Re: [Qemu-devel] [PATCH/s390-next 3/3] s390x/flic: migrate ais states

[Cornelia Huck <cohuck@redhat.com>]

On Thu, 13 Jul 2017 15:02:08 +0200
Christian Borntraeger <borntraeger@de.ibm.com> wrote:

> On 07/13/2017 02:27 PM, Cornelia Huck wrote:
> > On Thu, 13 Jul 2017 12:40:29 +0200
> > Christian Borntraeger <borntraeger@de.ibm.com> wrote:
> >   
> >> From: Yi Min Zhao <zyimin@linux.vnet.ibm.com>
> >>
> >> During migration we should transfer ais states to the target guest.
> >> This patch introduces a subsection to kvm_s390_flic_vmstate and new
> >> vmsd for qemu_flic. The ais states need to be migrated only when
> >> ais is supported.
> >>
> >> Signed-off-by: Yi Min Zhao <zyimin@linux.vnet.ibm.com>
> >> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
> >> ---
> >>  hw/intc/s390_flic.c          | 20 ++++++++++++
> >>  hw/intc/s390_flic_kvm.c      | 75 ++++++++++++++++++++++++++++++++++++++++++++
> >>  include/hw/s390x/s390_flic.h |  1 +
> >>  3 files changed, 96 insertions(+)

> >> +static int kvm_flic_ais_post_load(void *opaque, int version_id)
> >> +{
> >> +    KVMS390FLICStateMigTmp *tmp = opaque;
> >> +    KVMS390FLICState *flic = tmp->parent;
> >> +    struct kvm_s390_ais_all ais = {
> >> +        .simm = tmp->simm,
> >> +        .nimm = tmp->nimm,
> >> +    };
> >> +    struct kvm_device_attr attr = {
> >> +        .group = KVM_DEV_FLIC_AISM_ALL,
> >> +        .addr = (uint64_t)&ais,
> >> +    };
> >> +
> >> +    if (!ais_needed(flic)) {
> >> +        return -ENOSYS;
> >> +    }  
> > 
> > I do not understand this... does that mean that
> > - we should never get here or 
> > - we should not try to change the fields or
> > - I need coffee?  
> 
> My understanding is that this should not happen with a normal setup, 
> but it can happen if the user does something "wrong". For example
> use qemu without libvirt and with -cpu host (which is not migration safe)
> and do a migration from a host that has AIS to a host that has no AIS.
> In that case the target system will reject the migration (late, but hopefully
> not too late).

A comment would be helpful here.