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From:   Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>
Date:   Tue, 7 Apr 2020 14:02:51 -0300
To:     Alexey Budankov <alexey.budankov@linux.intel.com>
Cc:     Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Ingo Molnar <mingo@redhat.com>,
        James Morris <jmorris@namei.org>,
        Namhyung Kim <namhyung@kernel.org>,
        Serge Hallyn <serge@hallyn.com>, Jiri Olsa <jolsa@redhat.com>,
        Song Liu <songliubraving@fb.com>,
        Andi Kleen <ak@linux.intel.com>,
        Stephane Eranian <eranian@google.com>,
        Igor Lubashev <ilubashe@akamai.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        "linux-security-module@vger.kernel.org" 
        <linux-security-module@vger.kernel.org>,
        "selinux@vger.kernel.org" <selinux@vger.kernel.org>,
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        "linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
        linux-man@vger.kernel.org
Subject: Re: [PATCH v8 00/12] Introduce CAP_PERFMON to secure system
 performance monitoring and observability
Message-ID: <20200407170251.GE12003@kernel.org>
References: <f96f8f8a-e65c-3f36-dc85-fc3f5191e8c5@linux.intel.com>
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 <10cc74ee-8587-8cdb-f85f-5724b370a2ce@linux.intel.com>
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Em Tue, Apr 07, 2020 at 07:52:56PM +0300, Alexey Budankov escreveu:
> 
> On 07.04.2020 19:36, Arnaldo Carvalho de Melo wrote:
> > Em Tue, Apr 07, 2020 at 05:54:27PM +0300, Alexey Budankov escreveu:
> >> Could makes sense adding cap_ipc_lock to the binary to isolate from this:

> >> kernel/events/core.c: 6101
> >> 	if ((locked > lock_limit) && perf_is_paranoid() &&
> >> 		!capable(CAP_IPC_LOCK)) {
> >> 		ret = -EPERM;
> >> 		goto unlock;
> >> 	}

> > That did the trick, I'll update the documentation and include in my
> > "Committer testing" section:
 
> Looks like top mode somehow reaches perf mmap limit described here [1].
> Using -m option solves the issue avoiding cap_ipc_lock on my 8 cores machine:
> perf top -e cycles -m 1

So this would read better?

diff --git a/Documentation/admin-guide/perf-security.rst b/Documentation/admin-guide/perf-security.rst
index ed33682e26b0..d44dd24b0244 100644
--- a/Documentation/admin-guide/perf-security.rst
+++ b/Documentation/admin-guide/perf-security.rst
@@ -127,8 +127,8 @@ taken to create such groups of privileged Perf users.
 
 ::
 
-   # setcap "cap_perfmon,cap_ipc_lock,cap_sys_ptrace,cap_syslog=ep" perf
-   # setcap -v "cap_perfmon,cap_ipc_lock,cap_sys_ptrace,cap_syslog=ep" perf
+   # setcap "cap_perfmon,cap_sys_ptrace,cap_syslog=ep" perf
+   # setcap -v "cap_perfmon,cap_sys_ptrace,cap_syslog=ep" perf
    perf: OK
    # getcap perf
    perf = cap_sys_ptrace,cap_syslog,cap_perfmon+ep
@@ -140,6 +140,10 @@ i.e.:
 
    # setcap "38,cap_ipc_lock,cap_sys_ptrace,cap_syslog=ep" perf
 
+Note that you may need to have 'cap_ipc_lock' in the mix for tools such as
+'perf top', alternatively use 'perf top -m N', to reduce the memory that
+it uses for the perf ring buffer, see the memory allocation section below.
+
 As a result, members of perf_users group are capable of conducting
 performance monitoring and observability by using functionality of the
 configured Perf tool executable that, when executes, passes perf_events