linux-kernel - Re: [PATCH] coresight: trbe: Move check for kernelspace unmapped at EL0 to probe

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Date:   Thu, 3 Feb 2022 17:47:15 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Mike Leach <mike.leach@...aro.org>,
        Leo Yan <leo.yan@...aro.org>, coresight@...ts.linaro.org
Subject: Re: [PATCH] coresight: trbe: Move check for kernelspace unmapped at
 EL0 to probe



On 2/3/22 5:34 PM, Sudeep Holla wrote:
>> Could you please add a similar comment like SPE driver regarding how
>> the TRBE buffer will be inaccessible, if kernel gets unmapped at EL0
>> and trace capture will terminate.
>>
> Sure I can add that. But if the device probe fails, will you be able to even
> start the trace capture, sorry I didn't get what you mean by "trace capture
> will terminate". I assume it must be "trace capture is not possible or not
> allowed" IIUC.

I guess the comment should be framed like - what might happen if the following
code block which checks for arm64_kernel_unmapped_at_el0() is not present. If
TRBE gets enabled along with kernel unmapping at EL0 supported, trace capture
will terminate.