async_pf.c

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// SPDX-License-Identifier: GPL-2.0-only
/*
 * kvm asynchronous fault support
 *
 * Copyright 2010 Red Hat, Inc.
 *
 * Author:
 *      Gleb Natapov <gleb@redhat.com>
 */
 
#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 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;
    gpa_t cr2_or_gpa = apf->cr2_or_gpa;
    int locked = 1;
    bool first;
 
    might_sleep();
 
    /*
     * This work is run asynchronously to the task which owns
     * mm and might be done in another context, so we must
     * access remotely.
     */
    mmap_read_lock(mm);
    get_user_pages_remote(mm, addr, 1, FOLL_WRITE, NULL, &locked);
    if (locked)
        mmap_read_unlock(mm);
 
    if (IS_ENABLED(CONFIG_KVM_ASYNC_PF_SYNC))
        kvm_arch_async_page_present(vcpu, apf);
 
    spin_lock(&vcpu->async_pf.lock);
    first = list_empty(&vcpu->async_pf.done);
    list_add_tail(&apf->link, &vcpu->async_pf.done);
    apf->vcpu = NULL;
    spin_unlock(&vcpu->async_pf.lock);
 
    if (!IS_ENABLED(CONFIG_KVM_ASYNC_PF_SYNC) && first)
        kvm_arch_async_page_present_queued(vcpu);
 
    /*
     * apf may be freed by kvm_check_async_pf_completion() after
     * this point
     */
 
    trace_kvm_async_pf_completed(addr, cr2_or_gpa);
 
    __kvm_vcpu_wake_up(vcpu);
 
    mmput(mm);
}
 
static void kvm_flush_and_free_async_pf_work(struct kvm_async_pf *work)
{
    /*
     * The async #PF is "done", but KVM must wait for the work item itself,
     * i.e. async_pf_execute(), to run to completion.  If KVM is a module,
     * KVM must ensure *no* code owned by the KVM (the module) can be run
     * after the last call to module_put().  Note, flushing the work item
     * is always required when the item is taken off the completion queue.
     * E.g. even if the vCPU handles the item in the "normal" path, the VM
     * could be terminated before async_pf_execute() completes.
     *
     * Wake all events skip the queue and go straight done, i.e. don't
     * need to be flushed (but sanity check that the work wasn't queued).
     */
    if (work->wakeup_all)
        WARN_ON_ONCE(work->work.func);
    else
        flush_work(&work->work);
    kmem_cache_free(async_pf_cache, work);
}
 
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);
            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);
 
        spin_unlock(&vcpu->async_pf.lock);
        kvm_flush_and_free_async_pf_work(work);
        spin_lock(&vcpu->async_pf.lock);
    }
    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_dequeue_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);
        if (!IS_ENABLED(CONFIG_KVM_ASYNC_PF_SYNC))
            kvm_arch_async_page_present(vcpu, work);
 
        list_del(&work->queue);
        vcpu->async_pf.queued--;
        kvm_flush_and_free_async_pf_work(work);
    }
}
 
/*
 * Try to schedule a job to handle page fault asynchronously. Returns 'true' on
 * success, 'false' on failure (page fault has to be handled synchronously).
 */
bool kvm_setup_async_pf(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
            unsigned long hva, struct kvm_arch_async_pf *arch)
{
    struct kvm_async_pf *work;
 
    if (vcpu->async_pf.queued >= ASYNC_PF_PER_VCPU)
        return false;
 
    /* Arch specific code should not do async PF in this case */
    if (unlikely(kvm_is_error_hva(hva)))
        return false;
 
    /*
     * 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 false;
 
    work->wakeup_all = false;
    work->vcpu = vcpu;
    work->cr2_or_gpa = cr2_or_gpa;
    work->addr = hva;
    work->arch = *arch;
    work->mm = current->mm;
    mmget(work->mm);
 
    INIT_WORK(&work->work, async_pf_execute);
 
    list_add_tail(&work->queue, &vcpu->async_pf.queue);
    vcpu->async_pf.queued++;
    work->notpresent_injected = kvm_arch_async_page_not_present(vcpu, work);
 
    schedule_work(&work->work);
 
    return true;
}
 
int kvm_async_pf_wakeup_all(struct kvm_vcpu *vcpu)
{
    struct kvm_async_pf *work;
    bool first;
 
    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);
    first = list_empty(&vcpu->async_pf.done);
    list_add_tail(&work->link, &vcpu->async_pf.done);
    spin_unlock(&vcpu->async_pf.lock);
 
    if (!IS_ENABLED(CONFIG_KVM_ASYNC_PF_SYNC) && first)
        kvm_arch_async_page_present_queued(vcpu);
 
    vcpu->async_pf.queued++;
    return 0;
}