Re: [PATCH v5] target/s390x/kvm: Enable adapter interruption suppression again

[Cornelia Huck]

On Wed, 22 Jan 2020 11:14:37 +0100
Thomas Huth <address@hidden> 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 now for the machines that support proper CPU models.
> 
> Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1756946
> Signed-off-by: Thomas Huth <address@hidden>
> ---
>  v5: Use cpu_model_allowed() as suggested by David. Seems to work as far
>      as I can test it without PCI cards, but ping-pong migration with
>      "-cpu host" from/to an older version of QEMU is now not working
>      anymore - but I think that's kind of expected since "-cpu host"
>      is not migration-safe anyway.

Ok, so I'll wait for test results with pci cards before queuing this :)

> 
>  target/s390x/kvm.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/target/s390x/kvm.c b/target/s390x/kvm.c
> index 15260aeb9a..30112e529c 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 (cpu_model_allowed() && kvm_kernel_irqchip_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;

Side note: as you do not add a new _allowed() function, you don't add
the clarifying comment anymore -- any value in doing so as a separate
patch? And maybe stating as well that new features of that type should
rely on the cpu model?