[PATCH] tools/perf: doc: Add permission and sysctl notice

From: Masami Hiramatsu
Date: Wed May 26 2021 - 05:01:29 EST


Add a section to notify the permission and sysctl setting
for perf probe. And fix some indentations.

Reported-by: Ravi Bangoria <ravi.bangoria@xxxxxxxxxxxxx>
Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
---
tools/perf/Documentation/perf-probe.txt | 17 ++++++++++++++---
1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/tools/perf/Documentation/perf-probe.txt b/tools/perf/Documentation/perf-probe.txt
index ed3ecfa422e1..38f60ac58a8e 100644
--- a/tools/perf/Documentation/perf-probe.txt
+++ b/tools/perf/Documentation/perf-probe.txt
@@ -226,7 +226,7 @@ So, "source.c:100-120" shows lines between 100th to l20th in source.c file. And

LAZY MATCHING
-------------
- The lazy line matching is similar to glob matching but ignoring spaces in both of pattern and target. So this accepts wildcards('*', '?') and character classes(e.g. [a-z], [!A-Z]).
+The lazy line matching is similar to glob matching but ignoring spaces in both of pattern and target. So this accepts wildcards('*', '?') and character classes(e.g. [a-z], [!A-Z]).

e.g.
'a=*' can matches 'a=b', 'a = b', 'a == b' and so on.
@@ -235,8 +235,8 @@ This provides some sort of flexibility and robustness to probe point definitions

FILTER PATTERN
--------------
- The filter pattern is a glob matching pattern(s) to filter variables.
- In addition, you can use "!" for specifying filter-out rule. You also can give several rules combined with "&" or "|", and fold those rules as one rule by using "(" ")".
+The filter pattern is a glob matching pattern(s) to filter variables.
+In addition, you can use "!" for specifying filter-out rule. You also can give several rules combined with "&" or "|", and fold those rules as one rule by using "(" ")".

e.g.
With --filter "foo* | bar*", perf probe -V shows variables which start with "foo" or "bar".
@@ -295,6 +295,17 @@ Add a probe in a source file using special characters by backslash escape
./perf probe -x /opt/test/a.out 'foo\+bar.c:4'


+PERMISSIONS AND SYSCTL
+----------------------
+Since perf probe depends on ftrace (tracefs) and kallsyms (/proc/kallsyms), you have to care about the permission and some sysctl knobs.
+
+ - Since tracefs and kallsyms requires root or privileged user to access it, the following perf probe commands also require it; --add, --del, --list (except for --cache option)
+
+ - /proc/sys/kernel/kptr_restrict = 2 (restrict all users) also prevents perf probe to retrieve the important information from kallsyms. You also need to set to 1 (restrict non CAP_SYSLOG users) for the above commands.
+
+ - Since the perf probe commands read the vmlinux and/or the debuginfo file, you need to ensure that you can read those files.
+
+
SEE ALSO
--------
linkperf:perf-trace[1], linkperf:perf-record[1], linkperf:perf-buildid-cache[1]