KVM: Restore missing powerpc API docs

single-threaded guest vcpus, it should make all vcpu ids be a multiple

of the number of vcpus per vcore.

On powerpc using book3s_hv mode, the vcpus are mapped onto virtual

threads in one or more virtual CPU cores.  (This is because the

hardware requires all the hardware threads in a CPU core to be in the

same partition.)  The KVM_CAP_PPC_SMT capability indicates the number

of vcpus per virtual core (vcore).  The vcore id is obtained by

dividing the vcpu id by the number of vcpus per vcore.  The vcpus in a

given vcore will always be in the same physical core as each other

(though that might be a different physical core from time to time).

Userspace can control the threading (SMT) mode of the guest by its

allocation of vcpu ids.  For example, if userspace wants

single-threaded guest vcpus, it should make all vcpu ids be a multiple

of the number of vcpus per vcore.

4.8 KVM_GET_DIRTY_LOG (vm ioctl)

Capability: basic