Re: [libvirt] Question about the host-model CPU mode

On 10/20/2017 03:51 PM, David Hildenbrand wrote: [...] >> The problem goes much further. >> A fresh guest with >> >> <os> >> <type arch='s390x' machine='s390-ccw-virtio-2.9'>hvm</type> >> </os> >> <cpu mode='host-model'/> >> >> does not start. No migration from an older system is necessary. >> > > Yes, as stated in the documentation "copying host CPU definition from > capabilities XML" this can not work. And it works just as documented. > Not saying this is a nice thing :) > > I think we should try to fix gs_allowed (if possible) and avoid > something like that in the future. This would avoid other complexity > involved when suddenly having X host models. Maybe this one is really a proper fix. It will allow the guest to start and on migration the cpu model will complain if the target cannot provide gs. Similar things can happen if - for example - the host kernel lacks some features.

diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c index 77169bb..97a08fa 100644 --- a/hw/s390x/s390-virtio-ccw.c +++ b/hw/s390x/s390-virtio-ccw.c @@ -430,7 +430,6 @@ static void ccw_machine_class_init(ObjectClass *oc, void *data) s390mc->ri_allowed = true; s390mc->cpu_model_allowed = true; s390mc->css_migration_enabled = true; - s390mc->gs_allowed = true; mc->init = ccw_init; mc->reset = s390_machine_reset; mc->hot_add_cpu = s390_hot_add_cpu; @@ -509,12 +508,6 @@ bool cpu_model_allowed(void) return get_machine_class()->cpu_model_allowed; } -bool gs_allowed(void) -{ - /* for "none" machine this results in true */ - return get_machine_class()->gs_allowed; -} - static char *machine_get_loadparm(Object *obj, Error **errp) { S390CcwMachineState *ms = S390_CCW_MACHINE(obj); @@ -757,7 +750,6 @@ static void ccw_machine_2_9_class_options(MachineClass *mc) { S390CcwMachineClass *s390mc = S390_MACHINE_CLASS(mc); - s390mc->gs_allowed = false; ccw_machine_2_10_class_options(mc); SET_MACHINE_COMPAT(mc, CCW_COMPAT_2_9); s390mc->css_migration_enabled = false; diff --git a/include/hw/s390x/s390-virtio-ccw.h b/include/hw/s390x/s390-virtio-ccw.h index a9a90c2..1de53b0 100644 --- a/include/hw/s390x/s390-virtio-ccw.h +++ b/include/hw/s390x/s390-virtio-ccw.h @@ -40,7 +40,6 @@ typedef struct S390CcwMachineClass { bool ri_allowed; bool cpu_model_allowed; bool css_migration_enabled; - bool gs_allowed; } S390CcwMachineClass; /* runtime-instrumentation allowed by the machine */ diff --git a/target/s390x/kvm.c b/target/s390x/kvm.c index a0d5052..3f13fc2 100644 --- a/target/s390x/kvm.c +++ b/target/s390x/kvm.c @@ -362,7 +362,7 @@ int kvm_arch_init(MachineState *ms, KVMState *s) cap_ri = 1; } } - if (gs_allowed()) { + if (cpu_model_allowed()) { if (kvm_vm_enable_cap(s, KVM_CAP_S390_GS, 0) == 0) { cap_gs = 1; }