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Date:   Tue, 29 Oct 2019 16:13:02 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Luwei Kang <luwei.kang@intel.com>
Cc:     kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
        pbonzini@redhat.com, rkrcmar@redhat.com,
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        tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, hpa@zytor.com,
        x86@kernel.org, ak@linux.intel.com, thomas.lendacky@amd.com,
        acme@kernel.org, mark.rutland@arm.com,
        alexander.shishkin@linux.intel.com, jolsa@redhat.com,
        namhyung@kernel.org
Subject: Re: [PATCH v1 8/8] perf/x86: Add event owner check when PEBS output
 to Intel PT
Message-ID: <20191029151302.GO4097@hirez.programming.kicks-ass.net>
References: <1572217877-26484-1-git-send-email-luwei.kang@intel.com>
 <1572217877-26484-9-git-send-email-luwei.kang@intel.com>
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On Sun, Oct 27, 2019 at 07:11:17PM -0400, Luwei Kang wrote:
> For PEBS output to Intel PT, a Intel PT event should be the group
> leader of an PEBS counter event in host. For Intel PT
> virtualization enabling in KVM guest, the PT facilities will be
> passthrough to guest and do not allocate PT event from host perf
> event framework. This is different with PMU virtualization.
> 
> Intel new hardware feature that can make PEBS enabled in KVM guest
> by output PEBS records to Intel PT buffer. KVM need to allocate
> a event counter for this PEBS event without Intel PT event leader.
> 
> This patch add event owner check for PEBS output to PT event that
> only non-kernel event need group leader(PT).
> 
> Signed-off-by: Luwei Kang <luwei.kang@intel.com>
> ---
>  arch/x86/events/core.c     | 3 ++-
>  include/linux/perf_event.h | 1 +
>  kernel/events/core.c       | 2 +-
>  3 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
> index 7b21455..214041a 100644
> --- a/arch/x86/events/core.c
> +++ b/arch/x86/events/core.c
> @@ -1014,7 +1014,8 @@ static int collect_events(struct cpu_hw_events *cpuc, struct perf_event *leader,
>  		 * away, the group was broken down and this singleton event
>  		 * can't schedule any more.
>  		 */
> -		if (is_pebs_pt(leader) && !leader->aux_event)
> +		if (is_pebs_pt(leader) && !leader->aux_event &&
> +					!is_kernel_event(leader))

indent fail, but also, I'm not sure I buy this.

Surely pt-on-kvm has a perf event to claim PT for the vCPU context?

Even if not, this is not strictly correct. Not even now is KVM the sole
user of perf_event_create_kernel_counter(), so saying any kernel event
is excempt from this scheduling constraint is jsut wrong.

>  			return -EINVAL;
>  
>  		/*