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

[Matthew Rosato <mjrosato@linux.ibm.com>]

On 1/16/20 8:22 AM, Christian Borntraeger wrote:
> 
> 
> On 16.01.20 13:55, Thomas Huth wrote:
>> On 16/01/2020 13.50, Cornelia Huck wrote:
>>> On Thu, 16 Jan 2020 13:20:26 +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.
>>>>
>>>> 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(-)
>>>>
>>>
>>>> @@ -365,10 +367,13 @@ 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 enable this for newer
>>>
>>> s/necessary we only enable this/necessary, we only try to enable this/
>>>
>>>> +     * machine types and if KVM_CAP_S390_AIS_MIGRATION is available.
>>>
>>> maybe s/and if/if/
>>
>> Sure ... could you fix it up when picking up the patch (in case I don't
>> have to respin), or do you want me to send a v2?
>>
>>>>        */
>>>> -    /* kvm_vm_enable_cap(s, KVM_CAP_S390_AIS, 0); */
>>>> +    if (smc->kvm_ais_allowed &&
>>>> +        kvm_check_extension(s, KVM_CAP_S390_AIS_MIGRATION)) {
>>>> +        kvm_vm_enable_cap(s, KVM_CAP_S390_AIS, 0);
>>>> +    }
>>>>   
>>>>       kvm_set_max_memslot_size(KVM_SLOT_MAX_BYTES);
>>>>       return 0;
>>>
>>> Looks good.
>>>
>>> Remind me again: ais only made a difference for pci devices, right? Is
>>> it enough to give this a quick whirl with virtio-pci devices?
>>
>> I don't remember the details, Christian, could you please answer this
>> question?
> 
> Yes, IIRC AIS was there for PCI, but not for Crypto or virtio.

This matches my understanding as well.

> The patch looks sane, but it would be good if someone could try
> the AIS stuff.
> 
> Matt, can you have a look?

Sure.  But my PCI environment is currently down for a maintenance 
window, will try again later today.