/*
 * 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 <linux/sched/mm.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;
        int locked = 1;

        might_sleep();

        /*
         * This work is run asynchromously to the task which owns
         * mm and might be done in another context, so we must
         * access remotely.
         */
        down_read(&mm->mmap_sem);
        get_user_pages_remote(NULL, mm, addr, 1, FOLL_WRITE, NULL, NULL,
                        &locked);
        if (locked)
                up_read(&mm->mmap_sem);

        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;
        mmget(work->mm);
        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;
}