s390x/kvm: enable AP instruction interpretation for guest

s390x/kvm: enable AP instruction interpretation for guest

Let's use the KVM_SET_DEVICE_ATTR ioctl to enable hardware
interpretation of AP instructions executed on the guest.
If the S390_FEAT_AP feature is switched on for the guest,
AP instructions must be interpreted by default; otherwise,
they will be intercepted.

This attribute setting may be overridden by a device. For example,
a device may want to provide AP instructions to the guest (i.e.,
S390_FEAT_AP turned on), but it may want to emulate them. In this
case, the AP instructions executed on the guest must be
intercepted; so when the device is realized, it must disable
interpretation.

Signed-off-by: Tony Krowiak <[email protected]>
Tested-by: Pierre Morel <[email protected]>
Reviewed-by: David Hildenbrand <[email protected]>
Reviewed-by: Thomas Huth <[email protected]>
Reviewed-by: Christian Borntraeger <[email protected]>
Acked-by: Halil Pasic <[email protected]>
Tested-by: Christian Borntraeger <[email protected]>
Message-Id: <20181010170309[email protected]>
Signed-off-by: Cornelia Huck <[email protected]>