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From:   Doug Anderson <dianders@chromium.org>
Date:   Mon, 1 Mar 2021 14:43:52 -0800
Message-ID: <CAD=FV=VJ-+c-8Bi+=YeTshgOBC64rzM4T-40qtybw7qZtt0vhA@mail.gmail.com>
Subject: Re: [PATCHv2 4/4] coresight: etm3x: Add support to exclude kernel
 mode tracing
To:     Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
Cc:     Mathieu Poirier <mathieu.poirier@linaro.org>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
        Mike Leach <mike.leach@linaro.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Leo Yan <leo.yan@linaro.org>, Jiri Olsa <jolsa@redhat.com>,
        Namhyung Kim <namhyung@kernel.org>, coresight@lists.linaro.org,
        Stephen Boyd <swboyd@chromium.org>,
        Denis Nikitin <denik@chromium.org>,
        Mattias Nissler <mnissler@chromium.org>,
        Al Grant <al.grant@arm.com>,
        linux-arm-msm <linux-arm-msm@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>
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Precedence: bulk

Hi,

On Mon, Mar 1, 2021 at 11:05 AM Sai Prakash Ranjan
<saiprakash.ranjan@codeaurora.org> wrote:
>
> On production systems with ETMs enabled, it is preferred to exclude
> kernel mode(NS EL1) tracing for security concerns and support only
> userspace(NS EL0) tracing. Perf subsystem interface uses the newly
> introduced kernel config CONFIG_EXCLUDE_KERNEL_PMU_TRACE to exclude
> kernel mode tracing, but there is an additional interface
> via sysfs for ETMs which also needs to be handled to exclude kernel
> mode tracing. So we use this same generic kernel config to handle
> the sysfs mode of tracing. This config is disabled by default and
> would not affect the current configuration which has both kernel and
> userspace tracing enabled by default.
>
> Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
> ---
>  drivers/hwtracing/coresight/coresight-etm3x-core.c  | 3 +++
>  drivers/hwtracing/coresight/coresight-etm3x-sysfs.c | 6 ++++++
>  2 files changed, 9 insertions(+)

Reviewed-by: Douglas Anderson <dianders@chromium.org>


> diff --git a/drivers/hwtracing/coresight/coresight-etm3x-sysfs.c b/drivers/hwtracing/coresight/coresight-etm3x-sysfs.c
> index e8c7649f123e..f522fc2e01b3 100644
> --- a/drivers/hwtracing/coresight/coresight-etm3x-sysfs.c
> +++ b/drivers/hwtracing/coresight/coresight-etm3x-sysfs.c
> @@ -116,6 +116,12 @@ static ssize_t mode_store(struct device *dev,
>         if (ret)
>                 return ret;
>
> +       if (IS_ENABLED(CONFIG_EXCLUDE_KERNEL_PMU_TRACE) && (!(val & ETM_MODE_EXCL_KERN))) {
> +               dev_warn(dev,
> +                       "Kernel mode tracing is not allowed, check your kernel config\n");

Same nit as in patch #3 that the above string should be indented by 1
more space.