linux-kernel - [PATCH 0/6] hw_breakpoint: Breakpoint modification fixes

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Date:   Mon, 27 Nov 2017 17:21:27 +0100
From:   Jiri Olsa <jolsa@...nel.org>
To:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        David Ahern <dsahern@...il.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Milind Chabbi <chabbi.milind@...il.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Hari Bathini <hbathini@...ux.vnet.ibm.com>,
        Jin Yao <yao.jin@...ux.intel.com>,
        Kan Liang <kan.liang@...el.com>,
        Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>,
        Oleg Nesterov <onestero@...hat.com>,
        Will Deacon <will.deacon@....com>
Subject: [PATCH 0/6] hw_breakpoint: Breakpoint modification fixes

hi,
Milind Chabbi introduced new ioctl interface to change
live breakpoint [1]. It allows to change its bp_addr,
bp_len and bp_type throught new ioctl for perf breakpoint
event.

We already have a kernel interface for this via 
modify_user_hw_breakpoint function. This function however
does not update the breakpoint slot counts.

So when the same functionality was exposed to user space
(Milind's change), with simple test program I could put wrong
slots count on arm server [2] and ended up with no breakpoints
available on the system. Note it's not an issue on x86, because
it shares slot single counter for both data and inst types
(CONFIG_HAVE_MIXED_BREAKPOINTS_REGS).

This patchset contains my fixes for keeping breakpoint slots
count updated. On top of it there's Milind's change for new
_IOC_MODIFY_ATTRIBUTES ioctl interface to change a breakpoint.

As I mentioned above there're kernel users of
modify_user_hw_breakpoint function, all ptrace related
AFAICS, which could got broken.. so cc-ing Oleg ;-)

I ran gdb and strace tests suites and got same amount of
skip/fail tests as when I run them on unpatched machine,
so I assume nothing new got broken.

It's also available in here:
  https://git.kernel.org/pub/scm/linux/kernel/git/jolsa/perf.git
  perf/bp

thanks,
jirka

[1] https://marc.info/?l=linux-kernel&m=151012255331565&w=2
[2] https://marc.info/?l=linux-man&m=151172469807302&w=2
---
Jiri Olsa (5):
      hw_breakpoint: Pass bp_type directly as find_slot_idx argument
      hw_breakpoint: Pass bp_type argument to __reserve_bp_slot|__release_bp_slot
      hw_breakpoint: Add modify_bp_slot function
      hw_breakpoint: Factor out __modify_user_hw_breakpoint function
      perf tests: Add breakpoint accounting/modify test

Milind Chabbi (1):
      perf/core: fast breakpoint modification via _IOC_MODIFY_ATTRIBUTES.

 include/linux/hw_breakpoint.h         |   6 ++++
 include/uapi/linux/perf_event.h       |   2 ++
 kernel/events/core.c                  |  47 ++++++++++++++++++++++++++++++
 kernel/events/hw_breakpoint.c         | 110 ++++++++++++++++++++++++++++++++++++++++++++++++---------------------
 tools/include/uapi/linux/perf_event.h |   2 ++
 tools/perf/tests/Build                |   1 +
 tools/perf/tests/bp_account.c         | 195 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 tools/perf/tests/builtin-test.c       |   4 +++
 tools/perf/tests/tests.h              |   1 +
 9 files changed, 335 insertions(+), 33 deletions(-)
 create mode 100644 tools/perf/tests/bp_account.c