From: David Hildenbrand <dahi@xxxxxxxxxxxxxxxxxx> We should never allow to enable/disable any facilities for the guest when other VCPUs were already created. kvm_arch_vcpu_(load|put) relies on SIMD not changing during runtime. If somebody would create and run VCPUs and then decides to enable SIMD, undefined behaviour could be possible (e.g. vector save area not being set up). Acked-by: Christian Borntraeger <borntraeger@xxxxxxxxxx> Acked-by: Cornelia Huck <cornelia.huck@xxxxxxxxxx> Signed-off-by: David Hildenbrand <dahi@xxxxxxxxxxxxxxxxxx> Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx # 4.1+ --- arch/s390/kvm/kvm-s390.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c index 8fe2f1c..8465892 100644 --- a/arch/s390/kvm/kvm-s390.c +++ b/arch/s390/kvm/kvm-s390.c @@ -342,12 +342,16 @@ static int kvm_vm_ioctl_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap) r = 0; break; case KVM_CAP_S390_VECTOR_REGISTERS: - if (MACHINE_HAS_VX) { + mutex_lock(&kvm->lock); + if (atomic_read(&kvm->online_vcpus)) { + r = -EBUSY; + } else if (MACHINE_HAS_VX) { set_kvm_facility(kvm->arch.model.fac->mask, 129); set_kvm_facility(kvm->arch.model.fac->list, 129); r = 0; } else r = -EINVAL; + mutex_unlock(&kvm->lock); VM_EVENT(kvm, 3, "ENABLE: CAP_S390_VECTOR_REGISTERS %s", r ? "(not available)" : "(success)"); break; -- 2.3.0 -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html