Re: [Qemu-devel] [PATCH for-2.12] i386: Don't automatically enable FEAT_KVM_HINTS bits

[Wanpeng Li]

2018-04-11 5:15 GMT+08:00 Eduardo Habkost <address@hidden>:
> 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 <address@hidden>
> Signed-off-by: Eduardo Habkost <address@hidden>

Thanks for the patch, Eduardo!
Tested-by: Wanpeng Li <address@hidden>

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
>