KVM: arm/arm64: Let vcpu thread modify its own active state

static void vgic_mmio_change_active(struct kvm_vcpu *vcpu, struct vgic_irq *irq,

				    bool new_active_state)

{

	struct kvm_vcpu *requester_vcpu;

	spin_lock(&irq->irq_lock);

	/*

	 * The vcpu parameter here can mean multiple things depending on how

	 * this function is called; when handling a trap from the kernel it

	 * depends on the GIC version, and these functions are also called as

	 * part of save/restore from userspace.

	 *

	 * Therefore, we have to figure out the requester in a reliable way.

	 *

	 * When accessing VGIC state from user space, the requester_vcpu is

	 * NULL, which is fine, because we guarantee that no VCPUs are running

	 * when accessing VGIC state from user space so irq->vcpu->cpu is

	 * always -1.

	 */

	requester_vcpu = kvm_arm_get_running_vcpu();

	/*

	 * If this virtual IRQ was written into a list register, we

	 * have to make sure the CPU that runs the VCPU thread has

	 * synced back LR state to the struct vgic_irq.  We can only

	 * know this for sure, when either this irq is not assigned to

	 * anyone's AP list anymore, or the VCPU thread is not

	 * running on any CPUs.

	 * synced back the LR state to the struct vgic_irq.

	 *

	 * In the opposite case, we know the VCPU thread may be on its

	 * way back from the guest and still has to sync back this

	 * IRQ, so we release and re-acquire the spin_lock to let the

	 * other thread sync back the IRQ.

	 * As long as the conditions below are true, we know the VCPU thread

	 * may be on its way back from the guest (we kicked the VCPU thread in

	 * vgic_change_active_prepare)  and still has to sync back this IRQ,

	 * so we release and re-acquire the spin_lock to let the other thread

	 * sync back the IRQ.

	 */

	while (irq->vcpu && /* IRQ may have state in an LR somewhere */

	       irq->vcpu != requester_vcpu && /* Current thread is not the VCPU thread */

	       irq->vcpu->cpu != -1) /* VCPU thread is running */

		cond_resched_lock(&irq->irq_lock);