KVM: s390: enable SIMD only when no VCPUs were created

commit 5967c17b118a2bd1dd1d554cc4eee16233e52bec upstream.

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@de.ibm.com>
Acked-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 2275413625dbc482a273339300edf1f1b773357d..1290af83417a303479cbe0395c3c88bb57b78d34 100644 (file)
--- 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;