On Fri, 1 Feb 2019 10:29:11 +0300 Alexey Budankov <alexey.budankov@xxxxxxxxxxxxxxx> wrote: > Extend perf-security.rst file with perf_events/Perf resource control > section describing RLIMIT_NOFILE and perf_event_mlock_kb settings for > performance monitoring user processes. > > Signed-off-by: Alexey Budankov <alexey.budankov@xxxxxxxxxxxxxxx> Overall these patches seem reasonable, though I have some nits to pick. I'm happy to apply them but wouldn't mind an ack from the perf camp. Alexey, could you wrap your paragraphs at 72-75 columns? > --- > Documentation/admin-guide/perf-security.rst | 36 +++++++++++++++++++++ > 1 file changed, 36 insertions(+) > > diff --git a/Documentation/admin-guide/perf-security.rst b/Documentation/admin-guide/perf-security.rst > index f73ebfe9bfe2..ff6832191577 100644 > --- a/Documentation/admin-guide/perf-security.rst > +++ b/Documentation/admin-guide/perf-security.rst > @@ -84,6 +84,40 @@ governed by perf_event_paranoid [2]_ setting: > locking limit is imposed but ignored for unprivileged processes with > CAP_IPC_LOCK capability. > > +perf_events/Perf resource control > +--------------------------------- > + > +perf_events system call API [2]_ allocates file descriptors for every configured *The* perf_events system call API > +PMU event. Open file descriptors are a per-process accountable *resource* governed > +by RLIMIT_NOFILE [11]_ limit (ulimit -n), which is usually derived from the login by *the* RLIMIT_NOFILE > +shell process. When configuring Perf collection for a long list of events on a > +large server system, this limit can be easily hit preventing required monitoring > +configuration. RLIMIT_NOFILE limit can be increased on per-user basis modifying > +content of limits.conf file [12]_ on some systems. Ordinary Perf sampling session of *the* limits.conf file Ordinarily, a Perf > +(perf record) requires an amount of open perf_event file descriptors that is not > +less than a number of monitored events multiplied by a number of monitored CPUs. > + > +An amount of memory available to user processes for capturing performance monitoring > +data is governed by perf_event_mlock_kb [2]_ setting. This perf_event specific by *the* perf_event_mlock_kb > +*resource* setting defines overall per-cpu limits of memory allowed for mapping Why the *emphasis* here? > +by the user processes to execute performance monitoring. The setting essentially > +extends RLIMIT_MEMLOCK [11]_ limit but only for memory regions mapped specially extends *the* RMLIMIT_MEMLOCK limit *,* but only > +for capturing monitored performance events and related data. > + > +For example, if a machine has eight cores and perf_event_mlock_kb limit is set > +to 516 KiB then a user process is provided with 516 KiB * 8 = 4128 KiB of memory Kib, then > +above RLIMIT_MEMLOCK limit (ulimit -l) for perf_event mmap buffers. In particular above *the* RLIMIT_MEMLOCK particular, > +this means that if the user wants to start two or more performance monitoring that, if > +processes, it is required to manually distribute available 4128 KiB between the s/it is/they are/ > +monitoring processes, for example, using --mmap-pages Perf record mode option. using *the* --mmap-pages option > +Otherwise, the first started performance monitoring process allocates all available > +4128 KiB and the other processes will fail to proceed due to the lack of memory. > + > +RLIMIT_MEMLOCK and perf_event_mlock_kb *resource* constraints are ignored for > +processes with CAP_IPC_LOCK capability. Thus, perf_events/Perf privileged users with *the* CAP_IPC_LOCK > +can be provided with memory above the constraints for perf_events/Perf performance > +monitoring purpose by providing the Perf executable with CAP_IPC_LOCK capability. > + > Bibliography > ------------ > > @@ -94,4 +128,6 @@ Bibliography > .. [5] `<https://www.kernel.org/doc/html/latest/security/credentials.html>`_ > .. [6] `<http://man7.org/linux/man-pages/man7/capabilities.7.html>`_ > .. [7] `<http://man7.org/linux/man-pages/man2/ptrace.2.html>`_ > +.. [11] `<http://man7.org/linux/man-pages/man2/getrlimit.2.html>`_ > +.. [12] `<http://man7.org/linux/man-pages/man5/limits.conf.5.html>`_ Thanks, jon
