async_pf.c

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/*
 * kvm asynchronous fault support
 *
 * Copyright 2010 Red Hat, Inc.
 *
 * Author:
 *      Gleb Natapov <[email protected]>
 *
 * 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 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)
{
    if (async_pf_cache)
        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 page *page = NULL;
    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();

    use_mm(mm);
    down_read(&mm->mmap_sem);
    get_user_pages(current, mm, addr, 1, 1, 0, &page, NULL);
    up_read(&mm->mmap_sem);
    unuse_mm(mm);

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

    if (waitqueue_active(&vcpu->wq))
        wake_up_interruptible(&vcpu->wq);

    mmdrop(mm);
    kvm_put_kvm(vcpu->kvm);
}

void kvm_clear_async_pf_completion_queue(struct kvm_vcpu *vcpu)
{
    /* cancel outstanding work queue item */
    while (!list_empty(&vcpu->async_pf.queue)) {
        struct kvm_async_pf *work =
            list_entry(vcpu->async_pf.queue.next,
                   typeof(*work), queue);
        cancel_work_sync(&work->work);
        list_del(&work->queue);
        if (!work->done) /* work was canceled */
            kmem_cache_free(async_pf_cache, work);
    }

    spin_lock(&vcpu->async_pf.lock);
    while (!list_empty(&vcpu->async_pf.done)) {
        struct kvm_async_pf *work =
            list_entry(vcpu->async_pf.done.next,
                   typeof(*work), link);
        list_del(&work->link);
        if (!is_error_page(work->page))
            kvm_release_page_clean(work->page);
        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);

        if (work->page)
            kvm_arch_async_page_ready(vcpu, work);
        kvm_arch_async_page_present(vcpu, work);

        list_del(&work->queue);
        vcpu->async_pf.queued--;
        if (!is_error_page(work->page))
            kvm_release_page_clean(work->page);
        kmem_cache_free(async_pf_cache, work);
    }
}

int kvm_setup_async_pf(struct kvm_vcpu *vcpu, gva_t gva, gfn_t gfn,
               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);
    if (!work)
        return 0;

    work->page = NULL;
    work->done = false;
    work->vcpu = vcpu;
    work->gva = gva;
    work->addr = gfn_to_hva(vcpu->kvm, gfn);
    work->arch = *arch;
    work->mm = current->mm;
    atomic_inc(&work->mm->mm_count);
    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);
    mmdrop(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->page = KVM_ERR_PTR_BAD_PAGE;
    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;
}