** Changed in: linux (Ubuntu Bionic)
Status: Confirmed => Fix Committed
** Changed in: linux (Ubuntu Xenial)
Status: Confirmed => Fix Committed
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https://bugs.launchpad.net/bugs/1822821
Title:
TSC clocksource not available in nested guests
Status in linux package in Ubuntu:
Fix Released
Status in linux source package in Xenial:
Fix Committed
Status in linux source package in Bionic:
Fix Committed
Bug description:
[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 [0] [1], we skip refined calibration and
register TSC as a clocksource directly if its frequency is known (via
MSR or CPUID)
* Cosmic onwards (kernel 4.18+) are already fixed
[0] For Xenial only - https://git.kernel.org/linus/47c95a46d0f
[1] https://git.kernel.org/linus/e10f78050323
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