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Date:   Mon, 18 May 2020 14:02:05 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Like Xu <like.xu@linux.intel.com>
Cc:     Paolo Bonzini <pbonzini@redhat.com>, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        Thomas Gleixner <tglx@linutronix.de>, ak@linux.intel.com,
        wei.w.wang@intel.com
Subject: Re: [PATCH v11 05/11] perf/x86: Keep LBR stack unchanged in host
 context for guest LBR event
Message-ID: <20200518120205.GF277222@hirez.programming.kicks-ass.net>
References: <20200514083054.62538-1-like.xu@linux.intel.com>
 <20200514083054.62538-6-like.xu@linux.intel.com>
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On Thu, May 14, 2020 at 04:30:48PM +0800, Like Xu wrote:
> @@ -544,7 +562,12 @@ void intel_pmu_lbr_enable_all(bool pmi)
>  {
>  	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
>  
> -	if (cpuc->lbr_users)
> +	/*
> +	 * When the LBR hardware is scheduled for a guest LBR event,
> +	 * the guest will dis/enables LBR itself at the appropriate time,
> +	 * including configuring MSR_LBR_SELECT.
> +	 */
> +	if (cpuc->lbr_users && !cpuc->guest_lbr_enabled)
>  		__intel_pmu_lbr_enable(pmi);
>  }

No!, that should be done through perf_event_attr::exclude_host, as I
believe all the other KVM event do it.