linux-kernel - Re: [PATCH 3/7] perf: arm64: Use rseq to test userspace access to pmu counters

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Message-ID: <ff5897eb-ae6c-482f-148b-947a661fde4f@arm.com>
Date:   Tue, 25 Jun 2019 14:29:56 +0100
From:   Raphael Gault <raphael.gault@....com>
To:     Mark Rutland <mark.rutland@....com>, will.deacon@....com
Cc:     Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        mingo@...hat.com, peterz@...radead.org, catalin.marinas@....com,
        mathieu.desnoyers@...icios.com
Subject: Re: [PATCH 3/7] perf: arm64: Use rseq to test userspace access to pmu
 counters

Hi Mark, Hi Will,

Now that we have a better idea what enabling this feature for 
heterogeneous systems would look like (both with or without using 
rseqs), it might be worth discussing if this is in fact a desirable 
thing in term of performance-complexity trade off.

Indeed, while not as scary as first thought, maybe the rseq method would 
still dissuade users from using this feature. It is also worth noting 
that if we only enable this feature on homogeneous system, the `mrs` 
hook/emulation would not be necessary.
If because of the complexity of the setup we need to consider whether we 
want to upstream this and have to maintain it afterward.

Thanks,

-- 
Raphael Gault