hyperv/vmbus: Avoid extra copy of page information.

[sepherosa_gmail.com]

Summary

The page information array could contain up to 32 elements (i.e. 512B). And on network side w/ TSO, 11+ (176B+) elements, i.e. ~44K TSO packet, in the page information array is quite common.

This saves us some cpu cycles.

head/sys/dev/hyperv/vmbus/hv_channel.c

while (1) {
                 if (intr_disabled) {
                         wmesg = "vmhalt";
                         VCPU_CTR0(vm, vcpuid, "Halted");
                         if (!vcpu_halted && halt_detection_enabled) {
                                 vcpu_halted = 1;
                                 CPU_SET_ATOMIC(vcpuid, &vm->halted_cpus);
                         }
                         if (CPU_CMP(&vm->halted_cpus, &vm->active_cpus) == 0) {
                                 vm_halted = 1;
                                 break;
                         }
                 } else {
                         wmesg = "vmidle";
                 }
 
                 t = ticks;
                 vcpu_require_state_locked(vm, vcpuid, VCPU_SLEEPING);
                 /*
                  * XXX msleep_spin() cannot be interrupted by signals so
                  * wake up periodically to check pending signals.
                  */
                 msleep_spin(vcpu, &vcpu->mtx, wmesg, hz);
                 vcpu_require_state_locked(vm, vcpuid, VCPU_FROZEN);
                 vmm_stat_incr(vm, vcpuid, VCPU_IDLE_TICKS, ticks - t);
                 if (td_ast_pending(td, TDA_SUSPEND)) {
                         vcpu_unlock(vcpu);
                         error = thread_check_susp(td, false);
-                        if (error != 0)
+                        if (error != 0) {
+                                if (vcpu_halted) {
+                                        CPU_CLR_ATOMIC(vcpuid,
+                                            &vm->halted_cpus);
+                                }
                                 return (error);
+                        }
                         vcpu_lock(vcpu);
                 }
         }
 
         if (vcpu_halted)
                 CPU_CLR_ATOMIC(vcpuid, &vm->halted_cpus);
 
         vcpu_unlock(vcpu);