Re: [RFC PATCH v2 1/1] KVM: s390: pv: don't allow userspace to set the clock under PV

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



Quoting Nico Boehr (2022-08-29 09:56:02)
> 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.
> 
> Fixes: 0f3035047140 ("KVM: s390: protvirt: Do only reset registers that are accessible")

I missed a 

Reported-by: Marc Hartmayer <mhartmay@xxxxxxxxxxxxx>

here. Sorry Marc.




[Index of Archives]     [KVM ARM]     [KVM ia64]     [KVM ppc]     [Virtualization Tools]     [Spice Development]     [Libvirt]     [Libvirt Users]     [Linux USB Devel]     [Linux Audio Users]     [Yosemite Questions]     [Linux Kernel]     [Linux SCSI]     [XFree86]

  Powered by Linux