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

[Thomas Huth]

On 17/01/2020 12.05, Christian Borntraeger wrote:
> 
> 
> On 17.01.20 11:38, Thomas Huth wrote:
>> On 16/01/2020 21.26, Cornelia Huck wrote:
>>> On Thu, 16 Jan 2020 15:19:13 -0500
>>> Matthew Rosato <address@hidden> 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 <address@hidden>
>>>>> ---
>>>>>   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.
>>
>> D'oh, so this is the real reason for the wrappers ... ok, I'll respin my
>> patch accordingly.
> 
> 
> Can you add a comment to the wrappers?

Yes, good idea, I'll do that!

 Thomas