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

[Cornelia Huck <cohuck@redhat.com>]

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?

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