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Subject: Re: [PATCH] coresight: etm4x: Add config to exclude kernel mode
 tracing
To:     Leo Yan <leo.yan@linaro.org>
Cc:     Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>,
        Denis Nikitin <denik@chromium.org>,
        Mathieu Poirier <mathieu.poirier@linaro.org>,
        linux-arm-msm@vger.kernel.org, coresight@lists.linaro.org,
        linux-kernel@vger.kernel.org, Stephen Boyd <swboyd@chromium.org>,
        linux-arm-kernel@lists.infradead.org,
        Mike Leach <mike.leach@linaro.org>
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 <20201016092450.GG4646@leoy-ThinkPad-X240s>
 <f6ee4156-664c-7bff-8e35-5cd1acdbaa84@arm.com>
 <20201016131407.GA31839@leoy-ThinkPad-X240s>
From:   Suzuki Poulose <suzuki.poulose@arm.com>
Message-ID: <16b3be3a-0d2d-0d0f-24a5-020480ed980c@arm.com>
Date:   Fri, 16 Oct 2020 14:17:51 +0100
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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