static int evtchn_set_fn(struct kvm_kernel_irq_routing_entry *e, struct kvm *kvm,
			 int irq_source_id, int level, bool line_status)
{
	bool mm_borrowed = false;
	int rc;

	if (!level)
		return -1;

	rc = kvm_xen_set_evtchn_fast(e, kvm);
	if (rc != -EWOULDBLOCK)
		return rc;

	if (current->mm != kvm->mm) {
		/*
		 * If not on a thread which already belongs to this KVM,
		 * we'd better be in the irqfd workqueue.
		 */
		if (WARN_ON_ONCE(current->mm))
			return -EINVAL;

		kthread_use_mm(kvm->mm);
		mm_borrowed = true;
	}

	/*
	 * For the irqfd workqueue, using the main kvm->lock mutex is
	 * fine since this function is invoked from kvm_set_irq() with
	 * no other lock held, no srcu. In future if it will be called
	 * directly from a vCPU thread (e.g. on hypercall for an IPI)
	 * then it may need to switch to using a leaf-node mutex for
	 * serializing the shared_info mapping.
	 */
	mutex_lock(&kvm->lock);

	/*
	 * It is theoretically possible for the page to be unmapped
	 * and the MMU notifier to invalidate the shared_info before
	 * we even get to use it. In that case, this looks like an
	 * infinite loop. It was tempting to do it via the userspace
	 * HVA instead... but that just *hides* the fact that it's
	 * an infinite loop, because if a fault occurs and it waits
	 * for the page to come back, it can *still* immediately
	 * fault and have to wait again, repeatedly.
	 *
	 * Conversely, the page could also have been reinstated by
	 * another thread before we even obtain the mutex above, so
	 * check again *first* before remapping it.
	 */
	do {
		struct gfn_to_pfn_cache *gpc = &kvm->arch.xen.shinfo_cache;
		int idx;

		rc = kvm_xen_set_evtchn_fast(e, kvm);
		if (rc != -EWOULDBLOCK)
			break;

		idx = srcu_read_lock(&kvm->srcu);
		rc = kvm_gfn_to_pfn_cache_refresh(kvm, gpc, gpc->gpa,
						  PAGE_SIZE, false);
		srcu_read_unlock(&kvm->srcu, idx);
	} while(!rc);

	mutex_unlock(&kvm->lock);

	if (mm_borrowed)
		kthread_unuse_mm(kvm->mm);

	return rc;
}
static int evtchn_set_fn(struct kvm_kernel_irq_routing_entry *e, struct kvm *kvm,
			 int irq_source_id, int level, bool line_status)
{
	bool mm_borrowed = false;
	int rc;

	if (!level)
		return -1;

	rc = kvm_xen_set_evtchn_fast(e, kvm);
	if (rc != -EWOULDBLOCK)
		return rc;

	if (current->mm != kvm->mm) {
		 
		if (WARN_ON_ONCE(current->mm))
			return -EINVAL;

		kthread_use_mm(kvm->mm);
		mm_borrowed = true;
	}

	 
	mutex_lock(&kvm->lock);

	 
	do {
		struct gfn_to_pfn_cache *gpc = &kvm->arch.xen.shinfo_cache;
		int idx;

		rc = kvm_xen_set_evtchn_fast(e, kvm);
		if (rc != -EWOULDBLOCK)
			break;

		idx = srcu_read_lock(&kvm->srcu);
		rc = kvm_gfn_to_pfn_cache_refresh(kvm, gpc, gpc->gpa,
						  PAGE_SIZE, false);
		srcu_read_unlock(&kvm->srcu, idx);
	} while(!rc);

	mutex_unlock(&kvm->lock);

	if (mm_borrowed)
		kthread_unuse_mm(kvm->mm);

	return rc;
}