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linux/Documentation/virt/kvm
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Nico Boehr 119407dc32 KVM: s390: pv: don't allow userspace to set the clock under PV 
[ Upstream commit 6973091d1b ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2022-11-16 09:58:17 +01:00
..
arm KVM: arm64: Fix Function ID typo for PTP_KVM service 2021-04-20 17:19:08 +01:00
devices KVM: s390: pv: don't allow userspace to set the clock under PV 2022-11-16 09:58:17 +01:00
amd-memory-encryption.rst x86/msr: Rename MSR_K8_SYSCFG to MSR_AMD64_SYSCFG 2021-05-10 07:51:38 +02:00
api.rst ARM: 2021-09-07 13:40:51 -07:00
cpuid.rst KVM: X86: Introduce KVM_HC_MAP_GPA_RANGE hypercall 2021-06-17 14:25:39 -04:00
halt-polling.rst docs: virt: convert halt-polling.txt to ReST format 2020-02-12 20:09:50 +01:00
hypercalls.rst KVM: X86: Introduce KVM_HC_MAP_GPA_RANGE hypercall 2021-06-17 14:25:39 -04:00
index.rst docs/virt/kvm: Document configuring and running nested guests 2020-05-06 05:45:47 -04:00
locking.rst Merge branch 'kvm-tdpmmu-fixes' into HEAD 2021-08-13 03:35:01 -04:00
mmu.rst KVM: x86/mmu: Rename "nxe" role bit to "efer_nx" for macro shenanigans 2021-06-24 18:00:41 -04:00
msr.rst KVM: X86: Introduce KVM_HC_MAP_GPA_RANGE hypercall 2021-06-17 14:25:39 -04:00
nested-vmx.rst KVM: Documentation: Fix documentation for nested. 2021-01-28 13:03:14 -05:00
ppc-pv.rst docs: kvm: Convert ppc-pv.txt to ReST format 2020-02-12 20:10:05 +01:00
review-checklist.rst docs: fix broken references for ReST files that moved around 2020-04-20 15:45:03 -06:00
running-nested-guests.rst KVM: Documentation: Fix documentation for nested. 2021-01-28 13:03:14 -05:00
s390-diag.rst KVM: s390: diag9c (directed yield) forwarding 2021-03-09 10:16:26 +01:00
s390-pv-boot.rst docs: virt: kvm: s390-pv-boot.rst: avoid using ReST :doc:foo markup 2021-06-17 13:24:39 -06:00
s390-pv.rst Documentation: virt: kvm/s390-pv: drop doubled words 2020-07-05 14:42:17 -06:00
timekeeping.rst docs: kvm: Convert timekeeping.txt to ReST format 2020-02-12 20:10:06 +01:00
vcpu-requests.rst This was a reasonably active cycle for documentation; this pull includes: 2021-06-28 16:53:05 -07:00