linux/arch/s390/kvm
Nico Boehr 6973091d1b KVM: s390: pv: don't allow userspace to set the clock under PV
When running under PV, the guest's TOD clock is under control of the
ultravisor and the hypervisor isn't allowed to change it. Hence, don't
allow userspace to change the guest's TOD clock by returning
-EOPNOTSUPP.

When userspace changes the guest's TOD clock, KVM updates its
kvm.arch.epoch field and, in addition, the epoch field in all state
descriptions of all VCPUs.

But, under PV, the ultravisor will ignore the epoch field in the state
description and simply overwrite it on next SIE exit with the actual
guest epoch. This leads to KVM having an incorrect view of the guest's
TOD clock: it has updated its internal kvm.arch.epoch field, but the
ultravisor ignores the field in the state description.

Whenever a guest is now waiting for a clock comparator, KVM will
incorrectly calculate the time when the guest should wake up, possibly
causing the guest to sleep for much longer than expected.

With this change, kvm_s390_set_tod() will now take the kvm->lock to be
able to call kvm_s390_pv_is_protected(). Since kvm_s390_set_tod_clock()
also takes kvm->lock, use __kvm_s390_set_tod_clock() instead.

The function kvm_s390_set_tod_clock is now unused, hence remove it.
Update the documentation to indicate the TOD clock attr calls can now
return -EOPNOTSUPP.

Fixes: 0f30350471 ("KVM: s390: protvirt: Do only reset registers that are accessible")
Reported-by: Marc Hartmayer <mhartmay@linux.ibm.com>
Signed-off-by: Nico Boehr <nrb@linux.ibm.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
Link: https://lore.kernel.org/r/20221011160712.928239-2-nrb@linux.ibm.com
Message-Id: <20221011160712.928239-2-nrb@linux.ibm.com>
Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
2022-11-07 10:14:15 +01:00
..
diag.c KVM: s390: restore old debugfs names 2021-07-27 16:59:00 -04:00
gaccess.c KVM: s390: Pass initialized arg even if unused 2022-09-21 16:18:35 +02:00
gaccess.h KVM: s390: Cleanup ipte lock access and SIIF facility checks 2022-07-20 10:57:36 +02:00
guestdbg.c KVM: s390: Add memcg accounting to KVM allocations 2020-12-10 13:36:05 +01:00
intercept.c KVM: s390: pv: don't present the ecall interrupt twice 2022-07-19 15:48:14 +02:00
interrupt.c KVM: s390: pci: fix GAIT physical vs virtual pointers usage 2022-09-21 16:18:38 +02:00
irq.h KVM: s390: Remove redundant license text 2017-12-06 09:18:42 +01:00
Kconfig KVM: s390: pv: add mmu_notifier 2022-07-19 12:05:57 +00:00
kvm-s390.c KVM: s390: pv: don't allow userspace to set the clock under PV 2022-11-07 10:14:15 +01:00
kvm-s390.h KVM: s390: pv: don't allow userspace to set the clock under PV 2022-11-07 10:14:15 +01:00
Makefile KVM: s390: pci: add basic kvm_zdev structure 2022-07-11 09:54:27 +02:00
pci.c KVM: s390: pci: register pci hooks without interpretation 2022-09-21 16:18:38 +02:00
pci.h KVM: s390: pci: fix plain integer as NULL pointer warnings 2022-09-21 16:18:30 +02:00
priv.c KVM: s390: guest support for topology function 2022-07-20 10:57:36 +02:00
pv.c KVM: s390: pv: destroy the configuration before its memory 2022-07-19 12:06:56 +00:00
sigp.c KVM: s390: pv: don't present the ecall interrupt twice 2022-07-19 15:48:14 +02:00
trace-s390.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
trace.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
vsie.c KVM: s390: guest support for topology function 2022-07-20 10:57:36 +02:00