** Changed in: ubuntu-z-systems
Status: Fix Committed => Fix Released
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https://bugs.launchpad.net/bugs/1999882
Title:
[UBUNTU 20.04] KVM: s390: pv: don't allow userspace to set the clock
under PV - kernel part
Status in Ubuntu on IBM z Systems:
Fix Released
Status in linux package in Ubuntu:
Fix Released
Status in linux source package in Focal:
Fix Released
Status in linux source package in Jammy:
Fix Released
Status in linux source package in Kinetic:
Fix Released
Status in linux source package in Lunar:
Fix Released
Bug description:
Description: KVM: s390: pv: don't allow userspace to set the clock
under PV
Symptom: Timer issues and RCU stalls after suspending and
resuming an IBM Secure Execution guest
Problem: KVM and QEMU try to set the guest's TOD clock after resume
under PV, even though that is not permitted under SE.
Hence,their view of the guest clock may deviate from the
ultravisor's, possibly causing KVM to re-dispatch the
guest too late on clock comparator interrupts.
Solution: Don't set the clock after resume under PV. Note that kernel
and QEMU patches are required in lockstep,
to avoid a warning message in QEMU.
Reproduction: 1. Start SE guest using libvirt.
2. Pause the guest using "virsh suspend", wait for a few
seconds, resume using "virsh resume".
3. Run "time sleep 1" in the guest.
4. The sleep will sleep much longer than one second.
Upstream-ID: 6973091d1b50ab4042f6a2d495f59e9db3662ab8
Preventive fix: yes
Author: Nico Boehr <[email protected]>
Please note that fixing the described problem requires patches for the kernel
as well as for QEMU.
This bug covers the kernel part, whereas the required QEMU part is described
and handled in the following related bug:
Bug?200901 - [UBUNTU 20.04] KVM: s390: pv: don't allow userspace to
set the clock under PV - qemu part
Both parts, the kernel and the qemu patches should be applied / released at
the same time to avoid problems resulting in the following warning message for
customers:
'warning: Unable to set KVM guest TOD clock: Operation not supported'
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