lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  PHC 
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date:   Sun, 17 Oct 2021 14:13:05 +0800
From:   Leo Yan <>
To:     German Gomez <>
Cc:     Will Deacon <>,,,
        John Garry <>,
        Mathieu Poirier <>,
        Mark Rutland <>,
        Alexander Shishkin <>,
        Jiri Olsa <>,
        Namhyung Kim <>,
        Mike Leach <>,,,
        James Clark <>
Subject: Re: [PATCH 4/5] perf arm-spe: Implement find_snapshot callback

Hi German, Will,

On Fri, Oct 15, 2021 at 01:33:39PM +0100, German Gomez wrote:


> $ ./perf record -vvv -e arm_spe/period=148576/u -S1000 -m16,16 -- taskset --cpu-list 0 stress --cpu 1 &

When testing Arm SPE snapshot mode with the command (it's quite
similiar with up command but not exactly same):

# ./perf --debug verbose=3 record -e arm_spe/period=148576/u -C 0 -S1000 -m16,16 \
    -- taskset --cpu-list 0 stress --cpu 1 &
# kill -USR2 [pid_num]

... then I wait for long time and didn't stop the perf program, then
I observed the output file contains many redundant events
PERF_RECORD_AUX.  E.g. in the shared perf data file [1], you could use
below commands to see tons of the events PERF_RECORD_AUX which I only
send only one USR2 signal for taking snapshot:

  # perf report -D -i --stdio | grep -E 'RECORD_AUX' | wc -l

  # perf report -D -i --stdio | grep -E 'SPE'
  . ... ARM SPE data: size 0x3e8 bytes
  Binary file (standard input) matches

I looked into the Arm SPE driver and found it doesn't really support
free run mode for AUX ring buffer when the driver runs in snapshot
mode, the pair functions perf_aux_output_end() and
perf_aux_output_begin() are invoked when every time handle the
interrupt.  The detailed flow is:

    `> arm_spe_pmu_buf_get_fault_act()
         `> arm_spe_perf_aux_output_end()
              `> set SPE registers
              `> perf_aux_output_end()
    `> arm_spe_perf_aux_output_begin()
         `> perf_aux_output_begin()
         `> set SPE registers

Seems to me, a possible solution is to add an extra parameter 'int
in_interrupt' for functions arm_spe_perf_aux_output_end() and
arm_spe_perf_aux_output_begin(), if this parameter is passed as 1 in
the interrupt handling, these two functions should skip invoking
perf_aux_output_end() and perf_aux_output_begin() so can avoid the
redundant perf event PERF_RECORD_AUX.

    `> arm_spe_pmu_buf_get_fault_act()
         `> arm_spe_perf_aux_output_end(..., in_interrupt=1)
              `> set SPE registers
    `> arm_spe_perf_aux_output_begin(..., in_interrupt=1)
         `> set SPE registers

P.s. I think Intel-PT has supported free run mode for snapshot mode,
so it should not generate interrupt in this mode.  Thus Intel-PT can
avoid this issue, please see the code [2].



Powered by blists - more mailing lists