arch/x86/kvm/page_track.c

   1 /*
   2  * Support KVM gust page tracking
   3  *
   4  * This feature allows us to track page access in guest. Currently, only
   5  * write access is tracked.
   6  *
   7  * Copyright(C) 2015 Intel Corporation.
   8  *
   9  * Author:
  10  *   Xiao Guangrong <guangrong.xiao@linux.intel.com>
  11  *
  12  * This work is licensed under the terms of the GNU GPL, version 2.  See
  13  * the COPYING file in the top-level directory.
  14  */
  15
  16 #include <linux/kvm_host.h>
  17 #include <asm/kvm_host.h>
  18 #include <asm/kvm_page_track.h>
  19
  20 #include "mmu.h"
  21
  22 void kvm_page_track_free_memslot(struct kvm_memory_slot *free,
  23                                  struct kvm_memory_slot *dont)
  24 {
  25         int i;
  26
  27         for (i = 0; i < KVM_PAGE_TRACK_MAX; i++)
  28                 if (!dont || free->arch.gfn_track[i] !=
  29                       dont->arch.gfn_track[i]) {
  30                         kvfree(free->arch.gfn_track[i]);
  31                         free->arch.gfn_track[i] = NULL;
  32                 }
  33 }
  34
  35 int kvm_page_track_create_memslot(struct kvm_memory_slot *slot,
  36                                   unsigned long npages)
  37 {
  38         int  i;
  39
  40         for (i = 0; i < KVM_PAGE_TRACK_MAX; i++) {
  41                 slot->arch.gfn_track[i] = kvm_kvzalloc(npages *
  42                                             sizeof(*slot->arch.gfn_track[i]));
  43                 if (!slot->arch.gfn_track[i])
  44                         goto track_free;
  45         }
  46
  47         return 0;
  48
  49 track_free:
  50         kvm_page_track_free_memslot(slot, NULL);
  51         return -ENOMEM;
  52 }
  53
  54 static inline bool page_track_mode_is_valid(enum kvm_page_track_mode mode)
  55 {
  56         if (mode < 0 || mode >= KVM_PAGE_TRACK_MAX)
  57                 return false;
  58
  59         return true;
  60 }
  61
  62 static void update_gfn_track(struct kvm_memory_slot *slot, gfn_t gfn,
  63                              enum kvm_page_track_mode mode, short count)
  64 {
  65         int index, val;
  66
  67         index = gfn_to_index(gfn, slot->base_gfn, PT_PAGE_TABLE_LEVEL);
  68
  69         val = slot->arch.gfn_track[mode][index];
  70
  71         if (WARN_ON(val + count < 0 || val + count > USHRT_MAX))
  72                 return;
  73
  74         slot->arch.gfn_track[mode][index] += count;
  75 }
  76
  77 /*
  78  * add guest page to the tracking pool so that corresponding access on that
  79  * page will be intercepted.
  80  *
  81  * It should be called under the protection both of mmu-lock and kvm->srcu
  82  * or kvm->slots_lock.
  83  *
  84  * @kvm: the guest instance we are interested in.
  85  * @slot: the @gfn belongs to.
  86  * @gfn: the guest page.
  87  * @mode: tracking mode, currently only write track is supported.
  88  */
  89 void kvm_slot_page_track_add_page(struct kvm *kvm,
  90                                   struct kvm_memory_slot *slot, gfn_t gfn,
  91                                   enum kvm_page_track_mode mode)
  92 {
  93
  94         if (WARN_ON(!page_track_mode_is_valid(mode)))
  95                 return;
  96
  97         update_gfn_track(slot, gfn, mode, 1);
  98
  99         /*
 100          * new track stops large page mapping for the
 101          * tracked page.
 102          */
 103         kvm_mmu_gfn_disallow_lpage(slot, gfn);
 104
 105         if (mode == KVM_PAGE_TRACK_WRITE)
 106                 if (kvm_mmu_slot_gfn_write_protect(kvm, slot, gfn))
 107                         kvm_flush_remote_tlbs(kvm);
 108 }
 109
 110 /*
 111  * remove the guest page from the tracking pool which stops the interception
 112  * of corresponding access on that page. It is the opposed operation of
 113  * kvm_slot_page_track_add_page().
 114  *
 115  * It should be called under the protection both of mmu-lock and kvm->srcu
 116  * or kvm->slots_lock.
 117  *
 118  * @kvm: the guest instance we are interested in.
 119  * @slot: the @gfn belongs to.
 120  * @gfn: the guest page.
 121  * @mode: tracking mode, currently only write track is supported.
 122  */
 123 void kvm_slot_page_track_remove_page(struct kvm *kvm,
 124                                      struct kvm_memory_slot *slot, gfn_t gfn,
 125                                      enum kvm_page_track_mode mode)
 126 {
 127         if (WARN_ON(!page_track_mode_is_valid(mode)))
 128                 return;
 129
 130         update_gfn_track(slot, gfn, mode, -1);
 131
 132         /*
 133          * allow large page mapping for the tracked page
 134          * after the tracker is gone.
 135          */
 136         kvm_mmu_gfn_allow_lpage(slot, gfn);
 137 }
 138
 139 /*
 140  * check if the corresponding access on the specified guest page is tracked.
 141  */
 142 bool kvm_page_track_is_active(struct kvm_vcpu *vcpu, gfn_t gfn,
 143                               enum kvm_page_track_mode mode)
 144 {
 145         struct kvm_memory_slot *slot;
 146         int index;
 147
 148         if (WARN_ON(!page_track_mode_is_valid(mode)))
 149                 return false;
 150
 151         slot = kvm_vcpu_gfn_to_memslot(vcpu, gfn);
 152         if (!slot)
 153                 return false;
 154
 155         index = gfn_to_index(gfn, slot->base_gfn, PT_PAGE_TABLE_LEVEL);
 156         return !!ACCESS_ONCE(slot->arch.gfn_track[mode][index]);
 157 }
 158
 159 void kvm_page_track_init(struct kvm *kvm)
 160 {
 161         struct kvm_page_track_notifier_head *head;
 162
 163         head = &kvm->arch.track_notifier_head;
 164         init_srcu_struct(&head->track_srcu);
 165         INIT_HLIST_HEAD(&head->track_notifier_list);
 166 }
 167
 168 /*
 169  * register the notifier so that event interception for the tracked guest
 170  * pages can be received.
 171  */
 172 void
 173 kvm_page_track_register_notifier(struct kvm *kvm,
 174                                  struct kvm_page_track_notifier_node *n)
 175 {
 176         struct kvm_page_track_notifier_head *head;
 177
 178         head = &kvm->arch.track_notifier_head;
 179
 180         spin_lock(&kvm->mmu_lock);
 181         hlist_add_head_rcu(&n->node, &head->track_notifier_list);
 182         spin_unlock(&kvm->mmu_lock);
 183 }
 184
 185 /*
 186  * stop receiving the event interception. It is the opposed operation of
 187  * kvm_page_track_register_notifier().
 188  */
 189 void
 190 kvm_page_track_unregister_notifier(struct kvm *kvm,
 191                                    struct kvm_page_track_notifier_node *n)
 192 {
 193         struct kvm_page_track_notifier_head *head;
 194
 195         head = &kvm->arch.track_notifier_head;
 196
 197         spin_lock(&kvm->mmu_lock);
 198         hlist_del_rcu(&n->node);
 199         spin_unlock(&kvm->mmu_lock);
 200         synchronize_srcu(&head->track_srcu);
 201 }
 202
 203 /*
 204  * Notify the node that write access is intercepted and write emulation is
 205  * finished at this time.
 206  *
 207  * The node should figure out if the written page is the one that node is
 208  * interested in by itself.
 209  */
 210 void kvm_page_track_write(struct kvm_vcpu *vcpu, gpa_t gpa, const u8 *new,
 211                           int bytes)
 212 {
 213         struct kvm_page_track_notifier_head *head;
 214         struct kvm_page_track_notifier_node *n;
 215         int idx;
 216
 217         head = &vcpu->kvm->arch.track_notifier_head;
 218
 219         if (hlist_empty(&head->track_notifier_list))
 220                 return;
 221
 222         idx = srcu_read_lock(&head->track_srcu);
 223         hlist_for_each_entry_rcu(n, &head->track_notifier_list, node)
 224                 if (n->track_write)
 225                         n->track_write(vcpu, gpa, new, bytes);
 226         srcu_read_unlock(&head->track_srcu, idx);
 227 }