", X86CPU, vmware_cpuid_freq, true),
+    DEFINE_PROP_BOOL("tcg-cpuid", X86CPU, expose_tcg, true),
     DEFINE_PROP_END_OF_LIST()
 };
 
diff --git a/target/i386/cpu.h b/target/i386/cpu.h
index 7a228afd04..051867399b 100644
--- a/target/i386/cpu.h
+++ b/target/i386/cpu.h
@@ -1218,6 +1218,7 @@ struct X86CPU {
     bool check_cpuid;
     bool enforce_cpuid;
     bool expose_kvm;
+    bool expose_tcg;
     bool migratable;
     bool max_features; /* Enable all supported features automatically */
     uint32_t apic_id;