linux-kernel - Re: [PATCH] coresight: etm4x: Add config to exclude kernel mode tracing

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Date:   Fri, 16 Oct 2020 14:17:51 +0100
From:   Suzuki Poulose <suzuki.poulose@....com>
To:     Leo Yan <leo.yan@...aro.org>
Cc:     Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>,
        Denis Nikitin <denik@...omium.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        linux-arm-msm@...r.kernel.org, coresight@...ts.linaro.org,
        linux-kernel@...r.kernel.org, Stephen Boyd <swboyd@...omium.org>,
        linux-arm-kernel@...ts.infradead.org,
        Mike Leach <mike.leach@...aro.org>
Subject: Re: [PATCH] coresight: etm4x: Add config to exclude kernel mode
 tracing

On 10/16/20 2:14 PM, Leo Yan wrote:
> On Fri, Oct 16, 2020 at 12:38:47PM +0100, Suzuki Kuruppassery Poulose wrote:
> 
> [...]
> 
>>>> What happens to the sysfs mode of tracing? For that we would still
>>>> need a config right to exclude kernel mode tracing completely.
>>>
>>> IIUC, sysfs mode and perf mode both can apply the same approach, the
>>> guest OS runs a thread context for the host, so when a guest OS is
>>> switched in or out, the hypervisor can save/restore the context for
>>> the guest OS; thus every guest OS will have its dedicated context and
>>> trace data ideally.
>>
>> I don't think Guest Context is something we can support as mentioned
>> above, at least for systems without sysreg access for ETMs (and virtualizing
>> ETRs is a different story !)
> 
> Thanks for sharing thoughts, Suzuki.
> 
> I missed the device virtulisation.  Here should virtualize all devices
> (includes CoreSight ETM/funnel/ETR/ETF)?  Or only need to virtualize
> ETRs?

I wouldn't even think of virtualizing the components without sysreg
access. So let us not worry about it :-)

Cheers
Suzuki