[X][PATCH 0/2] LP#1822821 TSC clocksource not available in nested guests

[Heitor R. Alves de Siqueira]

BugLink: https://bugs.launchpad.net/bugs/1822821

[Impact]
 * TSC clocksource not available in nested guests

[Test Case]
 * Spin up a nested Xenial/Bionic guest and check for 'tsc' at
   /sys/devices/system/clocksource/clocksource0/available_clocksource

[Regression Potential]
 * The regression potential is low. Upstream code still maintains this
   behaviour of skipping calibration on guests, and tsc code verifies if
   the frequency is known before registering the clocksource

 * Patches were verified against the above test case, and also tested
   with stress-ng in both nested and non-nested guest scenarios

[Fix]
 * By applying the upstream commits, we skip refined calibration and
   register TSC as a clocksource directly if its frequency is known (via
   MSR or CPUID)

[Other Info]
 * Xenial needs 2 patches, Bionic needs 1 patch
 * Cosmic onwards (kernels 4.18+) are already fixed

Bin Gao (1):
  x86/tsc: Add X86_FEATURE_TSC_KNOWN_FREQ flag

Peng Hao (1):
  kvmclock: fix TSC calibration for nested guests

 arch/x86/include/asm/cpufeatures.h |  1 +
 arch/x86/kernel/kvmclock.c         |  1 +
 arch/x86/kernel/tsc.c              | 11 ++++++++---
 3 files changed, 10 insertions(+), 3 deletions(-)

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2.21.0