** Package changed: linux (Ubuntu) => qemu (Ubuntu)
** Also affects: ubuntu-z-systems
Importance: Undecided
Status: New
** Changed in: qemu (Ubuntu)
Importance: Undecided => High
** Changed in: ubuntu-z-systems
Importance: Undecided => High
** Changed in: ubuntu-z-systems
Assignee: (unassigned) => Skipper Bug Screeners (skipper-screen-team)
** Also affects: qemu (Ubuntu Lunar)
Importance: High
Assignee: Skipper Bug Screeners (skipper-screen-team)
Status: New
** Also affects: qemu (Ubuntu Jammy)
Importance: Undecided
Status: New
** Also affects: qemu (Ubuntu Focal)
Importance: Undecided
Status: New
** Also affects: qemu (Ubuntu Kinetic)
Importance: Undecided
Status: New
** Changed in: qemu (Ubuntu Lunar)
Importance: High => Low
** Changed in: ubuntu-z-systems
Status: New => Triaged
** Changed in: qemu (Ubuntu Lunar)
Assignee: Skipper Bug Screeners (skipper-screen-team) => Ubuntu Server
(ubuntu-server)
--
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/1999885
Title:
[UBUNTU 20.04] KVM: s390: pv: don't allow userspace to set the clock
under PV - qemu part
Status in Ubuntu on IBM z Systems:
Triaged
Status in qemu package in Ubuntu:
New
Status in qemu source package in Focal:
New
Status in qemu source package in Jammy:
New
Status in qemu source package in Kinetic:
New
Status in qemu source package in Lunar:
New
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.
Component: qemu
Upstream-ID: 38621181ae3cbec62e3490fbc14f6ac01642d07a
Preventive: yes
Author: Nico Boehr <n...@linux.ibm.com>
Please note that fixing the described problem requires patches for the kernel
as well as for QEMU.
This bug covers the qemu part, whereas the required kernel part is described
and handled in the following related bug:
Bug 200889 - [UBUNTU 20.04] KVM: s390: pv: don't allow userspace to set
the clock under PV - kernel 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'
To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu-z-systems/+bug/1999885/+subscriptions
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