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

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Message-ID: <20201016131407.GA31839@leoy-ThinkPad-X240s>
Date:   Fri, 16 Oct 2020 21:14:07 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     Suzuki Poulose <suzuki.poulose@....com>
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 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?

Obviously, this is a difficult task :)

Thanks,
Leo