Re: [PATCH v4 08/10] Documentation: admin-guide: Add riscv sysctl_perf_user_access

[Atish Patra <atishp@atishpatra.org>]

On Mon, Jul 3, 2023 at 5:54 AM 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)
> -=================================
> +perf_user_access (arm64 and riscv only)
> +=======================================
> +
> +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
> +=====
>
>  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 only.
I don't think there is any way to access the counters directly in ARM64.

>  See Documentation/arm64/perf.rst for more information.
>
> +riscv
> +=====
> +
> +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 to cycle
> +and insret CSRs only). Note that this legacy value is deprecated and will be
> +removed once all user space applications are fixed.
> +
> +Note that the time CSR is always directly accessible to all modes.
>
>  pid_max
>  =======
> --
> 2.39.2
>


-- 
Regards,
Atish

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