linux-kernel - Re: [PATCH 10/61] KVM: x86: Clean up CPUID 0x7 sub-leaf loop

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Message-ID: <87ftf4rpi2.fsf@vitty.brq.redhat.com>
Date:   Fri, 21 Feb 2020 15:20:21 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 10/61] KVM: x86: Clean up CPUID 0x7 sub-leaf loop

Sean Christopherson <sean.j.christopherson@...el.com> writes:

> Refactor the sub-leaf loop for CPUID 0x7 to move the main leaf out of
> said loop.  The emitted code savings is basically a mirage, as the
> handling of the main leaf can easily be split to its own helper to avoid
> code bloat.
>
> No functional change intended.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> ---
>  arch/x86/kvm/cpuid.c | 18 +++++++++---------
>  1 file changed, 9 insertions(+), 9 deletions(-)
>
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 6e1685a16cca..b626893a11d5 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -573,16 +573,16 @@ static inline int __do_cpuid_func(struct kvm_cpuid_entry2 *entry, u32 function,
>  	case 7: {
>  		int i;
>  
> -		for (i = 0; ; ) {
> +		do_cpuid_7_mask(entry, 0);
> +
> +		for (i = 1; i <= entry->eax; i++) {
> +			if (*nent >= maxnent)
> +				goto out;
> +
> +			do_host_cpuid(&entry[i], function, i);
> +			++*nent;
> +
>  			do_cpuid_7_mask(&entry[i], i);
> -			if (i == entry->eax)
> -				break;
> -			if (*nent >= maxnent)
> -				goto out;
> -
> -			++i;
> -			do_host_cpuid(&entry[i], function, i);
> -			++*nent;
>  		}
>  		break;
>  	}

Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>

-- 
Vitaly