Comment 2 for bug 1822821

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.