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

[Cornelia Huck <cohuck@redhat.com>]

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/

>       */
> -    /* 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?