linux-kernel - Re: [PATCH v2 1/5] KVM: x86: Add return value to kvm

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Date:   Thu, 17 Aug 2017 16:29:38 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Yu Zhang <yu.c.zhang@...ux.intel.com>, kvm@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, rkrcmar@...hat.com,
        tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
        xiaoguangrong@...cent.com, joro@...tes.org
Subject: Re: [PATCH v2 1/5] KVM: x86: Add return value to kvm_cpuid().

On 17/08/2017 15:20, Yu Zhang wrote:
>>
> 
> OK. And to return 0 for eax/ebx/ecx/edx if check_cpuid_limit() is also
> to be omitted,
> I'd better refactor this patch and move the "out:" before the if
> statement. :-)
> 
>                 best = check_cpuid_limit(vcpu, function, index);
>         }
> 
> +out:
>         if (best) {
>                 *eax = best->eax;
>                 *ebx = best->ebx;
> @@ -887,7 +888,6 @@ bool kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32
> *ebx,
>         } else
>                 *eax = *ebx = *ecx = *edx = 0;
> 
> -out:
>         trace_kvm_cpuid(function, *eax, *ebx, *ecx, *edx, entry_found);
>         return entry_found;
>  }
> 
> And for all get_cpuid() callers which is testing the existence of a
> feature, we do not need to
> check the return value, just checking the flag in the register should be
> fine, correct?

Yes, correct!

Paolo