// 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 kvm_vcpu *vcpu = apf->vcpu;
        struct mm_struct *mm = vcpu->kvm->mm;
        unsigned long addr = apf->addr;
        gpa_t cr2_or_gpa = apf->cr2_or_gpa;
        int locked = 1;
        bool first;

        might_sleep();

        /*
         * Attempt to pin the VM's host address space, and simply skip gup() if
         * acquiring a pin fail, i.e. if the process is exiting.  Note, KVM
         * holds a reference to its associated mm_struct until the very end of
         * kvm_destroy_vm(), i.e. the struct itself won't be freed before this
         * work item is fully processed.
         */
        if (mmget_not_zero(mm)) {
                mmap_read_lock(mm);
                get_user_pages_remote(mm, addr, 1, FOLL_WRITE, NULL, &locked);
                if (locked)
                        mmap_read_unlock(mm);
                mmput(mm);
        }

        /*
         * Notify and kick the vCPU even if faulting in the page failed, e.g.
         * so that the vCPU can retry the fault synchronously.
         */
        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);
        spin_unlock(&vcpu->async_pf.lock);

        /*
         * The apf struct may be freed by kvm_check_async_pf_completion() as
         * soon as the lock is dropped.  Nullify it to prevent improper usage.
         */
        apf = NULL;

        if (!IS_ENABLED(CONFIG_KVM_ASYNC_PF_SYNC) && first)
                kvm_arch_async_page_present_queued(vcpu);

        trace_kvm_async_pf_completed(addr, cr2_or_gpa);

        __kvm_vcpu_wake_up(vcpu);
}

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)
{
        /* 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);

#ifdef CONFIG_KVM_ASYNC_PF_SYNC
                flush_work(&work->work);
#else
                if (cancel_work_sync(&work->work))
                        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);
        if (!work)
                return false;

        work->wakeup_all = false;
        work->vcpu = vcpu;
        work->cr2_or_gpa = cr2_or_gpa;
        work->addr = hva;
        work->arch = *arch;

        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;
}