The assumption in the cpu->max_features code is that anything
enabled on GET_SUPPORTED_CPUID should be enabled on "-cpu host".
This shouldn't be the case for FEAT_KVM_HINTS.

This adds a new FeatureWordInfo::no_autoenable_flags field, that
can be used to prevent FEAT_KVM_HINTS bits to be enabled
automatically.

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
---
 target/i386/cpu.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 1a6b082b6f..a20fe26573 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -295,6 +295,8 @@ typedef struct FeatureWordInfo {
     uint32_t tcg_features; /* Feature flags supported by TCG */
     uint32_t unmigratable_flags; /* Feature flags known to be unmigratable */
     uint32_t migratable_flags; /* Feature flags known to be migratable */
+    /* Features that shouldn't be auto-enabled by "-cpu host" */
+    uint32_t no_autoenable_flags;
 } FeatureWordInfo;
 
 static FeatureWordInfo feature_word_info[FEATURE_WORDS] = {
@@ -400,6 +402,11 @@ static FeatureWordInfo feature_word_info[FEATURE_WORDS] = {
         },
         .cpuid_eax = KVM_CPUID_FEATURES, .cpuid_reg = R_EDX,
         .tcg_features = TCG_KVM_FEATURES,
+        /*
+         * KVM hints aren't auto-enabled by -cpu host, they need to be
+         * explicitly enabled in the command-line.
+         */
+        .no_autoenable_flags = ~0U,
     },
     [FEAT_HYPERV_EAX] = {
         .feat_names = {
@@ -4062,7 +4069,8 @@ static void x86_cpu_expand_features(X86CPU *cpu, Error **errp)
              */
             env->features[w] |=
                 x86_cpu_get_supported_feature_word(w, cpu->migratable) &
-                ~env->user_features[w];
+                ~env->user_features[w] & \
+                ~feature_word_info[w].no_autoenable_flags;
         }
     }
 
-- 
2.14.3

2018-04-11 5:15 GMT+08:00 Eduardo Habkost <ehabkost@redhat.com>:
> The assumption in the cpu->max_features code is that anything
> enabled on GET_SUPPORTED_CPUID should be enabled on "-cpu host".
> This shouldn't be the case for FEAT_KVM_HINTS.
>
> This adds a new FeatureWordInfo::no_autoenable_flags field, that
> can be used to prevent FEAT_KVM_HINTS bits to be enabled
> automatically.
>
> Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>

Thanks for the patch, Eduardo!
Tested-by: Wanpeng Li <wanpengli@tencent.com>

Regards,
Wanpeng Li

> ---
>  target/i386/cpu.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> index 1a6b082b6f..a20fe26573 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -295,6 +295,8 @@ typedef struct FeatureWordInfo {
>      uint32_t tcg_features; /* Feature flags supported by TCG */
>      uint32_t unmigratable_flags; /* Feature flags known to be unmigratable */
>      uint32_t migratable_flags; /* Feature flags known to be migratable */
> +    /* Features that shouldn't be auto-enabled by "-cpu host" */
> +    uint32_t no_autoenable_flags;
>  } FeatureWordInfo;
>
>  static FeatureWordInfo feature_word_info[FEATURE_WORDS] = {
> @@ -400,6 +402,11 @@ static FeatureWordInfo feature_word_info[FEATURE_WORDS] = {
>          },
>          .cpuid_eax = KVM_CPUID_FEATURES, .cpuid_reg = R_EDX,
>          .tcg_features = TCG_KVM_FEATURES,
> +        /*
> +         * KVM hints aren't auto-enabled by -cpu host, they need to be
> +         * explicitly enabled in the command-line.
> +         */
> +        .no_autoenable_flags = ~0U,
>      },
>      [FEAT_HYPERV_EAX] = {
>          .feat_names = {
> @@ -4062,7 +4069,8 @@ static void x86_cpu_expand_features(X86CPU *cpu, Error **errp)
>               */
>              env->features[w] |=
>                  x86_cpu_get_supported_feature_word(w, cpu->migratable) &
> -                ~env->user_features[w];
> +                ~env->user_features[w] & \
> +                ~feature_word_info[w].no_autoenable_flags;
>          }
>      }
>
> --
> 2.14.3
>