/*
   * kvm asynchronous fault support
   *
   * Copyright 2010 Red Hat, Inc.
   *
   * Author:
   *      Gleb Natapov <gleb@redhat.com>
   *
   * This file is free software; you can redistribute it and/or modify
   * it under the terms of version 2 of the GNU General Public License
   * as published by the Free Software Foundation.
   *
   * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU General Public License for more details.
   *
   * You should have received a copy of the GNU General Public License
   * along with this program; if not, write to the Free Software Foundation,
   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA.
   */
  
  #include <linux/kvm_host.h>
  #include <linux/slab.h>
  #include <linux/module.h>
  #include <linux/mmu_context.h>
  
  #include "async_pf.h"
  #include <trace/events/kvm.h>

  static inline void kvm_async_page_present_sync(struct kvm_vcpu *vcpu,
  					       struct kvm_async_pf *work)
  {
  #ifdef CONFIG_KVM_ASYNC_PF_SYNC
  	kvm_arch_async_page_present(vcpu, work);
  #endif
  }
  static inline void kvm_async_page_present_async(struct kvm_vcpu *vcpu,
  						struct kvm_async_pf *work)
  {
  #ifndef CONFIG_KVM_ASYNC_PF_SYNC
  	kvm_arch_async_page_present(vcpu, work);
  #endif
  }

  static struct kmem_cache *async_pf_cache;
  
  int kvm_async_pf_init(void)
  {
  	async_pf_cache = KMEM_CACHE(kvm_async_pf, 0);
  
  	if (!async_pf_cache)
  		return -ENOMEM;
  
  	return 0;
  }
  
  void kvm_async_pf_deinit(void)
  {

  	kmem_cache_destroy(async_pf_cache);

  	async_pf_cache = NULL;
  }
  
  void kvm_async_pf_vcpu_init(struct kvm_vcpu *vcpu)
  {
  	INIT_LIST_HEAD(&vcpu->async_pf.done);
  	INIT_LIST_HEAD(&vcpu->async_pf.queue);
  	spin_lock_init(&vcpu->async_pf.lock);
  }
  
  static void async_pf_execute(struct work_struct *work)
  {

  	struct kvm_async_pf *apf =
  		container_of(work, struct kvm_async_pf, work);
  	struct mm_struct *mm = apf->mm;
  	struct kvm_vcpu *vcpu = apf->vcpu;
  	unsigned long addr = apf->addr;
  	gva_t gva = apf->gva;
  
  	might_sleep();

  	/*
  	 * This work is run asynchromously to the task which owns
  	 * mm and might be done in another context, so we must
  	 * use FOLL_REMOTE.
  	 */

  	__get_user_pages_unlocked(NULL, mm, addr, 1, NULL,
  			FOLL_WRITE | FOLL_REMOTE);

  	kvm_async_page_present_sync(vcpu, apf);

  
  	spin_lock(&vcpu->async_pf.lock);
  	list_add_tail(&apf->link, &vcpu->async_pf.done);

  	apf->vcpu = NULL;

  	spin_unlock(&vcpu->async_pf.lock);
  
  	/*
  	 * apf may be freed by kvm_check_async_pf_completion() after
  	 * this point
  	 */

  	trace_kvm_async_pf_completed(addr, gva);

  	/*
  	 * This memory barrier pairs with prepare_to_wait's set_current_state()
  	 */
  	smp_mb();

  	if (swait_active(&vcpu->wq))
  		swake_up(&vcpu->wq);

  	mmput(mm);

  	kvm_put_kvm(vcpu->kvm);
  }
  
  void kvm_clear_async_pf_completion_queue(struct kvm_vcpu *vcpu)
  {

  	spin_lock(&vcpu->async_pf.lock);

  	/* cancel outstanding work queue item */
  	while (!list_empty(&vcpu->async_pf.queue)) {
  		struct kvm_async_pf *work =

  			list_first_entry(&vcpu->async_pf.queue,
  					 typeof(*work), queue);

  		list_del(&work->queue);

  		/*
  		 * We know it's present in vcpu->async_pf.done, do
  		 * nothing here.
  		 */
  		if (!work->vcpu)
  			continue;
  
  		spin_unlock(&vcpu->async_pf.lock);

  #ifdef CONFIG_KVM_ASYNC_PF_SYNC
  		flush_work(&work->work);
  #else

  		if (cancel_work_sync(&work->work)) {

  			mmput(work->mm);

  			kvm_put_kvm(vcpu->kvm); /* == work->vcpu->kvm */

  			kmem_cache_free(async_pf_cache, work);

  		}

  #endif

  		spin_lock(&vcpu->async_pf.lock);

  	}

  	while (!list_empty(&vcpu->async_pf.done)) {
  		struct kvm_async_pf *work =

  			list_first_entry(&vcpu->async_pf.done,
  					 typeof(*work), link);

  		list_del(&work->link);

  		kmem_cache_free(async_pf_cache, work);
  	}
  	spin_unlock(&vcpu->async_pf.lock);
  
  	vcpu->async_pf.queued = 0;
  }
  
  void kvm_check_async_pf_completion(struct kvm_vcpu *vcpu)
  {
  	struct kvm_async_pf *work;

  	while (!list_empty_careful(&vcpu->async_pf.done) &&
  	      kvm_arch_can_inject_async_page_present(vcpu)) {
  		spin_lock(&vcpu->async_pf.lock);
  		work = list_first_entry(&vcpu->async_pf.done, typeof(*work),
  					      link);
  		list_del(&work->link);
  		spin_unlock(&vcpu->async_pf.lock);

  		kvm_arch_async_page_ready(vcpu, work);

  		kvm_async_page_present_async(vcpu, work);

  		list_del(&work->queue);
  		vcpu->async_pf.queued--;

  		kmem_cache_free(async_pf_cache, work);
  	}

  }

  int kvm_setup_async_pf(struct kvm_vcpu *vcpu, gva_t gva, unsigned long hva,

  		       struct kvm_arch_async_pf *arch)
  {
  	struct kvm_async_pf *work;
  
  	if (vcpu->async_pf.queued >= ASYNC_PF_PER_VCPU)
  		return 0;
  
  	/* setup delayed work */
  
  	/*
  	 * do alloc nowait since if we are going to sleep anyway we
  	 * may as well sleep faulting in page
  	 */

  	work = kmem_cache_zalloc(async_pf_cache, GFP_NOWAIT | __GFP_NOWARN);

  	if (!work)
  		return 0;

  	work->wakeup_all = false;

  	work->vcpu = vcpu;
  	work->gva = gva;

  	work->addr = hva;

  	work->arch = *arch;
  	work->mm = current->mm;

  	atomic_inc(&work->mm->mm_users);

  	kvm_get_kvm(work->vcpu->kvm);
  
  	/* this can't really happen otherwise gfn_to_pfn_async
  	   would succeed */
  	if (unlikely(kvm_is_error_hva(work->addr)))
  		goto retry_sync;
  
  	INIT_WORK(&work->work, async_pf_execute);
  	if (!schedule_work(&work->work))
  		goto retry_sync;
  
  	list_add_tail(&work->queue, &vcpu->async_pf.queue);
  	vcpu->async_pf.queued++;
  	kvm_arch_async_page_not_present(vcpu, work);
  	return 1;
  retry_sync:
  	kvm_put_kvm(work->vcpu->kvm);

  	mmput(work->mm);

  	kmem_cache_free(async_pf_cache, work);
  	return 0;
  }

  
  int kvm_async_pf_wakeup_all(struct kvm_vcpu *vcpu)
  {
  	struct kvm_async_pf *work;

  	if (!list_empty_careful(&vcpu->async_pf.done))

  		return 0;
  
  	work = kmem_cache_zalloc(async_pf_cache, GFP_ATOMIC);
  	if (!work)
  		return -ENOMEM;

  	work->wakeup_all = true;

  	INIT_LIST_HEAD(&work->queue); /* for list_del to work */

  	spin_lock(&vcpu->async_pf.lock);

  	list_add_tail(&work->link, &vcpu->async_pf.done);

  	spin_unlock(&vcpu->async_pf.lock);

  	vcpu->async_pf.queued++;
  	return 0;
  }