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

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Date:   Fri, 16 Oct 2020 14:10:47 +0530
From:   Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
To:     Leo Yan <leo.yan@...aro.org>
Cc:     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>,
        Suzuki K Poulose <suzuki.poulose@....com>
Subject: Re: [PATCH] coresight: etm4x: Add config to exclude kernel mode
 tracing

Hi Leo,

On 2020-10-16 12:54, Leo Yan wrote:
> On Thu, Oct 15, 2020 at 11:40:05PM -0700, Denis Nikitin wrote:
>> Hi Mathieu,
>> 
>> I think one of the use cases could be VMs.
>> Is there isolation between EL1 guest kernels which we can control from 
>> perf
>> in a system wide mode?
> 
> Sorry for suddenly jumping in.
> 
> For KVM, I think we need to implement mechanism for saving/restoring
> CoreSight context for every guest OS, the CPU PMUs has implemented
> related features [1].
> 
> Thanks,
> Leo
> 
> [1]
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm64/kvm/pmu.c
> 

What happens to the sysfs mode of tracing? For that we would still
need a config right to exclude kernel mode tracing completely.

Thanks,
Sai

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