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1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Kernel-based Virtual Machine driver for Linux
4 *
5 * This module enables kernel and guest-mode vCPU access to guest physical
6 * memory with suitable invalidation mechanisms.
7 *
8 * Copyright © 2021 Amazon.com, Inc. or its affiliates.
9 *
10 * Authors:
11 * David Woodhouse <dwmw2@infradead.org>
12 */
13
14#include <linux/kvm_host.h>
15#include <linux/kvm.h>
16#include <linux/highmem.h>
17#include <linux/module.h>
18#include <linux/errno.h>
19
20#include "kvm_mm.h"
21
22/*
23 * MMU notifier 'invalidate_range_start' hook.
24 */
25void gfn_to_pfn_cache_invalidate_start(struct kvm *kvm, unsigned long start,
26 unsigned long end, bool may_block)
27{
28 DECLARE_BITMAP(vcpu_bitmap, KVM_MAX_VCPUS);
29 struct gfn_to_pfn_cache *gpc;
30 bool evict_vcpus = false;
31
32 spin_lock(&kvm->gpc_lock);
33 list_for_each_entry(gpc, &kvm->gpc_list, list) {
34 write_lock_irq(&gpc->lock);
35
36 /* Only a single page so no need to care about length */
37 if (gpc->valid && !is_error_noslot_pfn(gpc->pfn) &&
38 gpc->uhva >= start && gpc->uhva < end) {
39 gpc->valid = false;
40
41 /*
42 * If a guest vCPU could be using the physical address,
43 * it needs to be forced out of guest mode.
44 */
45 if (gpc->usage & KVM_GUEST_USES_PFN) {
46 if (!evict_vcpus) {
47 evict_vcpus = true;
48 bitmap_zero(vcpu_bitmap, KVM_MAX_VCPUS);
49 }
50 __set_bit(gpc->vcpu->vcpu_idx, vcpu_bitmap);
51 }
52 }
53 write_unlock_irq(&gpc->lock);
54 }
55 spin_unlock(&kvm->gpc_lock);
56
57 if (evict_vcpus) {
58 /*
59 * KVM needs to ensure the vCPU is fully out of guest context
60 * before allowing the invalidation to continue.
61 */
62 unsigned int req = KVM_REQ_OUTSIDE_GUEST_MODE;
63 bool called;
64
65 /*
66 * If the OOM reaper is active, then all vCPUs should have
67 * been stopped already, so perform the request without
68 * KVM_REQUEST_WAIT and be sad if any needed to be IPI'd.
69 */
70 if (!may_block)
71 req &= ~KVM_REQUEST_WAIT;
72
73 called = kvm_make_vcpus_request_mask(kvm, req, vcpu_bitmap);
74
75 WARN_ON_ONCE(called && !may_block);
76 }
77}
78
79bool kvm_gpc_check(struct gfn_to_pfn_cache *gpc, unsigned long len)
80{
81 struct kvm_memslots *slots = kvm_memslots(gpc->kvm);
82
83 if (!gpc->active)
84 return false;
85
86 if ((gpc->gpa & ~PAGE_MASK) + len > PAGE_SIZE)
87 return false;
88
89 if (gpc->generation != slots->generation || kvm_is_error_hva(gpc->uhva))
90 return false;
91
92 if (!gpc->valid)
93 return false;
94
95 return true;
96}
97EXPORT_SYMBOL_GPL(kvm_gpc_check);
98
99static void gpc_unmap_khva(kvm_pfn_t pfn, void *khva)
100{
101 /* Unmap the old pfn/page if it was mapped before. */
102 if (!is_error_noslot_pfn(pfn) && khva) {
103 if (pfn_valid(pfn))
104 kunmap(pfn_to_page(pfn));
105#ifdef CONFIG_HAS_IOMEM
106 else
107 memunmap(khva);
108#endif
109 }
110}
111
112static inline bool mmu_notifier_retry_cache(struct kvm *kvm, unsigned long mmu_seq)
113{
114 /*
115 * mn_active_invalidate_count acts for all intents and purposes
116 * like mmu_invalidate_in_progress here; but the latter cannot
117 * be used here because the invalidation of caches in the
118 * mmu_notifier event occurs _before_ mmu_invalidate_in_progress
119 * is elevated.
120 *
121 * Note, it does not matter that mn_active_invalidate_count
122 * is not protected by gpc->lock. It is guaranteed to
123 * be elevated before the mmu_notifier acquires gpc->lock, and
124 * isn't dropped until after mmu_invalidate_seq is updated.
125 */
126 if (kvm->mn_active_invalidate_count)
127 return true;
128
129 /*
130 * Ensure mn_active_invalidate_count is read before
131 * mmu_invalidate_seq. This pairs with the smp_wmb() in
132 * mmu_notifier_invalidate_range_end() to guarantee either the
133 * old (non-zero) value of mn_active_invalidate_count or the
134 * new (incremented) value of mmu_invalidate_seq is observed.
135 */
136 smp_rmb();
137 return kvm->mmu_invalidate_seq != mmu_seq;
138}
139
140static kvm_pfn_t hva_to_pfn_retry(struct gfn_to_pfn_cache *gpc)
141{
142 /* Note, the new page offset may be different than the old! */
143 void *old_khva = gpc->khva - offset_in_page(gpc->khva);
144 kvm_pfn_t new_pfn = KVM_PFN_ERR_FAULT;
145 void *new_khva = NULL;
146 unsigned long mmu_seq;
147
148 lockdep_assert_held(&gpc->refresh_lock);
149
150 lockdep_assert_held_write(&gpc->lock);
151
152 /*
153 * Invalidate the cache prior to dropping gpc->lock, the gpa=>uhva
154 * assets have already been updated and so a concurrent check() from a
155 * different task may not fail the gpa/uhva/generation checks.
156 */
157 gpc->valid = false;
158
159 do {
160 mmu_seq = gpc->kvm->mmu_invalidate_seq;
161 smp_rmb();
162
163 write_unlock_irq(&gpc->lock);
164
165 /*
166 * If the previous iteration "failed" due to an mmu_notifier
167 * event, release the pfn and unmap the kernel virtual address
168 * from the previous attempt. Unmapping might sleep, so this
169 * needs to be done after dropping the lock. Opportunistically
170 * check for resched while the lock isn't held.
171 */
172 if (new_pfn != KVM_PFN_ERR_FAULT) {
173 /*
174 * Keep the mapping if the previous iteration reused
175 * the existing mapping and didn't create a new one.
176 */
177 if (new_khva != old_khva)
178 gpc_unmap_khva(new_pfn, new_khva);
179
180 kvm_release_pfn_clean(new_pfn);
181
182 cond_resched();
183 }
184
185 /* We always request a writeable mapping */
186 new_pfn = hva_to_pfn(gpc->uhva, false, false, NULL, true, NULL);
187 if (is_error_noslot_pfn(new_pfn))
188 goto out_error;
189
190 /*
191 * Obtain a new kernel mapping if KVM itself will access the
192 * pfn. Note, kmap() and memremap() can both sleep, so this
193 * too must be done outside of gpc->lock!
194 */
195 if (gpc->usage & KVM_HOST_USES_PFN) {
196 if (new_pfn == gpc->pfn) {
197 new_khva = old_khva;
198 } else if (pfn_valid(new_pfn)) {
199 new_khva = kmap(pfn_to_page(new_pfn));
200#ifdef CONFIG_HAS_IOMEM
201 } else {
202 new_khva = memremap(pfn_to_hpa(new_pfn), PAGE_SIZE, MEMREMAP_WB);
203#endif
204 }
205 if (!new_khva) {
206 kvm_release_pfn_clean(new_pfn);
207 goto out_error;
208 }
209 }
210
211 write_lock_irq(&gpc->lock);
212
213 /*
214 * Other tasks must wait for _this_ refresh to complete before
215 * attempting to refresh.
216 */
217 WARN_ON_ONCE(gpc->valid);
218 } while (mmu_notifier_retry_cache(gpc->kvm, mmu_seq));
219
220 gpc->valid = true;
221 gpc->pfn = new_pfn;
222 gpc->khva = new_khva + (gpc->gpa & ~PAGE_MASK);
223
224 /*
225 * Put the reference to the _new_ pfn. The pfn is now tracked by the
226 * cache and can be safely migrated, swapped, etc... as the cache will
227 * invalidate any mappings in response to relevant mmu_notifier events.
228 */
229 kvm_release_pfn_clean(new_pfn);
230
231 return 0;
232
233out_error:
234 write_lock_irq(&gpc->lock);
235
236 return -EFAULT;
237}
238
239static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa,
240 unsigned long len)
241{
242 struct kvm_memslots *slots = kvm_memslots(gpc->kvm);
243 unsigned long page_offset = gpa & ~PAGE_MASK;
244 bool unmap_old = false;
245 unsigned long old_uhva;
246 kvm_pfn_t old_pfn;
247 void *old_khva;
248 int ret;
249
250 /*
251 * If must fit within a single page. The 'len' argument is
252 * only to enforce that.
253 */
254 if (page_offset + len > PAGE_SIZE)
255 return -EINVAL;
256
257 /*
258 * If another task is refreshing the cache, wait for it to complete.
259 * There is no guarantee that concurrent refreshes will see the same
260 * gpa, memslots generation, etc..., so they must be fully serialized.
261 */
262 mutex_lock(&gpc->refresh_lock);
263
264 write_lock_irq(&gpc->lock);
265
266 if (!gpc->active) {
267 ret = -EINVAL;
268 goto out_unlock;
269 }
270
271 old_pfn = gpc->pfn;
272 old_khva = gpc->khva - offset_in_page(gpc->khva);
273 old_uhva = gpc->uhva;
274
275 /* If the userspace HVA is invalid, refresh that first */
276 if (gpc->gpa != gpa || gpc->generation != slots->generation ||
277 kvm_is_error_hva(gpc->uhva)) {
278 gfn_t gfn = gpa_to_gfn(gpa);
279
280 gpc->gpa = gpa;
281 gpc->generation = slots->generation;
282 gpc->memslot = __gfn_to_memslot(slots, gfn);
283 gpc->uhva = gfn_to_hva_memslot(gpc->memslot, gfn);
284
285 if (kvm_is_error_hva(gpc->uhva)) {
286 ret = -EFAULT;
287 goto out;
288 }
289 }
290
291 /*
292 * If the userspace HVA changed or the PFN was already invalid,
293 * drop the lock and do the HVA to PFN lookup again.
294 */
295 if (!gpc->valid || old_uhva != gpc->uhva) {
296 ret = hva_to_pfn_retry(gpc);
297 } else {
298 /*
299 * If the HVA→PFN mapping was already valid, don't unmap it.
300 * But do update gpc->khva because the offset within the page
301 * may have changed.
302 */
303 gpc->khva = old_khva + page_offset;
304 ret = 0;
305 goto out_unlock;
306 }
307
308 out:
309 /*
310 * Invalidate the cache and purge the pfn/khva if the refresh failed.
311 * Some/all of the uhva, gpa, and memslot generation info may still be
312 * valid, leave it as is.
313 */
314 if (ret) {
315 gpc->valid = false;
316 gpc->pfn = KVM_PFN_ERR_FAULT;
317 gpc->khva = NULL;
318 }
319
320 /* Detect a pfn change before dropping the lock! */
321 unmap_old = (old_pfn != gpc->pfn);
322
323out_unlock:
324 write_unlock_irq(&gpc->lock);
325
326 mutex_unlock(&gpc->refresh_lock);
327
328 if (unmap_old)
329 gpc_unmap_khva(old_pfn, old_khva);
330
331 return ret;
332}
333
334int kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, unsigned long len)
335{
336 return __kvm_gpc_refresh(gpc, gpc->gpa, len);
337}
338EXPORT_SYMBOL_GPL(kvm_gpc_refresh);
339
340void kvm_gpc_init(struct gfn_to_pfn_cache *gpc, struct kvm *kvm,
341 struct kvm_vcpu *vcpu, enum pfn_cache_usage usage)
342{
343 WARN_ON_ONCE(!usage || (usage & KVM_GUEST_AND_HOST_USE_PFN) != usage);
344 WARN_ON_ONCE((usage & KVM_GUEST_USES_PFN) && !vcpu);
345
346 rwlock_init(&gpc->lock);
347 mutex_init(&gpc->refresh_lock);
348
349 gpc->kvm = kvm;
350 gpc->vcpu = vcpu;
351 gpc->usage = usage;
352 gpc->pfn = KVM_PFN_ERR_FAULT;
353 gpc->uhva = KVM_HVA_ERR_BAD;
354}
355EXPORT_SYMBOL_GPL(kvm_gpc_init);
356
357int kvm_gpc_activate(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long len)
358{
359 struct kvm *kvm = gpc->kvm;
360
361 if (!gpc->active) {
362 if (KVM_BUG_ON(gpc->valid, kvm))
363 return -EIO;
364
365 spin_lock(&kvm->gpc_lock);
366 list_add(&gpc->list, &kvm->gpc_list);
367 spin_unlock(&kvm->gpc_lock);
368
369 /*
370 * Activate the cache after adding it to the list, a concurrent
371 * refresh must not establish a mapping until the cache is
372 * reachable by mmu_notifier events.
373 */
374 write_lock_irq(&gpc->lock);
375 gpc->active = true;
376 write_unlock_irq(&gpc->lock);
377 }
378 return __kvm_gpc_refresh(gpc, gpa, len);
379}
380EXPORT_SYMBOL_GPL(kvm_gpc_activate);
381
382void kvm_gpc_deactivate(struct gfn_to_pfn_cache *gpc)
383{
384 struct kvm *kvm = gpc->kvm;
385 kvm_pfn_t old_pfn;
386 void *old_khva;
387
388 if (gpc->active) {
389 /*
390 * Deactivate the cache before removing it from the list, KVM
391 * must stall mmu_notifier events until all users go away, i.e.
392 * until gpc->lock is dropped and refresh is guaranteed to fail.
393 */
394 write_lock_irq(&gpc->lock);
395 gpc->active = false;
396 gpc->valid = false;
397
398 /*
399 * Leave the GPA => uHVA cache intact, it's protected by the
400 * memslot generation. The PFN lookup needs to be redone every
401 * time as mmu_notifier protection is lost when the cache is
402 * removed from the VM's gpc_list.
403 */
404 old_khva = gpc->khva - offset_in_page(gpc->khva);
405 gpc->khva = NULL;
406
407 old_pfn = gpc->pfn;
408 gpc->pfn = KVM_PFN_ERR_FAULT;
409 write_unlock_irq(&gpc->lock);
410
411 spin_lock(&kvm->gpc_lock);
412 list_del(&gpc->list);
413 spin_unlock(&kvm->gpc_lock);
414
415 gpc_unmap_khva(old_pfn, old_khva);
416 }
417}
418EXPORT_SYMBOL_GPL(kvm_gpc_deactivate);