linux-kernel - Re: [PATCH v2 1/3] KVM: x86: X86_FEATURE

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Date:   Mon, 7 Aug 2017 10:29:19 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Radim Krčmář <rkrcmar@...hat.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v2 1/3] KVM: x86: X86_FEATURE_NRIPS is not scattered
 anymore

On 05.08.2017 00:12, Radim Krčmář wrote:
> bit(X86_FEATURE_NRIPS) is 3 since 2ccd71f1b278 ("x86/cpufeature: Move
> some of the scattered feature bits to x86_capability"), so we can
> simplify the code.
> 
> Signed-off-by: Radim Krčmář <rkrcmar@...hat.com>
> ---
> v2: new, explain why it's ok to use X86_FEATURE_NRIPS (David)
> ---
>  arch/x86/kvm/cpuid.h | 14 +-------------
>  1 file changed, 1 insertion(+), 13 deletions(-)
> 
> diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
> index da6728383052..c723d64657d0 100644
> --- a/arch/x86/kvm/cpuid.h
> +++ b/arch/x86/kvm/cpuid.h
> @@ -160,25 +160,13 @@ static inline bool guest_cpuid_has_rdtscp(struct kvm_vcpu *vcpu)
>  	return best && (best->edx & bit(X86_FEATURE_RDTSCP));
>  }
>  
> -/*
> - * NRIPS is provided through cpuidfn 0x8000000a.edx bit 3
> - */
> -#define BIT_NRIPS	3
> -
>  static inline bool guest_cpuid_has_nrips(struct kvm_vcpu *vcpu)
>  {
>  	struct kvm_cpuid_entry2 *best;
>  
>  	best = kvm_find_cpuid_entry(vcpu, 0x8000000a, 0);
> -
> -	/*
> -	 * NRIPS is a scattered cpuid feature, so we can't use
> -	 * X86_FEATURE_NRIPS here (X86_FEATURE_NRIPS would be bit
> -	 * position 8, not 3).
> -	 */
> -	return best && (best->edx & bit(BIT_NRIPS));
> +	return best && (best->edx & bit(X86_FEATURE_NRIPS));
>  }
> -#undef BIT_NRIPS
>  
>  static inline int guest_cpuid_family(struct kvm_vcpu *vcpu)
>  {
> 

Reviewed-by: David Hildenbrand <david@...hat.com>

-- 

Thanks,

David