linux-kernel - [PATCH v4 08/10] Documentation: admin-guide: Add riscv sysctl_perf_user

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Message-Id: <20230727141428.962286-9-alexghiti@rivosinc.com>
Date:   Thu, 27 Jul 2023 16:14:26 +0200
From:   Alexandre Ghiti <alexghiti@...osinc.com>
To:     Jonathan Corbet <corbet@....net>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Atish Patra <atishp@...shpatra.org>,
        Anup Patel <anup@...infault.org>,
        Will Deacon <will@...nel.org>, Rob Herring <robh@...nel.org>,
        Andrew Jones <ajones@...tanamicro.com>,
        Rémi Denis-Courmont <remi@...lab.net>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-perf-users@...r.kernel.org, linux-riscv@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org
Cc:     Alexandre Ghiti <alexghiti@...osinc.com>
Subject: [PATCH v4 08/10] Documentation: admin-guide: Add riscv sysctl_perf_user_access

riscv now uses this sysctl so document its usage for this architecture.

Signed-off-by: Alexandre Ghiti <alexghiti@...osinc.com>
Reviewed-by: Andrew Jones <ajones@...tanamicro.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 3800fab1619b..8019103aac10 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.
+
 See Documentation/arch/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