kvm: introduce KVM_MAX_VCPU_ID

The KVM_MAX_VCPUS define provides the maximum number of vCPUs per guest, and also the upper limit for vCPU ids. This is okay for all archs except PowerPC which can have higher ids, depending on the cpu/core/thread topology. In the worst case (single threaded guest, host with 8 threads per core), it limits the maximum number of vCPUS to KVM_MAX_VCPUS / 8. This patch separates the vCPU numbering from the total number of vCPUs, with the introduction of KVM_MAX_VCPU_ID, as the maximal valid value for vCPU ids plus one. The corresponding KVM_CAP_MAX_VCPU_ID allows userspace to validate vCPU ids before passing them to KVM_CREATE_VCPU. This patch only implements KVM_MAX_VCPU_ID with a specific value for PowerPC. Other archs continue to return KVM_MAX_VCPUS instead.

GKGreg Kurz committed 10 years ago