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Stephane Eranian c8317e9fc4 perf stat: Force error in fallback on :k events 
[ Upstream commit bec49a9e05 ]

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>
 		2020-10-01 13:17:55 +02:00
Documentation affs: fix basic permission bits to actually work 2020-09-09 19:12:34 +02:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
arch KVM: Remove CREATE_IRQCHIP/SET_PIT2 race 2020-10-01 13:17:55 +02:00
block block: only call sched requeue_request() for scheduled requests 2020-09-23 12:40:37 +02:00
certs PKCS#7: Refactor verify_pkcs7_signature() 2019-08-05 18:40:18 -04:00
crypto crypto: af_alg - Work around empty control messages without MSG_MORE 2020-09-03 11:27:05 +02:00
drivers serial: uartps: Wait for tx_empty in console setup 2020-10-01 13:17:55 +02:00
fs btrfs: fix setting last_trans for reloc roots 2020-10-01 13:17:55 +02:00
include ALSA: hda: Skip controller resume if not needed 2020-10-01 13:17:54 +02:00
init exec: Add exec_update_mutex to replace cred_guard_mutex 2020-10-01 13:17:47 +02:00
ipc ipc/util.c: sysvipc_find_ipc() incorrectly updates position index 2020-05-20 08:20:16 +02:00
kernel workqueue: Remove the warning in wq_worker_sleeping() 2020-10-01 13:17:54 +02:00
lib kernel/sysctl-test: Add null pointer test for sysctl.c:proc_dointvec() 2020-10-01 13:17:10 +02:00
mm mm/mmap.c: initialize align_offset explicitly for vm_unmapped_area 2020-10-01 13:17:54 +02:00
net SUNRPC: Don't start a timer on an already queued rpc task 2020-10-01 13:17:53 +02:00
samples bpf: Fix fds_example SIGSEGV error 2020-08-19 08:16:03 +02:00
scripts checkpatch: fix the usage of capture group ( ... ) 2020-09-09 19:12:37 +02:00
security selinux: sel_avc_get_stat_idx should increase position index 2020-10-01 13:17:32 +02:00
sound ALSA: hda: Skip controller resume if not needed 2020-10-01 13:17:54 +02:00
tools perf stat: Force error in fallback on :k events 2020-10-01 13:17:55 +02:00
usr initramfs: restore default compression behavior 2020-04-08 09:08:38 +02:00
virt KVM: fix overflow of zero page refcount with ksm running 2020-10-01 13:17:31 +02:00
.clang-format clang-format: Update with the latest for_each macro list 2019-08-31 10:00:51 +02:00
.cocciconfig
…
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Modules updates for v5.4 2019-09-22 10:34:46 -07:00
.mailmap ARM: SoC fixes 2019-11-10 13:41:59 -08:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS MAINTAINERS: Remove Simon as Renesas SoC Co-Maintainer 2019-10-10 08:12:51 -07:00
Kbuild kbuild: do not descend to ./Kbuild when cleaning 2019-08-21 21:03:58 +09:00
Kconfig docs: kbuild: convert docs to ReST and rename to *.rst 2019-06-14 14:21:21 -06:00
MAINTAINERS Documentation/llvm: add documentation on building w/ Clang/LLVM 2020-08-26 10:40:46 +02:00
Makefile Linux 5.4.68 2020-09-26 18:03:16 +02:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.