[PATCH v4 0/3] Fix vDSO clock_getres()

[Vincenzo Frascino]

clock_getres in the vDSO library has to preserve the same behaviour
of posix_get_hrtimer_res().

In particular, posix_get_hrtimer_res() does:
    sec = 0;
    ns = hrtimer_resolution;
and hrtimer_resolution depends on the enablement of the high
resolution timers that can happen either at compile or at run time.

A possible fix is to change the vdso implementation of clock_getres,
keeping a copy of hrtimer_resolution in vdso data and using that
directly [1].

This patchset implements the proposed fix for arm64, powerpc, s390,
nds32 and adds a test to verify that the syscall and the vdso library
implementation of clock_getres return the same values.

Even if these patches are unified by the same topic, there is no
dependency between them, hence they can be merged singularly by each
arch maintainer.

Note: arm64 and nds32 respective fixes have been merged in 5.2-rc1,
hence they have been removed from this series.

[1] https://marc.info/?l=linux-arm-kernel&m=155110381930196&w=2

Changes:
--------
v4:
  - Address review comments.
v3:
  - Rebased on 5.2-rc1.
  - Address review comments.
v2:
  - Rebased on 5.1-rc5.
  - Addressed review comments.

Cc: Christophe Leroy <christophe.leroy at c-s.fr>
Cc: Benjamin Herrenschmidt <benh at kernel.crashing.org>
Cc: Paul Mackerras <paulus at samba.org>
Cc: Michael Ellerman <mpe at ellerman.id.au>
Cc: Martin Schwidefsky <schwidefsky at de.ibm.com>
Cc: Heiko Carstens <heiko.carstens at de.ibm.com>
Cc: Shuah Khan <shuah at kernel.org>
Cc: Thomas Gleixner <tglx at linutronix.de>
Cc: Arnd Bergmann <arnd at arndb.de>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino at arm.com>

Vincenzo Frascino (3):
  powerpc: Fix vDSO clock_getres()
  s390: Fix vDSO clock_getres()
  kselftest: Extend vDSO selftest to clock_getres

 arch/powerpc/include/asm/vdso_datapage.h      |   2 +
 arch/powerpc/kernel/asm-offsets.c             |   2 +-
 arch/powerpc/kernel/time.c                    |   1 +
 arch/powerpc/kernel/vdso32/gettimeofday.S     |   7 +-
 arch/powerpc/kernel/vdso64/gettimeofday.S     |   7 +-
 arch/s390/include/asm/vdso.h                  |   1 +
 arch/s390/kernel/asm-offsets.c                |   2 +-
 arch/s390/kernel/time.c                       |   1 +
 arch/s390/kernel/vdso32/clock_getres.S        |  12 +-
 arch/s390/kernel/vdso64/clock_getres.S        |  10 +-
 tools/testing/selftests/vDSO/Makefile         |   2 +
 .../selftests/vDSO/vdso_clock_getres.c        | 124 ++++++++++++++++++
 12 files changed, 155 insertions(+), 16 deletions(-)
 create mode 100644 tools/testing/selftests/vDSO/vdso_clock_getres.c

-- 
2.21.0