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

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Message-ID: <Yyxke/IO+AP4EWwT@hirez.programming.kicks-ass.net>
Date:   Thu, 22 Sep 2022 15:34:51 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Wang, Wei W" <wei.w.wang@...el.com>
Cc:     "Liang, Kan" <kan.liang@...ux.intel.com>,
        "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 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.