1 /*
2  * Copyright 2013 Red Hat Inc.
3  *
4  * This program is free software; you can redistribute it and/or modify
5  * it under the terms of the GNU General Public License as published by
6  * the Free Software Foundation; either version 2 of the License, or
7  * (at your option) any later version.
8  *
9  * This program is distributed in the hope that it will be useful,
10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
12  * GNU General Public License for more details.
13  *
14  * Authors: Jérôme Glisse <jglisse@redhat.com>
15  */
16 /*
17  * Heterogeneous Memory Management (HMM)
18  *
19  * See Documentation/vm/hmm.rst for reasons and overview of what HMM is and it
20  * is for. Here we focus on the HMM API description, with some explanation of
21  * the underlying implementation.
22  *
23  * Short description: HMM provides a set of helpers to share a virtual address
24  * space between CPU and a device, so that the device can access any valid
25  * address of the process (while still obeying memory protection). HMM also
26  * provides helpers to migrate process memory to device memory, and back. Each
27  * set of functionality (address space mirroring, and migration to and from
28  * device memory) can be used independently of the other.
29  *
30  *
31  * HMM address space mirroring API:
32  *
33  * Use HMM address space mirroring if you want to mirror range of the CPU page
34  * table of a process into a device page table. Here, "mirror" means "keep
35  * synchronized". Prerequisites: the device must provide the ability to write-
36  * protect its page tables (at PAGE_SIZE granularity), and must be able to
37  * recover from the resulting potential page faults.
38  *
39  * HMM guarantees that at any point in time, a given virtual address points to
40  * either the same memory in both CPU and device page tables (that is: CPU and
41  * device page tables each point to the same pages), or that one page table (CPU
42  * or device) points to no entry, while the other still points to the old page
43  * for the address. The latter case happens when the CPU page table update
44  * happens first, and then the update is mirrored over to the device page table.
45  * This does not cause any issue, because the CPU page table cannot start
46  * pointing to a new page until the device page table is invalidated.
47  *
48  * HMM uses mmu_notifiers to monitor the CPU page tables, and forwards any
49  * updates to each device driver that has registered a mirror. It also provides
50  * some API calls to help with taking a snapshot of the CPU page table, and to
51  * synchronize with any updates that might happen concurrently.
52  *
53  *
54  * HMM migration to and from device memory:
55  *
56  * HMM provides a set of helpers to hotplug device memory as ZONE_DEVICE, with
57  * a new MEMORY_DEVICE_PRIVATE type. This provides a struct page for each page
58  * of the device memory, and allows the device driver to manage its memory
59  * using those struct pages. Having struct pages for device memory makes
60  * migration easier. Because that memory is not addressable by the CPU it must
61  * never be pinned to the device; in other words, any CPU page fault can always
62  * cause the device memory to be migrated (copied/moved) back to regular memory.
63  *
64  * A new migrate helper (migrate_vma()) has been added (see mm/migrate.c) that
65  * allows use of a device DMA engine to perform the copy operation between
66  * regular system memory and device memory.
67  */
68 #ifndef LINUX_HMM_H
69 #define LINUX_HMM_H
70 
71 #include <linux/kconfig.h>
72 
73 #if IS_ENABLED(CONFIG_HMM)
74 
75 #include <linux/device.h>
76 #include <linux/migrate.h>
77 #include <linux/memremap.h>
78 #include <linux/completion.h>
79 
80 struct hmm;
81 
82 /*
83  * hmm_pfn_flag_e - HMM flag enums
84  *
85  * Flags:
86  * HMM_PFN_VALID: pfn is valid. It has, at least, read permission.
87  * HMM_PFN_WRITE: CPU page table has write permission set
88  * HMM_PFN_DEVICE_PRIVATE: private device memory (ZONE_DEVICE)
89  *
90  * The driver provide a flags array, if driver valid bit for an entry is bit
91  * 3 ie (entry & (1 << 3)) is true if entry is valid then driver must provide
92  * an array in hmm_range.flags with hmm_range.flags[HMM_PFN_VALID] == 1 << 3.
93  * Same logic apply to all flags. This is same idea as vm_page_prot in vma
94  * except that this is per device driver rather than per architecture.
95  */
96 enum hmm_pfn_flag_e {
97 	HMM_PFN_VALID = 0,
98 	HMM_PFN_WRITE,
99 	HMM_PFN_DEVICE_PRIVATE,
100 	HMM_PFN_FLAG_MAX
101 };
102 
103 /*
104  * hmm_pfn_value_e - HMM pfn special value
105  *
106  * Flags:
107  * HMM_PFN_ERROR: corresponding CPU page table entry points to poisoned memory
108  * HMM_PFN_NONE: corresponding CPU page table entry is pte_none()
109  * HMM_PFN_SPECIAL: corresponding CPU page table entry is special; i.e., the
110  *      result of vm_insert_pfn() or vm_insert_page(). Therefore, it should not
111  *      be mirrored by a device, because the entry will never have HMM_PFN_VALID
112  *      set and the pfn value is undefined.
113  *
114  * Driver provide entry value for none entry, error entry and special entry,
115  * driver can alias (ie use same value for error and special for instance). It
116  * should not alias none and error or special.
117  *
118  * HMM pfn value returned by hmm_vma_get_pfns() or hmm_vma_fault() will be:
119  * hmm_range.values[HMM_PFN_ERROR] if CPU page table entry is poisonous,
120  * hmm_range.values[HMM_PFN_NONE] if there is no CPU page table
121  * hmm_range.values[HMM_PFN_SPECIAL] if CPU page table entry is a special one
122  */
123 enum hmm_pfn_value_e {
124 	HMM_PFN_ERROR,
125 	HMM_PFN_NONE,
126 	HMM_PFN_SPECIAL,
127 	HMM_PFN_VALUE_MAX
128 };
129 
130 /*
131  * struct hmm_range - track invalidation lock on virtual address range
132  *
133  * @vma: the vm area struct for the range
134  * @list: all range lock are on a list
135  * @start: range virtual start address (inclusive)
136  * @end: range virtual end address (exclusive)
137  * @pfns: array of pfns (big enough for the range)
138  * @flags: pfn flags to match device driver page table
139  * @values: pfn value for some special case (none, special, error, ...)
140  * @pfn_shifts: pfn shift value (should be <= PAGE_SHIFT)
141  * @valid: pfns array did not change since it has been fill by an HMM function
142  */
143 struct hmm_range {
144 	struct vm_area_struct	*vma;
145 	struct list_head	list;
146 	unsigned long		start;
147 	unsigned long		end;
148 	uint64_t		*pfns;
149 	const uint64_t		*flags;
150 	const uint64_t		*values;
151 	uint8_t			pfn_shift;
152 	bool			valid;
153 };
154 
155 /*
156  * hmm_pfn_to_page() - return struct page pointed to by a valid HMM pfn
157  * @range: range use to decode HMM pfn value
158  * @pfn: HMM pfn value to get corresponding struct page from
159  * Returns: struct page pointer if pfn is a valid HMM pfn, NULL otherwise
160  *
161  * If the HMM pfn is valid (ie valid flag set) then return the struct page
162  * matching the pfn value stored in the HMM pfn. Otherwise return NULL.
163  */
hmm_pfn_to_page(const struct hmm_range * range,uint64_t pfn)164 static inline struct page *hmm_pfn_to_page(const struct hmm_range *range,
165 					   uint64_t pfn)
166 {
167 	if (pfn == range->values[HMM_PFN_NONE])
168 		return NULL;
169 	if (pfn == range->values[HMM_PFN_ERROR])
170 		return NULL;
171 	if (pfn == range->values[HMM_PFN_SPECIAL])
172 		return NULL;
173 	if (!(pfn & range->flags[HMM_PFN_VALID]))
174 		return NULL;
175 	return pfn_to_page(pfn >> range->pfn_shift);
176 }
177 
178 /*
179  * hmm_pfn_to_pfn() - return pfn value store in a HMM pfn
180  * @range: range use to decode HMM pfn value
181  * @pfn: HMM pfn value to extract pfn from
182  * Returns: pfn value if HMM pfn is valid, -1UL otherwise
183  */
hmm_pfn_to_pfn(const struct hmm_range * range,uint64_t pfn)184 static inline unsigned long hmm_pfn_to_pfn(const struct hmm_range *range,
185 					   uint64_t pfn)
186 {
187 	if (pfn == range->values[HMM_PFN_NONE])
188 		return -1UL;
189 	if (pfn == range->values[HMM_PFN_ERROR])
190 		return -1UL;
191 	if (pfn == range->values[HMM_PFN_SPECIAL])
192 		return -1UL;
193 	if (!(pfn & range->flags[HMM_PFN_VALID]))
194 		return -1UL;
195 	return (pfn >> range->pfn_shift);
196 }
197 
198 /*
199  * hmm_pfn_from_page() - create a valid HMM pfn value from struct page
200  * @range: range use to encode HMM pfn value
201  * @page: struct page pointer for which to create the HMM pfn
202  * Returns: valid HMM pfn for the page
203  */
hmm_pfn_from_page(const struct hmm_range * range,struct page * page)204 static inline uint64_t hmm_pfn_from_page(const struct hmm_range *range,
205 					 struct page *page)
206 {
207 	return (page_to_pfn(page) << range->pfn_shift) |
208 		range->flags[HMM_PFN_VALID];
209 }
210 
211 /*
212  * hmm_pfn_from_pfn() - create a valid HMM pfn value from pfn
213  * @range: range use to encode HMM pfn value
214  * @pfn: pfn value for which to create the HMM pfn
215  * Returns: valid HMM pfn for the pfn
216  */
hmm_pfn_from_pfn(const struct hmm_range * range,unsigned long pfn)217 static inline uint64_t hmm_pfn_from_pfn(const struct hmm_range *range,
218 					unsigned long pfn)
219 {
220 	return (pfn << range->pfn_shift) |
221 		range->flags[HMM_PFN_VALID];
222 }
223 
224 
225 #if IS_ENABLED(CONFIG_HMM_MIRROR)
226 /*
227  * Mirroring: how to synchronize device page table with CPU page table.
228  *
229  * A device driver that is participating in HMM mirroring must always
230  * synchronize with CPU page table updates. For this, device drivers can either
231  * directly use mmu_notifier APIs or they can use the hmm_mirror API. Device
232  * drivers can decide to register one mirror per device per process, or just
233  * one mirror per process for a group of devices. The pattern is:
234  *
235  *      int device_bind_address_space(..., struct mm_struct *mm, ...)
236  *      {
237  *          struct device_address_space *das;
238  *
239  *          // Device driver specific initialization, and allocation of das
240  *          // which contains an hmm_mirror struct as one of its fields.
241  *          ...
242  *
243  *          ret = hmm_mirror_register(&das->mirror, mm, &device_mirror_ops);
244  *          if (ret) {
245  *              // Cleanup on error
246  *              return ret;
247  *          }
248  *
249  *          // Other device driver specific initialization
250  *          ...
251  *      }
252  *
253  * Once an hmm_mirror is registered for an address space, the device driver
254  * will get callbacks through sync_cpu_device_pagetables() operation (see
255  * hmm_mirror_ops struct).
256  *
257  * Device driver must not free the struct containing the hmm_mirror struct
258  * before calling hmm_mirror_unregister(). The expected usage is to do that when
259  * the device driver is unbinding from an address space.
260  *
261  *
262  *      void device_unbind_address_space(struct device_address_space *das)
263  *      {
264  *          // Device driver specific cleanup
265  *          ...
266  *
267  *          hmm_mirror_unregister(&das->mirror);
268  *
269  *          // Other device driver specific cleanup, and now das can be freed
270  *          ...
271  *      }
272  */
273 
274 struct hmm_mirror;
275 
276 /*
277  * enum hmm_update_type - type of update
278  * @HMM_UPDATE_INVALIDATE: invalidate range (no indication as to why)
279  */
280 enum hmm_update_type {
281 	HMM_UPDATE_INVALIDATE,
282 };
283 
284 /*
285  * struct hmm_mirror_ops - HMM mirror device operations callback
286  *
287  * @update: callback to update range on a device
288  */
289 struct hmm_mirror_ops {
290 	/* release() - release hmm_mirror
291 	 *
292 	 * @mirror: pointer to struct hmm_mirror
293 	 *
294 	 * This is called when the mm_struct is being released.
295 	 * The callback should make sure no references to the mirror occur
296 	 * after the callback returns.
297 	 */
298 	void (*release)(struct hmm_mirror *mirror);
299 
300 	/* sync_cpu_device_pagetables() - synchronize page tables
301 	 *
302 	 * @mirror: pointer to struct hmm_mirror
303 	 * @update_type: type of update that occurred to the CPU page table
304 	 * @start: virtual start address of the range to update
305 	 * @end: virtual end address of the range to update
306 	 *
307 	 * This callback ultimately originates from mmu_notifiers when the CPU
308 	 * page table is updated. The device driver must update its page table
309 	 * in response to this callback. The update argument tells what action
310 	 * to perform.
311 	 *
312 	 * The device driver must not return from this callback until the device
313 	 * page tables are completely updated (TLBs flushed, etc); this is a
314 	 * synchronous call.
315 	 */
316 	void (*sync_cpu_device_pagetables)(struct hmm_mirror *mirror,
317 					   enum hmm_update_type update_type,
318 					   unsigned long start,
319 					   unsigned long end);
320 };
321 
322 /*
323  * struct hmm_mirror - mirror struct for a device driver
324  *
325  * @hmm: pointer to struct hmm (which is unique per mm_struct)
326  * @ops: device driver callback for HMM mirror operations
327  * @list: for list of mirrors of a given mm
328  *
329  * Each address space (mm_struct) being mirrored by a device must register one
330  * instance of an hmm_mirror struct with HMM. HMM will track the list of all
331  * mirrors for each mm_struct.
332  */
333 struct hmm_mirror {
334 	struct hmm			*hmm;
335 	const struct hmm_mirror_ops	*ops;
336 	struct list_head		list;
337 };
338 
339 int hmm_mirror_register(struct hmm_mirror *mirror, struct mm_struct *mm);
340 void hmm_mirror_unregister(struct hmm_mirror *mirror);
341 
342 
343 /*
344  * To snapshot the CPU page table, call hmm_vma_get_pfns(), then take a device
345  * driver lock that serializes device page table updates, then call
346  * hmm_vma_range_done(), to check if the snapshot is still valid. The same
347  * device driver page table update lock must also be used in the
348  * hmm_mirror_ops.sync_cpu_device_pagetables() callback, so that CPU page
349  * table invalidation serializes on it.
350  *
351  * YOU MUST CALL hmm_vma_range_done() ONCE AND ONLY ONCE EACH TIME YOU CALL
352  * hmm_vma_get_pfns() WITHOUT ERROR !
353  *
354  * IF YOU DO NOT FOLLOW THE ABOVE RULE THE SNAPSHOT CONTENT MIGHT BE INVALID !
355  */
356 int hmm_vma_get_pfns(struct hmm_range *range);
357 bool hmm_vma_range_done(struct hmm_range *range);
358 
359 
360 /*
361  * Fault memory on behalf of device driver. Unlike handle_mm_fault(), this will
362  * not migrate any device memory back to system memory. The HMM pfn array will
363  * be updated with the fault result and current snapshot of the CPU page table
364  * for the range.
365  *
366  * The mmap_sem must be taken in read mode before entering and it might be
367  * dropped by the function if the block argument is false. In that case, the
368  * function returns -EAGAIN.
369  *
370  * Return value does not reflect if the fault was successful for every single
371  * address or not. Therefore, the caller must to inspect the HMM pfn array to
372  * determine fault status for each address.
373  *
374  * Trying to fault inside an invalid vma will result in -EINVAL.
375  *
376  * See the function description in mm/hmm.c for further documentation.
377  */
378 int hmm_vma_fault(struct hmm_range *range, bool block);
379 
380 /* Below are for HMM internal use only! Not to be used by device driver! */
381 void hmm_mm_destroy(struct mm_struct *mm);
382 
hmm_mm_init(struct mm_struct * mm)383 static inline void hmm_mm_init(struct mm_struct *mm)
384 {
385 	mm->hmm = NULL;
386 }
387 #else /* IS_ENABLED(CONFIG_HMM_MIRROR) */
hmm_mm_destroy(struct mm_struct * mm)388 static inline void hmm_mm_destroy(struct mm_struct *mm) {}
hmm_mm_init(struct mm_struct * mm)389 static inline void hmm_mm_init(struct mm_struct *mm) {}
390 #endif /* IS_ENABLED(CONFIG_HMM_MIRROR) */
391 
392 #if IS_ENABLED(CONFIG_DEVICE_PRIVATE) ||  IS_ENABLED(CONFIG_DEVICE_PUBLIC)
393 struct hmm_devmem;
394 
395 struct page *hmm_vma_alloc_locked_page(struct vm_area_struct *vma,
396 				       unsigned long addr);
397 
398 /*
399  * struct hmm_devmem_ops - callback for ZONE_DEVICE memory events
400  *
401  * @free: call when refcount on page reach 1 and thus is no longer use
402  * @fault: call when there is a page fault to unaddressable memory
403  *
404  * Both callback happens from page_free() and page_fault() callback of struct
405  * dev_pagemap respectively. See include/linux/memremap.h for more details on
406  * those.
407  *
408  * The hmm_devmem_ops callback are just here to provide a coherent and
409  * uniq API to device driver and device driver should not register their
410  * own page_free() or page_fault() but rely on the hmm_devmem_ops call-
411  * back.
412  */
413 struct hmm_devmem_ops {
414 	/*
415 	 * free() - free a device page
416 	 * @devmem: device memory structure (see struct hmm_devmem)
417 	 * @page: pointer to struct page being freed
418 	 *
419 	 * Call back occurs whenever a device page refcount reach 1 which
420 	 * means that no one is holding any reference on the page anymore
421 	 * (ZONE_DEVICE page have an elevated refcount of 1 as default so
422 	 * that they are not release to the general page allocator).
423 	 *
424 	 * Note that callback has exclusive ownership of the page (as no
425 	 * one is holding any reference).
426 	 */
427 	void (*free)(struct hmm_devmem *devmem, struct page *page);
428 	/*
429 	 * fault() - CPU page fault or get user page (GUP)
430 	 * @devmem: device memory structure (see struct hmm_devmem)
431 	 * @vma: virtual memory area containing the virtual address
432 	 * @addr: virtual address that faulted or for which there is a GUP
433 	 * @page: pointer to struct page backing virtual address (unreliable)
434 	 * @flags: FAULT_FLAG_* (see include/linux/mm.h)
435 	 * @pmdp: page middle directory
436 	 * Returns: VM_FAULT_MINOR/MAJOR on success or one of VM_FAULT_ERROR
437 	 *   on error
438 	 *
439 	 * The callback occurs whenever there is a CPU page fault or GUP on a
440 	 * virtual address. This means that the device driver must migrate the
441 	 * page back to regular memory (CPU accessible).
442 	 *
443 	 * The device driver is free to migrate more than one page from the
444 	 * fault() callback as an optimization. However if device decide to
445 	 * migrate more than one page it must always priotirize the faulting
446 	 * address over the others.
447 	 *
448 	 * The struct page pointer is only given as an hint to allow quick
449 	 * lookup of internal device driver data. A concurrent migration
450 	 * might have already free that page and the virtual address might
451 	 * not longer be back by it. So it should not be modified by the
452 	 * callback.
453 	 *
454 	 * Note that mmap semaphore is held in read mode at least when this
455 	 * callback occurs, hence the vma is valid upon callback entry.
456 	 */
457 	int (*fault)(struct hmm_devmem *devmem,
458 		     struct vm_area_struct *vma,
459 		     unsigned long addr,
460 		     const struct page *page,
461 		     unsigned int flags,
462 		     pmd_t *pmdp);
463 };
464 
465 /*
466  * struct hmm_devmem - track device memory
467  *
468  * @completion: completion object for device memory
469  * @pfn_first: first pfn for this resource (set by hmm_devmem_add())
470  * @pfn_last: last pfn for this resource (set by hmm_devmem_add())
471  * @resource: IO resource reserved for this chunk of memory
472  * @pagemap: device page map for that chunk
473  * @device: device to bind resource to
474  * @ops: memory operations callback
475  * @ref: per CPU refcount
476  *
477  * This an helper structure for device drivers that do not wish to implement
478  * the gory details related to hotplugging new memoy and allocating struct
479  * pages.
480  *
481  * Device drivers can directly use ZONE_DEVICE memory on their own if they
482  * wish to do so.
483  */
484 struct hmm_devmem {
485 	struct completion		completion;
486 	unsigned long			pfn_first;
487 	unsigned long			pfn_last;
488 	struct resource			*resource;
489 	struct device			*device;
490 	struct dev_pagemap		pagemap;
491 	const struct hmm_devmem_ops	*ops;
492 	struct percpu_ref		ref;
493 };
494 
495 /*
496  * To add (hotplug) device memory, HMM assumes that there is no real resource
497  * that reserves a range in the physical address space (this is intended to be
498  * use by unaddressable device memory). It will reserve a physical range big
499  * enough and allocate struct page for it.
500  *
501  * The device driver can wrap the hmm_devmem struct inside a private device
502  * driver struct.
503  */
504 struct hmm_devmem *hmm_devmem_add(const struct hmm_devmem_ops *ops,
505 				  struct device *device,
506 				  unsigned long size);
507 struct hmm_devmem *hmm_devmem_add_resource(const struct hmm_devmem_ops *ops,
508 					   struct device *device,
509 					   struct resource *res);
510 
511 /*
512  * hmm_devmem_page_set_drvdata - set per-page driver data field
513  *
514  * @page: pointer to struct page
515  * @data: driver data value to set
516  *
517  * Because page can not be on lru we have an unsigned long that driver can use
518  * to store a per page field. This just a simple helper to do that.
519  */
hmm_devmem_page_set_drvdata(struct page * page,unsigned long data)520 static inline void hmm_devmem_page_set_drvdata(struct page *page,
521 					       unsigned long data)
522 {
523 	page->hmm_data = data;
524 }
525 
526 /*
527  * hmm_devmem_page_get_drvdata - get per page driver data field
528  *
529  * @page: pointer to struct page
530  * Return: driver data value
531  */
hmm_devmem_page_get_drvdata(const struct page * page)532 static inline unsigned long hmm_devmem_page_get_drvdata(const struct page *page)
533 {
534 	return page->hmm_data;
535 }
536 
537 
538 /*
539  * struct hmm_device - fake device to hang device memory onto
540  *
541  * @device: device struct
542  * @minor: device minor number
543  */
544 struct hmm_device {
545 	struct device		device;
546 	unsigned int		minor;
547 };
548 
549 /*
550  * A device driver that wants to handle multiple devices memory through a
551  * single fake device can use hmm_device to do so. This is purely a helper and
552  * it is not strictly needed, in order to make use of any HMM functionality.
553  */
554 struct hmm_device *hmm_device_new(void *drvdata);
555 void hmm_device_put(struct hmm_device *hmm_device);
556 #endif /* CONFIG_DEVICE_PRIVATE || CONFIG_DEVICE_PUBLIC */
557 #else /* IS_ENABLED(CONFIG_HMM) */
hmm_mm_destroy(struct mm_struct * mm)558 static inline void hmm_mm_destroy(struct mm_struct *mm) {}
hmm_mm_init(struct mm_struct * mm)559 static inline void hmm_mm_init(struct mm_struct *mm) {}
560 #endif /* IS_ENABLED(CONFIG_HMM) */
561 
562 #endif /* LINUX_HMM_H */
563