Re: [PATCH v3] target/s390x/kvm: Enable adapter interruption suppression again

[Cornelia Huck <cohuck@redhat.com>]

On Tue, 21 Jan 2020 09:33:02 -0500
Matthew Rosato <mjrosato@linux.ibm.com> wrote:

> On 1/20/20 12:27 PM, Cornelia Huck wrote:
> > On Mon, 20 Jan 2020 14:24:41 +0100
> > Thomas Huth <thuth@redhat.com> 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.
> >>
> >> While at it, also add a more verbose comment why we need the *_allowed()
> >> wrappers in s390-virtio-ccw.c.
> >>
> >> Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1756946
> >> Reviewed-by: David Hildenbrand <david@redhat.com>
> >> Signed-off-by: Thomas Huth <thuth@redhat.com>
> >> ---
> >>   v3: Moved "s390mc->kvm_ais_allowed = false" to the end of the function
> >>
> >>   hw/s390x/s390-virtio-ccw.c         | 20 +++++++++++++++++---
> >>   include/hw/s390x/s390-virtio-ccw.h |  3 +++
> >>   target/s390x/kvm.c                 |  9 ++++++---
> >>   3 files changed, 26 insertions(+), 6 deletions(-)  
> >   
> >> diff --git a/target/s390x/kvm.c b/target/s390x/kvm.c
> >> index 15260aeb9a..cf4fb4f2d9 100644
> >> --- a/target/s390x/kvm.c
> >> +++ b/target/s390x/kvm.c
> >> @@ -365,10 +365,13 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
> >>       /*
> >>        * The migration interface for ais was introduced with kernel 4.13
> >>        * but the capability itself had been active since 4.12. As migration
> >> -     * support is considered necessary let's disable ais in the 2.10
> >> -     * machine.
> >> +     * support is considered necessary, we only try to enable this for
> >> +     * newer machine types if KVM_CAP_S390_AIS_MIGRATION is available.
> >>        */
> >> -    /* kvm_vm_enable_cap(s, KVM_CAP_S390_AIS, 0); */
> >> +    if (kvm_ais_allowed() &&
> >> +        kvm_check_extension(s, KVM_CAP_S390_AIS_MIGRATION)) {  
> > 
> > Hnm, we actually need a kernel irqchip with the kvm flic to get ais to
> > work; else we'll fail with
> > 
> > qemu-system-s390x: Failed to inject airq with AIS supported
> > 
> > in the kernel_irqchip=off case, as we won't have an I/O adapter
> > registered.
> > 
> > Adding 'kvm_kernel_irqchip_required() &&' seems to do the trick;
> > comments?
> >   
> 
> In spirit, I agree with this idea.  But, a quick test shows that putting 
> this check here results in ais=off for the 'none' machine case (libvirt 
> capabilities detection).  I think we have to only look at 
> kvm_kernel_irqchip_required() when working with a real machine.

Sigh, I think you're right again. We need to check for the 'none'
machine here; but I can't think of a non-ugly way to do so...

> 
> >> +        kvm_vm_enable_cap(s, KVM_CAP_S390_AIS, 0);
> >> +    }
> >>   
> >>       kvm_set_max_memslot_size(KVM_SLOT_MAX_BYTES);
> >>       return 0;  
> > 
> >   
>