Re: [Qemu-devel] [PATCH qom-cpu 2/7] target-i386: Don't set any KVM flag by default if KVM is disabled

[Igor Mammedov <imammedo@redhat.com>]

On Mon,  7 Jan 2013 16:20:43 -0200
Eduardo Habkost <ehabkost@redhat.com> 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.

Subj doesn't match what patch actually does.
Have you meant "Don't set kvm_pv_eoi flag by default if KVM is disabled"?
Although "eliminate kvm_pv_eoi_features variable" might better describe what
patch is doing.

> 
> Signed-off-by: Eduardo Habkost <ehabkost@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
> ---
>  target-i386/cpu.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/target-i386/cpu.c b/target-i386/cpu.c
> index 951e206..40400ac 100644
> --- a/target-i386/cpu.c
> +++ b/target-i386/cpu.c
> @@ -164,15 +164,15 @@ static uint32_t kvm_default_features = (1 <<
> KVM_FEATURE_CLOCKSOURCE) | (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;
> +    if (kvm_enabled()) {
> +        kvm_default_features |= (1UL << KVM_FEATURE_PV_EOI);
> +    }
>  }
>  
>  void host_cpuid(uint32_t function, uint32_t count,