Re: [PATCH v2 1/2] target/s390x/kvm: Turn KVM_CAP_SYNC_REGS into a hard requirement

[Thomas Huth]

On 10/10/2023 13.02, Christian Borntraeger wrote:
> Am 09.10.23 um 19:07 schrieb Thomas Huth:
> > Since we already require at least kernel 3.15 in the s390x KVM code,
> > we can assume that the KVM_CAP_SYNC_REGS capability is always there.
> > Thus turn this into a hard requirement now.
> >
> > Signed-off-by: Thomas Huth <thuth@redhat.com>
> > ---
> >   target/s390x/kvm/kvm.c | 20 ++++++++++++++------
> >   1 file changed, 14 insertions(+), 6 deletions(-)
> >
> > diff --git a/target/s390x/kvm/kvm.c b/target/s390x/kvm/kvm.c
> > index bc5c56a305..b3e2eaa2eb 100644
> > --- a/target/s390x/kvm/kvm.c
> > +++ b/target/s390x/kvm/kvm.c
> > @@ -337,21 +337,29 @@ int kvm_arch_get_default_type(MachineState *ms)
> >   int kvm_arch_init(MachineState *ms, KVMState *s)
> >   {
> > +    int required_caps[] = {
> > +        KVM_CAP_DEVICE_CTRL,
> > +        KVM_CAP_SYNC_REGS,
> > +    };
> > +
> > +    for (int i = 0; i < ARRAY_SIZE(required_caps); i++) {
> > +        if (!kvm_check_extension(s, required_caps[i])) {
> > +            error_report("KVM is missing capability #%d - "
> > +                         "please use kernel 3.15 or newer", 
> > required_caps[i]);
> > +            return -1;
> > +        }
> > +    }
> > +
> >       object_class_foreach(ccw_machine_class_foreach, TYPE_S390_CCW_MACHINE,
> >                            false, NULL);
> > -    if (!kvm_check_extension(kvm_state, KVM_CAP_DEVICE_CTRL)) {
> > -        error_report("KVM is missing capability KVM_CAP_DEVICE_CTRL - "
> > -                     "please use kernel 3.15 or newer");
> > -        return -1;
> > -    }
> >       if (!kvm_check_extension(s, KVM_CAP_S390_COW)) {
> >           error_report("KVM is missing capability KVM_CAP_S390_COW - "
> >                        "unsupported environment");
> >           return -1;
> >       }
>
> Not sure if we also want to move KVM_CAP_S390_COW somehow. The message would 
> be different.

IIRC that error could happen when you ran KVM within an older version of 
z/VM, so the "please use kernel 3.15 or newer" message would be completely 
misleading there.

> Aparch from that:
> Reviewed-by: Christian Borntraeger <borntraeger@linux.ibm.com>

Thanks,
  Thomas