linux-kernel - Re: [PATCH 6/7] perf cs-etm: Don't hard code config attribute when configuring the event

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Message-ID: <20251204144336.GN724103@e132581.arm.com>
Date: Thu, 4 Dec 2025 14:43:36 +0000
From: Leo Yan <leo.yan@....com>
To: James Clark <james.clark@...aro.org>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Mike Leach <mike.leach@...aro.org>,
	John Garry <john.g.garry@...cle.com>, Will Deacon <will@...nel.org>,
	Leo Yan <leo.yan@...ux.dev>, linux-perf-users@...r.kernel.org,
	linux-kernel@...r.kernel.org, coresight@...ts.linaro.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 6/7] perf cs-etm: Don't hard code config attribute when
 configuring the event

On Thu, Dec 04, 2025 at 02:08:59PM +0000, James Clark wrote:

[...]

> > > +	err = evsel__get_config_val(cs_etm_pmu, evsel, "contextid", &ctxt);
> > > +	if (err)
> > > +		return err;
> > > +	err = evsel__get_config_val(cs_etm_pmu, evsel, "contextid1", &ctxt1);
> > > +	if (err)
> > > +		return err;
> > > +	err = evsel__get_config_val(cs_etm_pmu, evsel, "contextid2", &ctxt2);
> > > +	if (err)
> > > +		return err;
> > 
> > Seems to me, this is not right.  The current code checks any context
> > ID setting but it can tolerate if missing "contexid[*]" format.
> > 
> > After calling evsel__get_config_val(), if any "contextid[*]" format is
> > missed, it returns error and will diretly bail out.  As a result,
> > cs_etm_validate_context_id() will always return error.
> > 
> 
> Missed by the driver or the user? evsel__get_config_val() only returns an
> error when "contextid" isn't published by the driver, not when the user
> doesn't supply one of those options. The actual user supplied value is in
> the out param, not the return value.

My question is for missing format from user.  Thanks for reminding the
error is only for driver's publishing.

> Having said that, this does make it an error if the driver did stop
> publishing one, which might be too inflexible and is a new behavior. I can
> change to it ignore the errors instead.

Yeah, this will likely break nVHE / pKVM cases.

Thanks,
Leo