This is easily verifiable on both Xenial and Bionic guests from uvt-kvm. I've brought up both as nested instances, and TSC fails to show up as an available clocksource:
== Xenial guest == $ uvt-kvm ssh bionic-l1 ubuntu@bionic-l1:~$ uvt-kvm ssh xenial-l2 ubuntu@xenial-l2:~$ uname -r 4.4.0-143-generic ubuntu@xenial-l2:~$ cat /sys/devices/system/clocksource/clocksource0/available_clocksource kvm-clock hpet acpi_pm ubuntu@xenial-l2:~$ dmesg | grep -i tsc [ 0.000000] tsc: Detected 1997.676 MHz processor == Bionic guest == $ uvt-kvm ssh bionic-l1 ubuntu@bionic-l1:~$ uvt-kvm ssh bionic-l2 ubuntu@bionic-l2:~$ uname -r 4.15.0-46-generic ubuntu@bionic-l2:~$ cat /sys/devices/system/clocksource/clocksource0/available_clocksource kvm-clock hpet acpi_pm ubuntu@bionic-l2:~$ dmesg | grep -i tsc [ 0.052000] tsc: Detected 1997.676 MHz processor == >From what I've tested, it doesn't seem to matter which L1 kernel is running, since they usually have TSC available. This seems to be an issue only on nested guests. ** Description changed: [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 -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1822821 Title: TSC clocksource not available in nested guests Status in linux package in Ubuntu: Incomplete Status in linux source package in Xenial: Confirmed Status in linux source package in Bionic: Confirmed 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 To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1822821/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
