Re: [PATCH] target/s390x/kvm: Enable adapter interruption suppression again

[Cornelia Huck <cohuck@redhat.com>]

On Thu, 16 Jan 2020 15:19:13 -0500
Matthew Rosato <mjrosato@linux.ibm.com> wrote:

> On 1/16/20 7:20 AM, Thomas Huth wrote:
> > The AIS feature has been disabled late in the v2.10 development
> > cycle since there were some issues with migration (see commit
> > 3f2d07b3b01ea61126b - "s390x/ais: for 2.10 stable: disable ais
> > facility"). We originally wanted to enable it again for newer
> > machine types, but apparently we forgot to do this so far. Let's
> > do it for the new s390-ccw-virtio-5.0 machine now.
> > 
> > Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1756946
> > Signed-off-by: Thomas Huth <thuth@redhat.com>
> > ---
> >   hw/s390x/s390-virtio-ccw.c         |  4 ++++
> >   include/hw/s390x/s390-virtio-ccw.h |  4 ++++
> >   target/s390x/kvm.c                 | 11 ++++++++---
> >   3 files changed, 16 insertions(+), 3 deletions(-)

(...)

> > diff --git a/target/s390x/kvm.c b/target/s390x/kvm.c
> > index 15260aeb9a..4c1c8c0208 100644
> > --- a/target/s390x/kvm.c
> > +++ b/target/s390x/kvm.c
> > @@ -329,6 +329,8 @@ static void ccw_machine_class_foreach(ObjectClass *oc, void *opaque)
> >   
> >   int kvm_arch_init(MachineState *ms, KVMState *s)
> >   {
> > +    S390CcwMachineClass *smc = S390_CCW_MACHINE_OBJ_GET_CLASS(ms);
> > +  
> 
> I still can't run a proper test due to unavailable hw but in the 
> meantime I tried to virsh define a libvirt guest pointed at qemu (master 
> + this patch).  Regardless of machine type (s390-ccw-virtio-5.0 or 
> s390-ccw-virtio-4.2) I get:
> 
> virsh define guest.xml
> error: Failed to define domain from /path/to/guest.xml
> error: invalid argument: could not find capabilities for arch=s390x 
> domaintype=kvm
> 
> Similarly:
> 
> virsh domcapabilities
> error: failed to get emulator capabilities
> error: invalid argument: unable to find any emulator to serve 's390x' 
> architecture
> 
> Rolling back to qemu master, the define and domcapabilities work (with 
> no ais of course).
> 
> So: there is some incompatibility between the way libvirt invokes qemu 
> to detect capabilities and this code.  The above line seems to be the 
> root problem - if I take your patch and remove 'smc' then libvirt works 
> as expected and I can see ais in the domcapabilities.
> 
> Looking at those wrappers David mentioned...  I suspect you need this 
> for the 'none' machine case.  I tried a quick hack with the following:
> 
> bool ais_allowed(void)
> {
>      /* for "none" machine this results in true */
>      return get_machine_class()->kvm_ais_allowed;
> }
> 
> and
> 
> if (ais_allowed() &&
>      kvm_check_extension(s, KVM_CAP_S390_AIS_MIGRATION)) {
>      kvm_vm_enable_cap(s, KVM_CAP_S390_AIS, 0);
> }
> 
> This works and doesn't break libvirt compatibility detection.

Oh, "none" machine fun again... I think you're on the right track, and
we really need a wrapper.