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Message-ID: <93e822b1-76d1-454b-a42f-adf9292d4da6@arm.com>
Date: Tue, 8 Oct 2024 07:52:17 +0100
From: Leo Yan <leo.yan@....com>
To: Leo Yan <leo.yan@...ux.dev>, Julien Meunier <julien.meunier@...ia.com>
Cc: Suzuki K Poulose <suzuki.poulose@....com>,
Mike Leach <mike.leach@...aro.org>, James Clark <james.clark@...aro.org>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
stable@...r.kernel.org, coresight@...ts.linaro.org,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] coresight: etm4x: Fix PID tracing when perf is run in an
init PID namespace
On 10/7/2024 9:05 PM, Leo Yan wrote:
>
> Hi Julien,
>
> On Wed, Sep 25, 2024 at 03:13:56PM +0200, Julien Meunier wrote:
>> The previous implementation limited the tracing capabilities when perf
>> was run in the init PID namespace, making it impossible to trace
>> applications in non-init PID namespaces.
>>
>> This update improves the tracing process by verifying the event owner.
>> This allows us to determine whether the user has the necessary
>> permissions to trace the application.
>
> The original commit aab473867fed is not for constraint permission. It is
> about PID namespace mismatching issue.
>
> E.g. Perf runs in non-root namespace, thus it records process info in the
> non-root PID namespace. On the other hand, Arm CoreSight traces PID for
> root namespace, as a result, it will lead mess when decoding.
>
> With this change, I am not convinced that Arm CoreSight can trace PID for
> non-root PID namespace. Seems to me, the concerned issue is still existed
> - it might cause PID mismatching issue between hardware trace data and
> Perf's process info.
I thought again and found I was wrong with above conclusion. This patch is a
good fixing for the perf running in root namespace to profile programs in
non-root namespace. Sorry for noise.
Maybe it is good to improve a bit comments to avoid confusion. See below.
[...]
>> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
>> index bf01f01964cf..8365307b1aec 100644
>> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
>> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
>> @@ -695,7 +695,7 @@ static int etm4_parse_event_config(struct coresight_device *csdev,
>>
>> /* Only trace contextID when runs in root PID namespace */
We can claim the requirement for the *tool* running in root PID namespae.
/* Only trace contextID when the tool runs in root PID namespace */
>> if ((attr->config & BIT(ETM_OPT_CTXTID)) &&
>> - task_is_in_init_pid_ns(current))
>> + task_is_in_init_pid_ns(event->owner))
>> /* bit[6], Context ID tracing bit */
>> config->cfg |= TRCCONFIGR_CID;
>>
>> @@ -710,7 +710,7 @@ static int etm4_parse_event_config(struct coresight_device *csdev,
>> goto out;
>> }
>> /* Only trace virtual contextID when runs in root PID namespace */
Ditto.
/* Only trace virtual contextID when the tool runs in root PID namespace */
With above change:
Reviewed-by: Leo Yan <leo.yan@....com>
>> - if (task_is_in_init_pid_ns(current))
>> + if (task_is_in_init_pid_ns(event->owner))
>> config->cfg |= TRCCONFIGR_VMID | TRCCONFIGR_VMIDOPT;
>> }
>>
>> --
>> 2.34.1
>>
>>
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