linux-kernel - Re: [PATCH v7 0/9] arm64 userspace counter access support

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Date:   Mon, 3 May 2021 09:56:37 -0500
From:   Rob Herring <robh@...nel.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Jiri Olsa <jolsa@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Honnappa Nagarahalli <honnappa.nagarahalli@....com>,
        Zachary.Leaf@....com, Raphael Gault <raphael.gault@....com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Itaru Kitayama <itaru.kitayama@...il.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v7 0/9] arm64 userspace counter access support

On Fri, Apr 30, 2021 at 1:59 PM Arnaldo Carvalho de Melo
<acme@...nel.org> wrote:
>
> Em Mon, Apr 19, 2021 at 10:15:02PM -0500, Rob Herring escreveu:
> > Hi all,
> >
> > Another version of arm64 userspace counter access support. I sent out
> > the libperf bits separately and those are now applied (Thanks!), so this
> > is just the arm64 bits.
> >
> >
> > This originally resurrected Raphael's series[1] to enable userspace counter
> > access on arm64. My previous versions are here[2][3][4][5][6][7]. A git
> > branch is here[8].
>
> Rob, please don't mix kernel patches with tools patches. The kernel
> bits, if arch specific should go via the arch maintainer, core stuff to
> PeterZ/Ingo/bpetkov/tglx, and tooling stuff I'll collect.

Okay, perhaps MAINTAINERS should be updated to reflect that better.

>
> We did it on purpose to avoid any semblance of kernel/tool lockstep.
>
> The kernel changes should not prevent the tooling from working and the
> tooling changes shouldn't require the kernel changes.
>
> Preexisting kernels should work with new tools and vice versa.

The only issue I see here is the userspace access tests will fail if
enabled in libperf for an arch but run on an older kernel without
userspace access support. I could instead skip tests if cap_user_rdpmc
is not set, but then how to test that it is set when it should be? I
suppose checking sysfs 'rdpmc' is one option assuming we end up with
the same file on Arm.

Rob