kvm: Enable -cpu option to hide KVM

The latest Nvidia driver (337.88) specifically checks for KVM as the
hypervisor and reports Code 43 for the driver in a Windows guest when
found.  Removing or changing the KVM signature is sufficient for the
driver to load and work.  This patch adds an option to easily allow
the KVM hypervisor signature to be hidden using '-cpu kvm=off'.  We
continue to expose KVM via the cpuid value by default.  The state of
this option does not supercede or replace -enable-kvm or the accel=kvm
machine option.  This only changes the visibility of KVM to the guest
and paravirtual features specifically tied to the KVM cpuid.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

3 files changed, 17 insertions, 13 deletions

diff --git a/target-i386/cpu-qom.h b/target-i386/cpu-qom.h
index e9b3d577b3..0808cfc67d 100644
--- a/target-i386/cpu-qom.h
+++ b/target-i386/cpu-qom.h
@@ -87,6 +87,7 @@ typedef struct X86CPU {
     bool hyperv_time;
     bool check_cpuid;
     bool enforce_cpuid;
+    bool expose_kvm;
 
     /* if true the CPUID code directly forward host cache leaves to the guest */
     bool cache_info_passthrough;
diff --git a/target-i386/cpu.c b/target-i386/cpu.c
index 042a48d703..cbf1d979cb 100644
--- a/target-i386/cpu.c
+++ b/target-i386/cpu.c
@@ -2792,6 +2792,7 @@ static Property x86_cpu_properties[] = {
     DEFINE_PROP_BOOL("hv-time", X86CPU, hyperv_time, false),
     DEFINE_PROP_BOOL("check", X86CPU, check_cpuid, false),
     DEFINE_PROP_BOOL("enforce", X86CPU, enforce_cpuid, false),
+    DEFINE_PROP_BOOL("kvm", X86CPU, expose_kvm, true),
     DEFINE_PROP_END_OF_LIST()
 };
 
diff --git a/target-i386/kvm.c b/target-i386/kvm.c
index 3931d4c340..40cd4b84af 100644
--- a/target-i386/kvm.c
+++ b/target-i386/kvm.c
@@ -528,23 +528,25 @@ int kvm_arch_init_vcpu(CPUState *cs)
         has_msr_hv_hypercall = true;
     }
 
-    memcpy(signature, "KVMKVMKVM\0\0\0", 12);
-    c = &cpuid_data.entries[cpuid_i++];
-    c->function = KVM_CPUID_SIGNATURE | kvm_base;
-    c->eax = 0;
-    c->ebx = signature[0];
-    c->ecx = signature[1];
-    c->edx = signature[2];
+    if (cpu->expose_kvm) {
+        memcpy(signature, "KVMKVMKVM\0\0\0", 12);
+        c = &cpuid_data.entries[cpuid_i++];
+        c->function = KVM_CPUID_SIGNATURE | kvm_base;
+        c->eax = 0;
+        c->ebx = signature[0];
+        c->ecx = signature[1];
+        c->edx = signature[2];
 
-    c = &cpuid_data.entries[cpuid_i++];
-    c->function = KVM_CPUID_FEATURES | kvm_base;
-    c->eax = env->features[FEAT_KVM];
+        c = &cpuid_data.entries[cpuid_i++];
+        c->function = KVM_CPUID_FEATURES | kvm_base;
+        c->eax = env->features[FEAT_KVM];
 
-    has_msr_async_pf_en = c->eax & (1 << KVM_FEATURE_ASYNC_PF);
+        has_msr_async_pf_en = c->eax & (1 << KVM_FEATURE_ASYNC_PF);
 
-    has_msr_pv_eoi_en = c->eax & (1 << KVM_FEATURE_PV_EOI);
+        has_msr_pv_eoi_en = c->eax & (1 << KVM_FEATURE_PV_EOI);
 
-    has_msr_kvm_steal_time = c->eax & (1 << KVM_FEATURE_STEAL_TIME);
+        has_msr_kvm_steal_time = c->eax & (1 << KVM_FEATURE_STEAL_TIME);
+    }
 
     cpu_x86_cpuid(env, 0, 0, &limit, &unused, &unused, &unused);