1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * Support KVM gust page tracking
4 *
5 * This feature allows us to track page access in guest. Currently, only
6 * write access is tracked.
7 *
8 * Copyright(C) 2015 Intel Corporation.
9 *
10 * Author:
11 * Xiao Guangrong <guangrong.xiao@linux.intel.com>
12 */
13 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
14
15 #include <linux/lockdep.h>
16 #include <linux/kvm_host.h>
17 #include <linux/rculist.h>
18
19 #include "mmu.h"
20 #include "mmu_internal.h"
21 #include "page_track.h"
22
23 static bool kvm_external_write_tracking_enabled(struct kvm *kvm)
24 {
25 #ifdef CONFIG_KVM_EXTERNAL_WRITE_TRACKING
26 /*
27 * Read external_write_tracking_enabled before related pointers. Pairs
28 * with the smp_store_release in kvm_page_track_write_tracking_enable().
29 */
30 return smp_load_acquire(&kvm->arch.external_write_tracking_enabled);
31 #else
32 return false;
33 #endif
34 }
35
36 bool kvm_page_track_write_tracking_enabled(struct kvm *kvm)
37 {
38 return kvm_external_write_tracking_enabled(kvm) ||
39 kvm_shadow_root_allocated(kvm) || !tdp_enabled;
40 }
41
42 void kvm_page_track_free_memslot(struct kvm_memory_slot *slot)
43 {
44 vfree(slot->arch.gfn_write_track);
45 slot->arch.gfn_write_track = NULL;
46 }
47
48 static int __kvm_page_track_write_tracking_alloc(struct kvm_memory_slot *slot,
49 unsigned long npages)
50 {
51 const size_t size = sizeof(*slot->arch.gfn_write_track);
52
53 if (!slot->arch.gfn_write_track)
54 slot->arch.gfn_write_track = __vcalloc(npages, size,
55 GFP_KERNEL_ACCOUNT);
56
57 return slot->arch.gfn_write_track ? 0 : -ENOMEM;
58 }
59
60 int kvm_page_track_create_memslot(struct kvm *kvm,
61 struct kvm_memory_slot *slot,
62 unsigned long npages)
63 {
64 if (!kvm_page_track_write_tracking_enabled(kvm))
65 return 0;
66
67 return __kvm_page_track_write_tracking_alloc(slot, npages);
68 }
69
70 int kvm_page_track_write_tracking_alloc(struct kvm_memory_slot *slot)
71 {
72 return __kvm_page_track_write_tracking_alloc(slot, slot->npages);
73 }
74
75 static void update_gfn_write_track(struct kvm_memory_slot *slot, gfn_t gfn,
76 short count)
77 {
78 int index, val;
79
80 index = gfn_to_index(gfn, slot->base_gfn, PG_LEVEL_4K);
81
82 val = slot->arch.gfn_write_track[index];
83
84 if (WARN_ON_ONCE(val + count < 0 || val + count > USHRT_MAX))
85 return;
86
87 slot->arch.gfn_write_track[index] += count;
88 }
89
90 void __kvm_write_track_add_gfn(struct kvm *kvm, struct kvm_memory_slot *slot,
91 gfn_t gfn)
92 {
93 lockdep_assert_held_write(&kvm->mmu_lock);
94
95 lockdep_assert_once(lockdep_is_held(&kvm->slots_lock) ||
96 srcu_read_lock_held(&kvm->srcu));
97
98 if (KVM_BUG_ON(!kvm_page_track_write_tracking_enabled(kvm), kvm))
99 return;
100
101 update_gfn_write_track(slot, gfn, 1);
102
103 /*
104 * new track stops large page mapping for the
105 * tracked page.
106 */
107 kvm_mmu_gfn_disallow_lpage(slot, gfn);
108
109 if (kvm_mmu_slot_gfn_write_protect(kvm, slot, gfn, PG_LEVEL_4K))
110 kvm_flush_remote_tlbs(kvm);
111 }
112
113 void __kvm_write_track_remove_gfn(struct kvm *kvm,
114 struct kvm_memory_slot *slot, gfn_t gfn)
115 {
116 lockdep_assert_held_write(&kvm->mmu_lock);
117
118 lockdep_assert_once(lockdep_is_held(&kvm->slots_lock) ||
119 srcu_read_lock_held(&kvm->srcu));
120
121 if (KVM_BUG_ON(!kvm_page_track_write_tracking_enabled(kvm), kvm))
122 return;
123
124 update_gfn_write_track(slot, gfn, -1);
125
126 /*
127 * allow large page mapping for the tracked page
128 * after the tracker is gone.
129 */
130 kvm_mmu_gfn_allow_lpage(slot, gfn);
131 }
132
133 /*
134 * check if the corresponding access on the specified guest page is tracked.
135 */
136 bool kvm_gfn_is_write_tracked(struct kvm *kvm,
137 const struct kvm_memory_slot *slot, gfn_t gfn)
138 {
139 int index;
140
141 if (!slot)
142 return false;
143
144 if (!kvm_page_track_write_tracking_enabled(kvm))
145 return false;
146
147 index = gfn_to_index(gfn, slot->base_gfn, PG_LEVEL_4K);
148 return !!READ_ONCE(slot->arch.gfn_write_track[index]);
149 }
150
151 #ifdef CONFIG_KVM_EXTERNAL_WRITE_TRACKING
152 void kvm_page_track_cleanup(struct kvm *kvm)
153 {
154 struct kvm_page_track_notifier_head *head;
155
156 head = &kvm->arch.track_notifier_head;
157 cleanup_srcu_struct(&head->track_srcu);
158 }
159
160 int kvm_page_track_init(struct kvm *kvm)
161 {
162 struct kvm_page_track_notifier_head *head;
163
164 head = &kvm->arch.track_notifier_head;
165 INIT_HLIST_HEAD(&head->track_notifier_list);
166 return init_srcu_struct(&head->track_srcu);
167 }
168
169 static int kvm_enable_external_write_tracking(struct kvm *kvm)
170 {
171 struct kvm_memslots *slots;
172 struct kvm_memory_slot *slot;
173 int r = 0, i, bkt;
174
175 mutex_lock(&kvm->slots_arch_lock);
176
177 /*
178 * Check for *any* write tracking user (not just external users) under
179 * lock. This avoids unnecessary work, e.g. if KVM itself is using
180 * write tracking, or if two external users raced when registering.
181 */
182 if (kvm_page_track_write_tracking_enabled(kvm))
183 goto out_success;
184
185 for (i = 0; i < kvm_arch_nr_memslot_as_ids(kvm); i++) {
186 slots = __kvm_memslots(kvm, i);
187 kvm_for_each_memslot(slot, bkt, slots) {
188 /*
189 * Intentionally do NOT free allocations on failure to
190 * avoid having to track which allocations were made
191 * now versus when the memslot was created. The
192 * metadata is guaranteed to be freed when the slot is
193 * freed, and will be kept/used if userspace retries
194 * the failed ioctl() instead of killing the VM.
195 */
196 r = kvm_page_track_write_tracking_alloc(slot);
197 if (r)
198 goto out_unlock;
199 }
200 }
201
202 out_success:
203 /*
204 * Ensure that external_write_tracking_enabled becomes true strictly
205 * after all the related pointers are set.
206 */
207 smp_store_release(&kvm->arch.external_write_tracking_enabled, true);
208 out_unlock:
209 mutex_unlock(&kvm->slots_arch_lock);
210 return r;
211 }
212
213 /*
214 * register the notifier so that event interception for the tracked guest
215 * pages can be received.
216 */
217 int kvm_page_track_register_notifier(struct kvm *kvm,
218 struct kvm_page_track_notifier_node *n)
219 {
220 struct kvm_page_track_notifier_head *head;
221 int r;
222
223 if (!kvm || kvm->mm != current->mm)
224 return -ESRCH;
225
226 if (!kvm_external_write_tracking_enabled(kvm)) {
227 r = kvm_enable_external_write_tracking(kvm);
228 if (r)
229 return r;
230 }
231
232 kvm_get_kvm(kvm);
233
234 head = &kvm->arch.track_notifier_head;
235
236 write_lock(&kvm->mmu_lock);
237 hlist_add_head_rcu(&n->node, &head->track_notifier_list);
238 write_unlock(&kvm->mmu_lock);
239 return 0;
240 }
241 EXPORT_SYMBOL_GPL(kvm_page_track_register_notifier);
242
243 /*
244 * stop receiving the event interception. It is the opposed operation of
245 * kvm_page_track_register_notifier().
246 */
247 void kvm_page_track_unregister_notifier(struct kvm *kvm,
248 struct kvm_page_track_notifier_node *n)
249 {
250 struct kvm_page_track_notifier_head *head;
251
252 head = &kvm->arch.track_notifier_head;
253
254 write_lock(&kvm->mmu_lock);
255 hlist_del_rcu(&n->node);
256 write_unlock(&kvm->mmu_lock);
257 synchronize_srcu(&head->track_srcu);
258
259 kvm_put_kvm(kvm);
260 }
261 EXPORT_SYMBOL_GPL(kvm_page_track_unregister_notifier);
262
263 /*
264 * Notify the node that write access is intercepted and write emulation is
265 * finished at this time.
266 *
267 * The node should figure out if the written page is the one that node is
268 * interested in by itself.
269 */
270 void __kvm_page_track_write(struct kvm *kvm, gpa_t gpa, const u8 *new, int bytes)
271 {
272 struct kvm_page_track_notifier_head *head;
273 struct kvm_page_track_notifier_node *n;
274 int idx;
275
276 head = &kvm->arch.track_notifier_head;
277
278 if (hlist_empty(&head->track_notifier_list))
279 return;
280
281 idx = srcu_read_lock(&head->track_srcu);
282 hlist_for_each_entry_srcu(n, &head->track_notifier_list, node,
283 srcu_read_lock_held(&head->track_srcu))
284 if (n->track_write)
285 n->track_write(gpa, new, bytes, n);
286 srcu_read_unlock(&head->track_srcu, idx);
287 }
288
289 /*
290 * Notify external page track nodes that a memory region is being removed from
291 * the VM, e.g. so that users can free any associated metadata.
292 */
293 void kvm_page_track_delete_slot(struct kvm *kvm, struct kvm_memory_slot *slot)
294 {
295 struct kvm_page_track_notifier_head *head;
296 struct kvm_page_track_notifier_node *n;
297 int idx;
298
299 head = &kvm->arch.track_notifier_head;
300
301 if (hlist_empty(&head->track_notifier_list))
302 return;
303
304 idx = srcu_read_lock(&head->track_srcu);
305 hlist_for_each_entry_srcu(n, &head->track_notifier_list, node,
306 srcu_read_lock_held(&head->track_srcu))
307 if (n->track_remove_region)
308 n->track_remove_region(slot->base_gfn, slot->npages, n);
309 srcu_read_unlock(&head->track_srcu, idx);
310 }
311
312 /*
313 * add guest page to the tracking pool so that corresponding access on that
314 * page will be intercepted.
315 *
316 * @kvm: the guest instance we are interested in.
317 * @gfn: the guest page.
318 */
319 int kvm_write_track_add_gfn(struct kvm *kvm, gfn_t gfn)
320 {
321 struct kvm_memory_slot *slot;
322 int idx;
323
324 idx = srcu_read_lock(&kvm->srcu);
325
326 slot = gfn_to_memslot(kvm, gfn);
327 if (!slot) {
328 srcu_read_unlock(&kvm->srcu, idx);
329 return -EINVAL;
330 }
331
332 write_lock(&kvm->mmu_lock);
333 __kvm_write_track_add_gfn(kvm, slot, gfn);
334 write_unlock(&kvm->mmu_lock);
335
336 srcu_read_unlock(&kvm->srcu, idx);
337
338 return 0;
339 }
340 EXPORT_SYMBOL_GPL(kvm_write_track_add_gfn);
341
342 /*
343 * remove the guest page from the tracking pool which stops the interception
344 * of corresponding access on that page.
345 *
346 * @kvm: the guest instance we are interested in.
347 * @gfn: the guest page.
348 */
349 int kvm_write_track_remove_gfn(struct kvm *kvm, gfn_t gfn)
350 {
351 struct kvm_memory_slot *slot;
352 int idx;
353
354 idx = srcu_read_lock(&kvm->srcu);
355
356 slot = gfn_to_memslot(kvm, gfn);
357 if (!slot) {
358 srcu_read_unlock(&kvm->srcu, idx);
359 return -EINVAL;
360 }
361
362 write_lock(&kvm->mmu_lock);
363 __kvm_write_track_remove_gfn(kvm, slot, gfn);
364 write_unlock(&kvm->mmu_lock);
365
366 srcu_read_unlock(&kvm->srcu, idx);
367
368 return 0;
369 }
370 EXPORT_SYMBOL_GPL(kvm_write_track_remove_gfn);
371 #endif
372
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