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

[Cornelia Huck <cohuck@redhat.com>]

On Thu, 13 Jul 2017 15:58:30 +0200
Christian Borntraeger <borntraeger@de.ibm.com> wrote:

> On 07/13/2017 03:10 PM, Cornelia Huck wrote:
> > 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.  
> 
> Something like
> 
> diff --git a/hw/intc/s390_flic_kvm.c b/hw/intc/s390_flic_kvm.c
> index 4cf73ee..9b8dbd1 100644
> --- a/hw/intc/s390_flic_kvm.c
> +++ b/hw/intc/s390_flic_kvm.c
> @@ -452,6 +452,12 @@ static int kvm_flic_ais_post_load(void *opaque, int version_id)
>          .addr = (uint64_t)&ais,
>      };
>  
> +    /* This can happen when the user mis-configures its guests in an
> +     * incompatible fashion or without a CPU model. For example using
> +     * qemu 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 here.
> +     */
>      if (!ais_needed(flic)) {
>          return -ENOSYS;
>      }

With that added:

Reviewed-by: Cornelia Huck <cohuck@redhat.com>