linux-kernel - Re: [KVM x86 vPMU Patch 2/2] KVM: x86/vPMU: Fix unnecessary signed extension for AMD PERFCTRn

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Date:	Tue, 11 Aug 2015 09:33:18 +0200
From:	Andrew Jones <drjones@...hat.com>
To:	Wei Huang <wei@...hat.com>
Cc:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	pbonzini@...hat.com, gleb@...nel.org, tglx@...utronix.de,
	mingo@...hat.com, hpa@...or.com, x86@...nel.org, joro@...tes.org,
	trivial@...nel.org
Subject: Re: [KVM x86 vPMU Patch 2/2] KVM: x86/vPMU: Fix unnecessary signed
 extension for AMD PERFCTRn

On Fri, Aug 07, 2015 at 03:53:30PM -0400, Wei Huang wrote:
> According to AMD programmer's manual, AMD PERFCTRn is 64-bit MSR which,
> unlike Intel perf counters, doesn't require signed extension. This
> patch removes the unnecessary conversion in SVM vPMU code when PERFCTRn
> is being updated.
> 
> Signed-off-by: Wei Huang <wei@...hat.com>
> ---
>  arch/x86/kvm/pmu_amd.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/pmu_amd.c b/arch/x86/kvm/pmu_amd.c
> index 886aa25..39b9112 100644
> --- a/arch/x86/kvm/pmu_amd.c
> +++ b/arch/x86/kvm/pmu_amd.c
> @@ -133,8 +133,6 @@ static int amd_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  	/* MSR_K7_PERFCTRn */
>  	pmc = get_gp_pmc(pmu, msr, MSR_K7_PERFCTR0);
>  	if (pmc) {
> -		if (!msr_info->host_initiated)
> -			data = (s64)data;
>  		pmc->counter += data - pmc_read_counter(pmc);
>  		return 0;
>  	}
> -- 
> 1.8.3.1

Reviewed-by: Andrew Jones <drjones@...hat.com>
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