[RFC PATCH 2/2] target/i386: Add "-cpu +kvm-no-defaults"

[David Edmondson]

From: Joao Martins <joao.m.martins@oracle.com>

When enabling reporting to the guest that the hypervisor is KVM via
"+kvm", we also enable all of the known KVM features that are
supported by the host kernel. A new "kvm-no-defaults" option for -cpu
defeats this, enabling KVM reporting but *not* enabling any specific
KVM features. Those features can be enabled one-by-one using existing
feature flags, such as kvmclock, kvm-pv-eoi, etc.

Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: David Edmondson <david.edmondson@oracle.com>
---
 target/i386/cpu.c | 5 +++++
 target/i386/cpu.h | 3 +++
 2 files changed, 8 insertions(+)

diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 13f58ef183..4f1e807815 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -6398,6 +6398,10 @@ static void x86_cpu_expand_features(X86CPU *cpu, Error 
**errp)
     int i;
     GList *l;
 
+    if (kvm_enabled() && cpu->kvm_no_defaults) {
+        env->features[FEAT_KVM] = 0;
+    }
+
     for (l = plus_features; l; l = l->next) {
         const char *prop = l->data;
         if (!object_property_set_bool(OBJECT(cpu), prop, true, errp)) {
@@ -7269,6 +7273,7 @@ static Property x86_cpu_properties[] = {
     DEFINE_PROP_BOOL("cpuid-0xb", X86CPU, enable_cpuid_0xb, true),
     DEFINE_PROP_BOOL("lmce", X86CPU, enable_lmce, false),
     DEFINE_PROP_BOOL("l3-cache", X86CPU, enable_l3_cache, true),
+    DEFINE_PROP_BOOL("kvm-no-defaults", X86CPU, kvm_no_defaults, false),
     DEFINE_PROP_BOOL("kvm-no-smi-migration", X86CPU, kvm_no_smi_migration,
                      false),
     DEFINE_PROP_BOOL("vmware-cpuid-freq", X86CPU, vmware_cpuid_freq, true),
diff --git a/target/i386/cpu.h b/target/i386/cpu.h
index d23a5b340a..f76af4a771 100644
--- a/target/i386/cpu.h
+++ b/target/i386/cpu.h
@@ -1744,6 +1744,9 @@ struct X86CPU {
     /* if set, limit maximum value for phys_bits when host_phys_bits is true */
     uint8_t host_phys_bits_limit;
 
+    /* Don't automatically enable all of the discovered KVM features. */
+    bool kvm_no_defaults;
+
     /* Stop SMI delivery for migration compatibility with old machines */
     bool kvm_no_smi_migration;
 
-- 
2.29.2