From: Stephane Eranian eranian@google.com
[ Upstream commit bec49a9e05db3dbdca696fa07c62c52638fb6371 ]
When it is not possible for a non-privilege perf command to monitor at the kernel level (:k), the fallback code forces a :u. That works if the event was previously monitoring both levels. But if the event was already constrained to kernel only, then it does not make sense to restrict it to user only.
Given the code works by exclusion, a kernel only event would have:
attr->exclude_user = 1
The fallback code would add:
attr->exclude_kernel = 1
In the end the end would not monitor in either the user level or kernel level. In other words, it would count nothing.
An event programmed to monitor kernel only cannot be switched to user only without seriously warning the user.
This patch forces an error in this case to make it clear the request cannot really be satisfied.
Behavior with paranoid 1:
$ sudo bash -c "echo 1 > /proc/sys/kernel/perf_event_paranoid" $ perf stat -e cycles:k sleep 1
Performance counter stats for 'sleep 1':
1,520,413 cycles:k
1.002361664 seconds time elapsed
0.002480000 seconds user 0.000000000 seconds sys
Old behavior with paranoid 2:
$ sudo bash -c "echo 2 > /proc/sys/kernel/perf_event_paranoid" $ perf stat -e cycles:k sleep 1 Performance counter stats for 'sleep 1':
0 cycles:ku
1.002358127 seconds time elapsed
0.002384000 seconds user 0.000000000 seconds sys
New behavior with paranoid 2:
$ sudo bash -c "echo 2 > /proc/sys/kernel/perf_event_paranoid" $ perf stat -e cycles:k sleep 1 Error: You may not have permission to collect stats.
Consider tweaking /proc/sys/kernel/perf_event_paranoid, which controls use of the performance events system by unprivileged users (without CAP_PERFMON or CAP_SYS_ADMIN).
The current value is 2:
-1: Allow use of (almost) all events by all users Ignore mlock limit after perf_event_mlock_kb without CAP_IPC_LOCK
= 0: Disallow ftrace function tracepoint by users without CAP_PERFMON or CAP_SYS_ADMIN
Disallow raw tracepoint access by users without CAP_SYS_PERFMON or CAP_SYS_ADMIN
= 1: Disallow CPU event access by users without CAP_PERFMON or CAP_SYS_ADMIN = 2: Disallow kernel profiling by users without CAP_PERFMON or CAP_SYS_ADMIN
To make this setting permanent, edit /etc/sysctl.conf too, e.g.:
kernel.perf_event_paranoid = -1
v2 of this patch addresses the review feedback from jolsa@redhat.com.
Signed-off-by: Stephane Eranian eranian@google.com Reviewed-by: Ian Rogers irogers@google.com Acked-by: Jiri Olsa jolsa@redhat.com Tested-by: Arnaldo Carvalho de Melo acme@redhat.com Cc: Alexander Shishkin alexander.shishkin@linux.intel.com Cc: Jiri Olsa jolsa@redhat.com Cc: Mark Rutland mark.rutland@arm.com Cc: Namhyung Kim namhyung@kernel.org Cc: Peter Zijlstra peterz@infradead.org Link: http://lore.kernel.org/lkml/20200414161550.225588-1-irogers@google.com Signed-off-by: Arnaldo Carvalho de Melo acme@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- tools/perf/util/evsel.c | 4 ++++ 1 file changed, 4 insertions(+)
diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c index 68c5ab0e1800b..e8586957562b3 100644 --- a/tools/perf/util/evsel.c +++ b/tools/perf/util/evsel.c @@ -2796,6 +2796,10 @@ bool perf_evsel__fallback(struct perf_evsel *evsel, int err, char *new_name; const char *sep = ":";
+ /* If event has exclude user then don't exclude kernel. */ + if (evsel->core.attr.exclude_user) + return false; + /* Is there already the separator in the name. */ if (strchr(name, '/') || strchr(name, ':'))