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Peter Anvin" , "Rafael J. Wysocki" , Pavel Machek , Greg Kroah-Hartman , Danilo Krummrich , Johan Hovold , Sebastian Andrzej Siewior , Mathieu Desnoyers , Jiayuan Chen , "Steven Rostedt (Google)" , "Vineeth Pillai (Google)" , Frederic Weisbecker , Andi Kleen , linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, driver-core@lists.linux.dev Subject: Re: [PATCH 2/6] perf/x86/intel/pt: Stop tracing if VMXON has not yet happened Message-ID: <20261102095750.GS1779021@noisy.programming.kicks-ass.net> References: <20261102074039.26983-1-adrian.hunter@intel.com> <20261102074039.26983-3-adrian.hunter@intel.com> X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261102074039.26983-3-adrian.hunter@intel.com> On Mon, Nov 02, 2026 at 09:40:35AM +0200, Adrian Hunter wrote: > arch/x86/events/intel/pt.c | 16 +++++++++++++++- > 1 file changed, 15 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/events/intel/pt.c b/arch/x86/events/intel/pt.c > index 49349afee611..36bf039668d7 100644 > --- a/arch/x86/events/intel/pt.c > +++ b/arch/x86/events/intel/pt.c > @@ -567,6 +567,15 @@ static void pt_config(struct perf_event *event) > pt_config_enable(event); > } > > +static bool pt_trace_enabled(void) > +{ > + u64 ctl; > + > + rdmsrq(MSR_IA32_RTIT_CTL, ctl); > + > + return ctl & RTIT_CTL_TRACEEN; > +} > + > static void pt_config_stop(struct perf_event *event) > { > struct pt *pt = this_cpu_ptr(&pt_ctx); > @@ -577,7 +586,12 @@ static void pt_config_stop(struct perf_event *event) > return; > > ctl &= ~RTIT_CTL_TRACEEN; > - if (!READ_ONCE(pt->vmx_on)) > + /* > + * vmx_on is set before VMXON, so tracing may not have stopped yet. > + * RTIT_CTL can be written until VMXON, and after VMXON TraceEn is > + * clear, so still write RTIT_CTL if TraceEn is set. > + */ > + if (!READ_ONCE(pt->vmx_on) || pt_trace_enabled()) > wrmsrq(MSR_IA32_RTIT_CTL, ctl); > > WRITE_ONCE(event->hw.aux_config, ctl); It seems rather unfortunate to issue a RDMSR for state we fully control. Surely we can track this?