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* [PATCH v4 0/3] cpufreq/amd-pstate: Fix null pointer dereference when frequency invariance is disabled
@ 2023-05-17 16:28 Wyes Karny
  2023-05-17 16:28 ` [PATCH v4 1/3] amd_pstate: Add ->fast_switch() callback Wyes Karny
                   ` (2 more replies)
  0 siblings, 3 replies; 11+ messages in thread
From: Wyes Karny @ 2023-05-17 16:28 UTC (permalink / raw)
  To: ray.huang, rafael, viresh.kumar
  Cc: linux-pm, linux-kernel, gautham.shenoy, Wyes Karny

Currently, amd_pstate only uses `adjust_perf` and `target` callback
functions to get the frequency/effective utilization data from scaling
governors. But the governor can switch back to fast_switch (as
fast_switch_possible is set) when frequency invariance is disabled. In
that case, if the driver didn't set fast_switch function pointer, null
pointer dereference can happen and the kernel will crash.

Currently, frequency invariance is turned off when any anomaly is
detected with aperf/mperf readings. Which triggers this problem.

Fix this by adding `fast_switch` function in the amd_pstate driver.

The same problem could arise with any scaling driver which doesn't set
fast_switch but sets fast_switch_possible.  Return failure while loading
such drivers.

Changelog:
v3 -> v4:
- Add extra patch to remove fast_switch_possible flag from amd_pstate
  active mode driver.
- Fail to load such drivers which sets fast_switch_possible flag but not
  fast_switch.

v2 -> v3
- Add fast_switch callback in amd_pstate and warn if any driver
  sets fast_swich_possible flag but not fast_switch function pointer.

v1 -> v2
- Remove fast_switch_enabled flag dependency for adjust_perf callback

v1: https://lore.kernel.org/linux-pm/20230410095045.14872-1-wyes.karny@amd.com/
v2: https://lore.kernel.org/linux-pm/20230509180503.739208-1-wyes.karny@amd.com/
v3: https://lore.kernel.org/lkml/20230515113404.4259-1-wyes.karny@amd.com/

Gautham R. Shenoy (1):
  amd_pstate: Add ->fast_switch() callback

Wyes Karny (2):
  cpufreq/amd-pstate: Remove fast_switch_possible flag from active
    driver
  cpufreq: Return failure if fast_switch is not set and
    fast_switch_possible is set

 drivers/cpufreq/amd-pstate.c | 38 ++++++++++++++++++++++++++++--------
 drivers/cpufreq/cpufreq.c    |  5 +++++
 include/linux/cpufreq.h      |  4 +++-
 3 files changed, 38 insertions(+), 9 deletions(-)

-- 
2.34.1


^ permalink raw reply	[flat|nested] 11+ messages in thread

end of thread, other threads:[~2023-06-15 16:16 UTC | newest]

Thread overview: 11+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2023-05-17 16:28 [PATCH v4 0/3] cpufreq/amd-pstate: Fix null pointer dereference when frequency invariance is disabled Wyes Karny
2023-05-17 16:28 ` [PATCH v4 1/3] amd_pstate: Add ->fast_switch() callback Wyes Karny
2023-05-24 17:47   ` Rafael J. Wysocki
2023-05-29  6:57     ` Wyes Karny
2023-05-17 16:28 ` [PATCH v4 2/3] cpufreq/amd-pstate: Remove fast_switch_possible flag from active driver Wyes Karny
2023-05-17 16:28 ` [PATCH v4 3/3] cpufreq: Return failure if fast_switch is not set and fast_switch_possible is set Wyes Karny
2023-05-22  8:28   ` kernel test robot
2023-05-24 17:44   ` Rafael J. Wysocki
2023-05-29 14:08     ` Wyes Karny
2023-05-29 14:25       ` [PATCH v4.1] cpufreq: Fail driver register if it has adjust_perf without fast_switch Wyes Karny
2023-06-15 16:16         ` Rafael J. Wysocki

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