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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'
** Affects: linux (Ubuntu)
Importance: Undecided
Assignee: Skipper Bug Screeners (skipper-screen-team)
Status: New
** Tags: architecture-s39064 bugnameltc-200889 severity-high
targetmilestone-inin---
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[UBUNTU 20.04] KVM: s390: pv: don't allow userspace to set the clock under PV -
kernel part
https://bugs.launchpad.net/bugs/1999882
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