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Subject: Re: [PATCH] KVM: x86/pmu: Add '.exclude_hv = 1' for guest perf_event
To:     Like Xu <like.xu@linux.intel.com>,
        Peter Zijlstra <peterz@infradead.org>
Cc:     Yao <yao.jin@linux.intel.com>,
        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>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20200812050722.25824-1-like.xu@linux.intel.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <5c41978e-8341-a179-b724-9aa6e7e8a073@redhat.com>
Date:   Wed, 12 Aug 2020 12:25:43 +0200
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On 12/08/20 07:07, Like Xu wrote:
> To emulate PMC counter for guest, KVM would create an
> event on the host with 'exclude_guest=0, exclude_hv=0'
> which simply makes no sense and is utterly broken.
> 
> To keep perf semantics consistent, any event created by
> pmc_reprogram_counter() should both set exclude_hv and
> exclude_host in the KVM context.
> 
> Message-ID: <20200811084548.GW3982@worktop.programming.kicks-ass.net>
> Signed-off-by: Like Xu <like.xu@linux.intel.com>
> ---
>  arch/x86/kvm/pmu.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
> index 67741d2a0308..6a30763a10d7 100644
> --- a/arch/x86/kvm/pmu.c
> +++ b/arch/x86/kvm/pmu.c
> @@ -108,6 +108,7 @@ static void pmc_reprogram_counter(struct kvm_pmc *pmc, u32 type,
>  		.exclude_host = 1,
>  		.exclude_user = exclude_user,
>  		.exclude_kernel = exclude_kernel,
> +		.exclude_hv = 1,
>  		.config = config,
>  	};
>  
> 

x86 does not have a hypervisor privilege level, so it never uses
exclude_hv; exclude_host already excludes all root mode activity for
both ring0 and ring3.

Paolo