linux-kernel - Re: [RFC PATCH v2 2/3] perf/x86/intel/pt: Introduce and export pt_get_curr

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Date:   Mon, 26 Sep 2022 11:48:36 -0400
From:   "Liang, Kan" <kan.liang@...ux.intel.com>
To:     "Wang, Wei W" <wei.w.wang@...el.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     "Li, Xiaoyao" <xiaoyao.li@...el.com>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        "linux-perf-users@...r.kernel.org" <linux-perf-users@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: Re: [RFC PATCH v2 2/3] perf/x86/intel/pt: Introduce and export
 pt_get_curr_event()



On 2022-09-22 10:42 a.m., Wang, Wei W wrote:
> On Thursday, September 22, 2022 10:10 PM, Peter Zijlstra wrote:
>> On Thu, Sep 22, 2022 at 01:59:53PM +0000, Wang, Wei W wrote:
>>> On Thursday, September 22, 2022 9:35 PM, Peter Zijlstra
>>>> On Thu, Sep 22, 2022 at 12:58:49PM +0000, Wang, Wei W wrote:
>>>>
>>>>> Add a function to expose the current running PT event to users.
>>>>> One usage is in KVM, it needs to get and disable the running host
>>>>> PT event before VMEnter to the guest and resumes the event after
>> VMexit to host.
>>>>
>>>> You cannot just kill a host event like that. If there is a host
>>>> event, the guest looses out.
>>>
>>> OK. The intention was to pause the event (that only profiles host
>>> info) when switching to guest, and resume when switching back to host.
>>
>> If the even doesn't profile guest context, then yes. If it does profile guest
>> context, you can't.
> 
> Seems better to add this one:

If the guest host mode is enabled, I think the PT driver should not
allow the perf tool to create a host event with !exclude_guest.

Thanks,
Kan
> 
> +int perf_event_disable_local_exclude_guest(struct perf_event *event)
> +{
> +       struct perf_event_attr *attr = &event->attr;
> +
> +       if (!attr->exclude_guest)
> +               return -EPERM;
> +
> +       event_function_local(event, __perf_event_disable, NULL);
> +
> +       return 0;
> +}
> +EXPORT_SYMBOL_GPL(perf_event_disable_local_exclude_guest);
>