linux-kernel - Re: [PATCH 2/3] perf/x86/intel/pt: Inject PMI for KVM guest

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Date:   Thu, 7 Feb 2019 09:42:03 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Luwei Kang <luwei.kang@...el.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, hpa@...or.com, x86@...nel.org, songliubraving@...com,
        rkrcmar@...hat.com, zsm@...omium.org,
        alexander.shishkin@...ux.intel.com, konrad.wilk@...cle.com,
        ak@...ux.intel.com
Subject: Re: [PATCH 2/3] perf/x86/intel/pt: Inject PMI for KVM guest

On 06/02/19 17:34, Peter Zijlstra wrote:
> 
> How about we extend perf_guest_info_callback with an arch section and
> add:
> 
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 5aeb4c74fb99..76ce804e72c1 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -5835,6 +5835,9 @@ struct perf_guest_info_callbacks *perf_guest_cbs;
>  
>  int perf_register_guest_info_callbacks(struct perf_guest_info_callbacks *cbs)
>  {
> +	if (WARN_ON_ONCE(perf_guest_cbs))
> +		return -EBUSY;
> +
>  	perf_guest_cbs = cbs;
>  	return 0;
>  }
> @@ -5842,6 +5845,9 @@ EXPORT_SYMBOL_GPL(perf_register_guest_info_callbacks);
>  
>  int perf_unregister_guest_info_callbacks(struct perf_guest_info_callbacks *cbs)
>  {
> +	if (WARN_ON_ONCE(perf_guest_cbs != cbs))
> +		return -EINVAL;
> +
>  	perf_guest_cbs = NULL;
>  	return 0;
>  }

Makes total sense.

Paolo