On 10/27/2017 02:31 PM, Halil Pasic wrote:
On 10/25/2017 08:13 PM, Jason J. Herne wrote:
On 10/20/2017 10:54 AM, Christian Borntraeger wrote:
Starting a guest with <os> <type arch='s390x' machine='s390-ccw-virtio-2.9'>hvm</type> </os> <cpu mode='host-model'/>
on an IBM z14 results in
"qemu-system-s390x: Some features requested in the CPU model are not available in the configuration: gs"
This is because guarded storage is fenced for compat machines that did not have guarded storage support, but libvirt expands the cpu model according to the latest available machine.
While this prevents future migration abort (by not starting the guest at all), not being able to start a "host-model" guest is very much unexpected. As it turns out, even if we would modify libvirt to not expand the cpu model to contain "gs" for compat machines, it cannot guarantee that a migration will succeed. For example if the kernel changes its features (or the user has nested=1 on one host but not on the other) the migration will fail nevertheless. So instead of fencing "gs" for machines <= 2.9 lets allow it for all machine types that support the CPU model. This will make "host-model" runnable all the time, while relying on the CPU model to reject invalid migration attempts. ... - if (gs_allowed()) { + if (cpu_model_allowed()) { if (kvm_vm_enable_cap(s, KVM_CAP_S390_GS, 0) == 0) { cap_gs = 1;
@Jason
Hi Jason,
I don't have access to a z14 at the moment, and since you do, I would like to try out something.
I will first describe my concern, and then the test scenario.
The last line above, cap_gs = 1, has the side effect of returning true ever after.
int kvm_s390_get_gs(void) { return cap_gs; }
Now considering static bool gscb_needed(void *opaque) { return kvm_s390_get_gs(); }
Yes, we should also replace that with return s390_has_feat(S390_FEAT_GUARDED_STORAGE) I can fixup my patch or provide a 2nd one.