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

[Christian Borntraeger]

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?

> 
> Thanks a lot for the testing, Matthew!
> 
>  Thomas
>