Re: [Qemu-devel] [RFC 02/12] target-i386: Don't set any KVM flag by default if KVM is disabled

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Jan 09, 2013 at 04:53:42PM -0200, Eduardo Habkost wrote:
> This is a cleanup that tries to solve two small issues:
> 
>  - We don't need a separate kvm_pv_eoi_features variable just to keep a
>    constant calculated at compile-time, and this style would require
>    adding a separate variable (that's declared twice because of the
>    CONFIG_KVM ifdef) for each feature that's going to be enabled/disable
>    by machine-type compat code.
>  - The pc-1.3 code is setting the kvm_pv_eoi flag on cpuid_kvm_features
>    even when KVM is disabled at runtime. This small incosistency in
>    the cpuid_kvm_features field isn't a problem today because
>    cpuid_kvm_features is ignored by the TCG code, but it may cause
>    unexpected problems later when refactoring the CPUID handling code.
> 
> This patch eliminates the kvm_pv_eoi_features variable and simply uses
> kvm_enabled() inside the enable_kvm_pv_eoi() compat function, so it
> enables kvm_pv_eoi only if KVM is enabled. I believe this makes the
> behavior of enable_kvm_pv_eoi() clearer and easier to understand.
> 
> Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>

Acked-by: Michael S. Tsirkin <mst@redhat.com>



> ---
> Cc: kvm@vger.kernel.org
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Cc: Gleb Natapov <gleb@redhat.com>
> Cc: Marcelo Tosatti <mtosatti@redhat.com>
> 
> Changes v2:
>  - Coding style fix
> 
> Changes v3:
>  - Eliminate #ifdef by using the fake KVM_FEATURE_PV_EOI #define
> 
> Changes v4:
>  - Check kvm_enabled() when actually using kvm_default_features
>  - Eliminate Yet Another #ifdef by using the fake KVM_FEATURE_*
>    #defines on kvm_default_features initialization
> ---
>  target-i386/cpu.c | 16 ++++++----------
>  1 file changed, 6 insertions(+), 10 deletions(-)
> 
> diff --git a/target-i386/cpu.c b/target-i386/cpu.c
> index e4dc370..57a22b7 100644
> --- a/target-i386/cpu.c
> +++ b/target-i386/cpu.c
> @@ -206,22 +206,16 @@ typedef struct model_features_t {
>  int check_cpuid = 0;
>  int enforce_cpuid = 0;
>  
> -#if defined(CONFIG_KVM)
>  static uint32_t kvm_default_features = (1 << KVM_FEATURE_CLOCKSOURCE) |
>          (1 << KVM_FEATURE_NOP_IO_DELAY) |
>          (1 << KVM_FEATURE_CLOCKSOURCE2) |
>          (1 << KVM_FEATURE_ASYNC_PF) |
>          (1 << KVM_FEATURE_STEAL_TIME) |
>          (1 << KVM_FEATURE_CLOCKSOURCE_STABLE_BIT);
> -static const uint32_t kvm_pv_eoi_features = (0x1 << KVM_FEATURE_PV_EOI);
> -#else
> -static uint32_t kvm_default_features = 0;
> -static const uint32_t kvm_pv_eoi_features = 0;
> -#endif
>  
>  void enable_kvm_pv_eoi(void)
>  {
> -    kvm_default_features |= kvm_pv_eoi_features;
> +    kvm_default_features |= (1UL << KVM_FEATURE_PV_EOI);
>  }
>  
>  void host_cpuid(uint32_t function, uint32_t count,
> @@ -1343,13 +1337,15 @@ static int cpu_x86_parse_featurestr(x86_def_t *x86_cpu_def, char *features)
>      unsigned int i;
>      char *featurestr; /* Single 'key=value" string being parsed */
>      /* Features to be added */
> -    FeatureWordArray plus_features = {
> -        [FEAT_KVM] = kvm_default_features,
> -    };
> +    FeatureWordArray plus_features = { 0 };
>      /* Features to be removed */
>      FeatureWordArray minus_features = { 0 };
>      uint32_t numvalue;
>  
> +    if (kvm_enabled()) {
> +        plus_features[FEAT_KVM] = kvm_default_features;
> +    }
> +
>      add_flagname_to_bitmaps("hypervisor", plus_features);
>  
>      featurestr = features ? strtok(features, ",") : NULL;
> -- 
> 1.7.11.7