ACK: [SRU][F][PATCH v2 0/2] KVM: s390: pv: don't allow userspace to set the clock under PV

[Stefan Bader]

On 17.02.23 11:29, Roxana Nicolescu wrote:
> BugLink: https://bugs.launchpad.net/bugs/1999882
> 
> [Impact]
> Timer issues and RCU stalls after suspending and resuming an IBM SE guest.
> 
> 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.
> 
> [Fix]
> 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.
> 
> [Test]
> 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 should be 1 second. It used to be longer than 1 sec.
> 
> [Regression Potential]
> Minor but it may cause some timer issues on the kvm SE quest side.
> 
> [Note]
> Patch KVM: s390: pv: don't allow userspace to set the clock under PV
> was applied from upstream to jammy and kinetic.
> This set cherry-picks the commit for focal too.
> Another commit KVM: s390x: fix SCK locking had to cherry-picked as well
> in order to apply the changes properly.
> 
> v2:
> * Added details about the adjustments needed for backporting the commits.
> 
> Claudio Imbrenda (1):
>    KVM: s390x: fix SCK locking
> 
> Nico Boehr (1):
>    KVM: s390: pv: don't allow userspace to set the clock under PV
> 
>   Documentation/virt/kvm/devices/vm.txt |  4 ++++
>   arch/s390/kvm/kvm-s390.c              | 31 ++++++++++++++++++++++-----
>   arch/s390/kvm/kvm-s390.h              |  3 +--
>   arch/s390/kvm/priv.c                  | 15 ++++++++++++-
>   4 files changed, 45 insertions(+), 8 deletions(-)
> 

Acked-by: Stefan Bader <stefan.bader at canonical.com>
-- 
- Stefan

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