MMIO/PIO address->device structure mapping (kvm->buses).
The srcu index can be stored in kvm_vcpu->srcu_idx per vcpu
if it is needed by multiple functions.
+
+Name: blocked_vcpu_on_cpu_lock
+Type: spinlock_t
+Arch: x86
+Protects: blocked_vcpu_on_cpu
+Comment: This is a per-CPU lock and it is used for VT-d posted-interrupts.
+ When VT-d posted-interrupts is supported and the VM has assigned
+ devices, we put the blocked vCPU on the list blocked_vcpu_on_cpu
+ protected by blocked_vcpu_on_cpu_lock, when VT-d hardware issues
+ wakeup notification event since external interrupts from the
+ assigned devices happens, we will find the vCPU on the list to
+ wakeup.