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From:   Atish Patra <atishp@atishpatra.org>
Date:   Fri, 14 Jul 2023 01:50:59 -0700
Message-ID: <CAOnJCUJGHWicrhGOGPK_aduaD9jXz7THHcbU+i+7tK-ChtQxNg@mail.gmail.com>
Subject: Re: [PATCH v4 08/10] Documentation: admin-guide: Add riscv sysctl_perf_user_access
To:     Alexandre Ghiti <alexghiti@rivosinc.com>
Cc:     Jonathan Corbet <corbet@lwn.net>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@kernel.org>,
        Namhyung Kim <namhyung@kernel.org>,
        Ian Rogers <irogers@google.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Anup Patel <anup@brainfault.org>,
        Will Deacon <will@kernel.org>, Rob Herring <robh@kernel.org>,
        Andrew Jones <ajones@ventanamicro.com>,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-perf-users@vger.kernel.org, linux-riscv@lists.infradead.org,
        linux-arm-kernel@lists.infradead.org
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On Mon, Jul 3, 2023 at 5:54=E2=80=AFAM Alexandre Ghiti <alexghiti@rivosinc.=
com> wrote:
>
> riscv now uses this sysctl so document its usage for this architecture.
>
> Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
> ---
>  Documentation/admin-guide/sysctl/kernel.rst | 27 ++++++++++++++++++---
>  1 file changed, 23 insertions(+), 4 deletions(-)
>
> diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/=
admin-guide/sysctl/kernel.rst
> index d85d90f5d000..19b627883313 100644
> --- a/Documentation/admin-guide/sysctl/kernel.rst
> +++ b/Documentation/admin-guide/sysctl/kernel.rst
> @@ -941,16 +941,35 @@ enabled, otherwise writing to this file will return=
 ``-EBUSY``.
>  The default value is 8.
>
>
> -perf_user_access (arm64 only)
> -=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D
> +perf_user_access (arm64 and riscv only)
> +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> +
> +Controls user space access for reading perf event counters.
>
> -Controls user space access for reading perf event counters. When set to =
1,
> -user space can read performance monitor counter registers directly.
> +arm64
> +=3D=3D=3D=3D=3D
>
>  The default value is 0 (access disabled).
>
> +When set to 1, user space can read performance monitor counter registers
> +directly.
> +

For ARM64, 1 also enables reading performance counters via perf interface o=
nly.
I don't think there is any way to access the counters directly in ARM64.

>  See Documentation/arm64/perf.rst for more information.
>
> +riscv
> +=3D=3D=3D=3D=3D
> +
> +When set to 0, user space access is disabled.
> +
> +The default value is 1, user space can read performance monitor counter
> +registers through perf, any direct access without perf intervention will=
 trigger
> +an illegal instruction.
> +
> +When set to 2, which enables legacy mode (user space has direct access t=
o cycle
> +and insret CSRs only). Note that this legacy value is deprecated and wil=
l be
> +removed once all user space applications are fixed.
> +
> +Note that the time CSR is always directly accessible to all modes.
>
>  pid_max
>  =3D=3D=3D=3D=3D=3D=3D
> --
> 2.39.2
>


--=20
Regards,
Atish