From: Nico Boehr <nrb@linux.ibm.com>
To: kvm@vger.kernel.org
Cc: frankja@linux.ibm.com, imbrenda@linux.ibm.com, borntraeger@linux.ibm.com
Subject: [PATCH v3 0/2] KVM: s390: pv: fix clock comparator late after suspend/resume
Date: Wed, 5 Oct 2022 18:32:56 +0200 [thread overview]
Message-ID: <20221005163258.117232-1-nrb@linux.ibm.com> (raw)
v2->v3:
---
- add commit to remove kvm_s390_set_tod_clock() function (thanks Claudio)
v1->v2:
---
- fix broken migration due to deadlock
After a PV guest in QEMU has been paused and resumed, clock comparator
interrupts are delivered to the guest much too late.
This is caused by QEMU's tod-kvm device restoring the guest's TOD clock
upon guest resume. This is not possible with PV, since the guest's TOD
clock is controlled by the ultravisor.
Even if not allowed under PV, KVM allowed the respective call from
userspace (VM attribute KVM_S390_VM_TOD) and updated its internal data
structures on this call. This can make the ultravisor's and KVM's view
of the guest TOD clock inconsistent. This in turn can lead to the late
delivery of clock comparator interrupts when KVM calculates when to wake
the guest.
This fixes the kernel portion of the problem by disallowing the vm attr
call for the guest TOD clock so userspace cannot mess up KVM's view of
the guest TOD. This fix causes an ugly warning in QEMU though, hence
another fix is due for QEMU to simply not even attempt to set the guest
TOD on resume.
Nico Boehr (2):
KVM: s390: pv: don't allow userspace to set the clock under PV
KVM: s390: remove now unused function kvm_s390_set_tod_clock
arch/s390/kvm/kvm-s390.c | 22 +++++++++++++---------
arch/s390/kvm/kvm-s390.h | 1 -
2 files changed, 13 insertions(+), 10 deletions(-)
--
2.36.1
next reply other threads:[~2022-10-05 16:33 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-05 16:32 Nico Boehr [this message]
2022-10-05 16:32 ` [PATCH v3 1/2] KVM: s390: pv: don't allow userspace to set the clock under PV Nico Boehr
2022-10-05 17:01 ` Claudio Imbrenda
2022-10-10 15:20 ` Janosch Frank
2022-10-11 8:41 ` Nico Boehr
2022-10-05 16:32 ` [PATCH v3 2/2] KVM: s390: remove now unused function kvm_s390_set_tod_clock Nico Boehr
2022-10-05 17:01 ` Claudio Imbrenda
2022-10-10 15:23 ` Janosch Frank
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