From: Arnaldo Carvalho de Melo <acme@redhat.com>

Date: Fri, 22 Sep 2017 15:41:44 -0300

Subject: perf evsel: Fix attr.exclude_kernel setting for default cycles:p

Git-commit: f1e52f14a69386ac460a8d700df0647a631cf595

Patch-mainline: v4.14-rc3

References: bsc#1083691

​

[suse: adjust context, skip failed fix d37a3697 ]

​

Yet another fix for probing the max attr.precise_ip setting: it is not

enough settting attr.exclude_kernel for !root users, as they _can_

profile the kernel if the kernel.perf_event_paranoid sysctl is set to

-1, so check that as well.

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Testing it:

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As non root:

​

  $ sysctl kernel.perf_event_paranoid

  kernel.perf_event_paranoid = 2

  $ perf record sleep 1

  $ perf evlist -v

  cycles:uppp: ..., exclude_kernel: 1, ... precise_ip: 3, ...

​

Now as non-root, but with kernel.perf_event_paranoid set set to the

most permissive value, -1:

​

  $ sysctl kernel.perf_event_paranoid

  kernel.perf_event_paranoid = -1

  $ perf record sleep 1

  $ perf evlist -v

  cycles:ppp: ..., exclude_kernel: 0, ... precise_ip: 3, ...

  $

​

I.e. non-root, default kernel.perf_event_paranoid: :uppp modifier = not allowed to sample the kernel,

     non-root, most permissible kernel.perf_event_paranoid: :ppp = allowed to sample the kernel.

​

In both cases, use the highest available precision: attr.precise_ip = 3.

​

Reported-and-Tested-by: Ingo Molnar <mingo@kernel.org>

Cc: Adrian Hunter <adrian.hunter@intel.com>

Cc: Andy Lutomirski <luto@kernel.org>

Cc: David Ahern <dsahern@gmail.com>

Cc: Jiri Olsa <jolsa@kernel.org>

Cc: Namhyung Kim <namhyung@kernel.org>

Cc: Wang Nan <wangnan0@huawei.com>

Fixes: d37a36979077 ("perf evsel: Fix attr.exclude_kernel setting for default cycles:p")

Link: http://lkml.kernel.org/n/tip-nj2qkf75xsd6pw6hhjzfqqdx@git.kernel.org

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

Signed-off-by: Tony Jones <tonyj@suse.de>

---

 tools/perf/util/evsel.c | 7 ++++++-

 1 file changed, 6 insertions(+), 1 deletion(-)

​

diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c

index 4bb89373eb52..0dccdb89572c 100644

--- a/tools/perf/util/evsel.c

+++ b/tools/perf/util/evsel.c

@@ -271,12 +271,17 @@ struct perf_evsel *perf_evsel__new_idx(struct perf_event_attr *attr, int idx)

    return evsel;

 }

+static bool perf_event_can_profile_kernel(void)

+{

+   return geteuid() == 0 || perf_event_paranoid() == -1;

+}

+

 struct perf_evsel *perf_evsel__new_cycles(bool precise)

 {

    struct perf_event_attr attr = {

        .type   = PERF_TYPE_HARDWARE,

        .config = PERF_COUNT_HW_CPU_CYCLES,

-       .exclude_kernel = 1,

+       .exclude_kernel = !perf_event_can_profile_kernel(),

    };

    struct perf_evsel *evsel;

​