Re: [PATCH v3 0/2] perf tests: Check for ARM [vectors] page

[Florian Fainelli <f.fainelli@gmail.com>]

Le 12/27/18 à 2:55 AM, Namhyung Kim a écrit :
> Hello,
> 
> On Thu, Dec 20, 2018 at 07:43:35PM -0800, Florian Fainelli wrote:
>> Hi all,
>>
>> I just painfully learned that perf would segfault when
>> CONFIG_KUSER_HELPERS is disabled because it unconditionally makes use of
> 
> Could you please elaborate?

Sure, I was debugging why perf was segfaulting on my systems and saw
that the faulting address was within 0xffff_0000 (high vectors); and
because CONFIG_KUSER_HELPERS was not enabled, nothing was mapped at that
address so this was a legitimate crash. This was on a variety of ARMv7A
systems, Cortex-A9, Cortex-A5 etc.

Later on, I found that in tools/arch/arm/include/asm/barrier.h the
barriers are unconditionally defined to make use of the [vectors] page
that the ARM kernel only sets up when CONFIG_KUSER_HELPERS is enabled
and this is the reason for the crash.

Testing for the page itself is pretty harmless if you think we should
make something more robust around checking for HAVE_AUXTRACE_SUPPORT
(which appears to be the specific location making use of barriers), let
me know.

Thanks!

> 
> Thanks,
> Namhyung
> 
> 
>> it. This patch series adds an ARM test for that by leveraging the
>> existing find_vdso_map() function and making it more generic and capable
>> of location any map within /proc/self/maps.
>>
>> Changes in v3:
>>
>> - remove find_vdso_map() call find_map() with VDSO__MAP_NAME
>>
>> Changes in v2:
>>
>> - use strlen() instead of sizeof() -1 since we made the page name a
>>   parameter
>> - use TEST_OK/TEST_FAIL in lieu of 0/-1
>> - added an error message indicating CONFIG_KUSER_HELPERS might be
>>   disabled
>>
>> Florian Fainelli (2):
>>   perf tools: Make find_vdso_map() more modular
>>   perf tests: Add a test for the ARM 32-bit [vectors] page
>>
>>  tools/perf/Makefile.perf                      |  4 ++--
>>  tools/perf/arch/arm/tests/Build               |  1 +
>>  tools/perf/arch/arm/tests/arch-tests.c        |  4 ++++
>>  tools/perf/arch/arm/tests/vectors-page.c      | 24 +++++++++++++++++++
>>  tools/perf/perf-read-vdso.c                   |  6 ++---
>>  tools/perf/tests/tests.h                      |  5 ++++
>>  .../perf/util/{find-vdso-map.c => find-map.c} |  7 +++---
>>  tools/perf/util/vdso.c                        |  6 ++---
>>  8 files changed, 45 insertions(+), 12 deletions(-)
>>  create mode 100644 tools/perf/arch/arm/tests/vectors-page.c
>>  rename tools/perf/util/{find-vdso-map.c => find-map.c} (71%)
>>
>> -- 
>> 2.17.1
>>


-- 
Florian