page_track.c

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// SPDX-License-Identifier: GPL-2.0-only
/*
 * Support KVM gust page tracking
 *
 * This feature allows us to track page access in guest. Currently, only
 * write access is tracked.
 *
 * Copyright(C) 2015 Intel Corporation.
 *
 * Author:
 *   Xiao Guangrong <guangrong.xiao@linux.intel.com>
 */
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
#include <linux/lockdep.h>
#include <linux/kvm_host.h>
#include <linux/rculist.h>
 
#include "mmu.h"
#include "mmu_internal.h"
#include "page_track.h"
 
bool kvm_page_track_write_tracking_enabled(struct kvm *kvm)
{
    return IS_ENABLED(CONFIG_KVM_EXTERNAL_WRITE_TRACKING) ||
           !tdp_enabled || kvm_shadow_root_allocated(kvm);
}
 
void kvm_page_track_free_memslot(struct kvm_memory_slot *slot)
{
    kvfree(slot->arch.gfn_write_track);
    slot->arch.gfn_write_track = NULL;
}
 
static int __kvm_page_track_write_tracking_alloc(struct kvm_memory_slot *slot,
                         unsigned long npages)
{
    const size_t size = sizeof(*slot->arch.gfn_write_track);
 
    if (!slot->arch.gfn_write_track)
        slot->arch.gfn_write_track = __vcalloc(npages, size,
                               GFP_KERNEL_ACCOUNT);
 
    return slot->arch.gfn_write_track ? 0 : -ENOMEM;
}
 
int kvm_page_track_create_memslot(struct kvm *kvm,
                  struct kvm_memory_slot *slot,
                  unsigned long npages)
{
    if (!kvm_page_track_write_tracking_enabled(kvm))
        return 0;
 
    return __kvm_page_track_write_tracking_alloc(slot, npages);
}
 
int kvm_page_track_write_tracking_alloc(struct kvm_memory_slot *slot)
{
    return __kvm_page_track_write_tracking_alloc(slot, slot->npages);
}
 
static void update_gfn_write_track(struct kvm_memory_slot *slot, gfn_t gfn,
                   short count)
{
    int index, val;
 
    index = gfn_to_index(gfn, slot->base_gfn, PG_LEVEL_4K);
 
    val = slot->arch.gfn_write_track[index];
 
    if (WARN_ON_ONCE(val + count < 0 || val + count > USHRT_MAX))
        return;
 
    slot->arch.gfn_write_track[index] += count;
}
 
void __kvm_write_track_add_gfn(struct kvm *kvm, struct kvm_memory_slot *slot,
                   gfn_t gfn)
{
    lockdep_assert_held_write(&kvm->mmu_lock);
 
    lockdep_assert_once(lockdep_is_held(&kvm->slots_lock) ||
                srcu_read_lock_held(&kvm->srcu));
 
    if (KVM_BUG_ON(!kvm_page_track_write_tracking_enabled(kvm), kvm))
        return;
 
    update_gfn_write_track(slot, gfn, 1);
 
    /*
     * new track stops large page mapping for the
     * tracked page.
     */
    kvm_mmu_gfn_disallow_lpage(slot, gfn);
 
    if (kvm_mmu_slot_gfn_write_protect(kvm, slot, gfn, PG_LEVEL_4K))
        kvm_flush_remote_tlbs(kvm);
}
 
void __kvm_write_track_remove_gfn(struct kvm *kvm,
                  struct kvm_memory_slot *slot, gfn_t gfn)
{
    lockdep_assert_held_write(&kvm->mmu_lock);
 
    lockdep_assert_once(lockdep_is_held(&kvm->slots_lock) ||
                srcu_read_lock_held(&kvm->srcu));
 
    if (KVM_BUG_ON(!kvm_page_track_write_tracking_enabled(kvm), kvm))
        return;
 
    update_gfn_write_track(slot, gfn, -1);
 
    /*
     * allow large page mapping for the tracked page
     * after the tracker is gone.
     */
    kvm_mmu_gfn_allow_lpage(slot, gfn);
}
 
/*
 * check if the corresponding access on the specified guest page is tracked.
 */
bool kvm_gfn_is_write_tracked(struct kvm *kvm,
                  const struct kvm_memory_slot *slot, gfn_t gfn)
{
    int index;
 
    if (!slot)
        return false;
 
    if (!kvm_page_track_write_tracking_enabled(kvm))
        return false;
 
    index = gfn_to_index(gfn, slot->base_gfn, PG_LEVEL_4K);
    return !!READ_ONCE(slot->arch.gfn_write_track[index]);
}
 
#ifdef CONFIG_KVM_EXTERNAL_WRITE_TRACKING
void kvm_page_track_cleanup(struct kvm *kvm)
{
    struct kvm_page_track_notifier_head *head;
 
    head = &kvm->arch.track_notifier_head;
    cleanup_srcu_struct(&head->track_srcu);
}
 
int kvm_page_track_init(struct kvm *kvm)
{
    struct kvm_page_track_notifier_head *head;
 
    head = &kvm->arch.track_notifier_head;
    INIT_HLIST_HEAD(&head->track_notifier_list);
    return init_srcu_struct(&head->track_srcu);
}
 
/*
 * register the notifier so that event interception for the tracked guest
 * pages can be received.
 */
int kvm_page_track_register_notifier(struct kvm *kvm,
                     struct kvm_page_track_notifier_node *n)
{
    struct kvm_page_track_notifier_head *head;
 
    if (!kvm || kvm->mm != current->mm)
        return -ESRCH;
 
    kvm_get_kvm(kvm);
 
    head = &kvm->arch.track_notifier_head;
 
    write_lock(&kvm->mmu_lock);
    hlist_add_head_rcu(&n->node, &head->track_notifier_list);
    write_unlock(&kvm->mmu_lock);
    return 0;
}
EXPORT_SYMBOL_GPL(kvm_page_track_register_notifier);
 
/*
 * stop receiving the event interception. It is the opposed operation of
 * kvm_page_track_register_notifier().
 */
void kvm_page_track_unregister_notifier(struct kvm *kvm,
                    struct kvm_page_track_notifier_node *n)
{
    struct kvm_page_track_notifier_head *head;
 
    head = &kvm->arch.track_notifier_head;
 
    write_lock(&kvm->mmu_lock);
    hlist_del_rcu(&n->node);
    write_unlock(&kvm->mmu_lock);
    synchronize_srcu(&head->track_srcu);
 
    kvm_put_kvm(kvm);
}
EXPORT_SYMBOL_GPL(kvm_page_track_unregister_notifier);
 
/*
 * Notify the node that write access is intercepted and write emulation is
 * finished at this time.
 *
 * The node should figure out if the written page is the one that node is
 * interested in by itself.
 */
void __kvm_page_track_write(struct kvm *kvm, gpa_t gpa, const u8 *new, int bytes)
{
    struct kvm_page_track_notifier_head *head;
    struct kvm_page_track_notifier_node *n;
    int idx;
 
    head = &kvm->arch.track_notifier_head;
 
    if (hlist_empty(&head->track_notifier_list))
        return;
 
    idx = srcu_read_lock(&head->track_srcu);
    hlist_for_each_entry_srcu(n, &head->track_notifier_list, node,
                  srcu_read_lock_held(&head->track_srcu))
        if (n->track_write)
            n->track_write(gpa, new, bytes, n);
    srcu_read_unlock(&head->track_srcu, idx);
}
 
/*
 * Notify external page track nodes that a memory region is being removed from
 * the VM, e.g. so that users can free any associated metadata.
 */
void kvm_page_track_delete_slot(struct kvm *kvm, struct kvm_memory_slot *slot)
{
    struct kvm_page_track_notifier_head *head;
    struct kvm_page_track_notifier_node *n;
    int idx;
 
    head = &kvm->arch.track_notifier_head;
 
    if (hlist_empty(&head->track_notifier_list))
        return;
 
    idx = srcu_read_lock(&head->track_srcu);
    hlist_for_each_entry_srcu(n, &head->track_notifier_list, node,
                  srcu_read_lock_held(&head->track_srcu))
        if (n->track_remove_region)
            n->track_remove_region(slot->base_gfn, slot->npages, n);
    srcu_read_unlock(&head->track_srcu, idx);
}
 
/*
 * add guest page to the tracking pool so that corresponding access on that
 * page will be intercepted.
 *
 * @kvm: the guest instance we are interested in.
 * @gfn: the guest page.
 */
int kvm_write_track_add_gfn(struct kvm *kvm, gfn_t gfn)
{
    struct kvm_memory_slot *slot;
    int idx;
 
    idx = srcu_read_lock(&kvm->srcu);
 
    slot = gfn_to_memslot(kvm, gfn);
    if (!slot) {
        srcu_read_unlock(&kvm->srcu, idx);
        return -EINVAL;
    }
 
    write_lock(&kvm->mmu_lock);
    __kvm_write_track_add_gfn(kvm, slot, gfn);
    write_unlock(&kvm->mmu_lock);
 
    srcu_read_unlock(&kvm->srcu, idx);
 
    return 0;
}
EXPORT_SYMBOL_GPL(kvm_write_track_add_gfn);
 
/*
 * remove the guest page from the tracking pool which stops the interception
 * of corresponding access on that page.
 *
 * @kvm: the guest instance we are interested in.
 * @gfn: the guest page.
 */
int kvm_write_track_remove_gfn(struct kvm *kvm, gfn_t gfn)
{
    struct kvm_memory_slot *slot;
    int idx;
 
    idx = srcu_read_lock(&kvm->srcu);
 
    slot = gfn_to_memslot(kvm, gfn);
    if (!slot) {
        srcu_read_unlock(&kvm->srcu, idx);
        return -EINVAL;
    }
 
    write_lock(&kvm->mmu_lock);
    __kvm_write_track_remove_gfn(kvm, slot, gfn);
    write_unlock(&kvm->mmu_lock);
 
    srcu_read_unlock(&kvm->srcu, idx);
 
    return 0;
}
EXPORT_SYMBOL_GPL(kvm_write_track_remove_gfn);
#endif