From bec49a9e05db3dbdca696fa07c62c52638fb6371 Mon Sep 17 00:00:00 2001 From: Stephane Eranian Date: Tue, 14 Apr 2020 09:15:50 -0700 Subject: [PATCH] perf stat: Force error in fallback on :k events 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 Reviewed-by: Ian Rogers Acked-by: Jiri Olsa Tested-by: Arnaldo Carvalho de Melo Cc: Alexander Shishkin Cc: Jiri Olsa Cc: Mark Rutland Cc: Namhyung Kim Cc: Peter Zijlstra Link: http://lore.kernel.org/lkml/20200414161550.225588-1-irogers@google.com Signed-off-by: Arnaldo Carvalho de Melo --- 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 8300e8c7aea8..6a571d322bb2 100644 --- a/tools/perf/util/evsel.c +++ b/tools/perf/util/evsel.c @@ -2427,6 +2427,10 @@ bool perf_evsel__fallback(struct 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, ':'))