summaryrefslogtreecommitdiffstats
path: root/include/linux/hmm.h
blob: ddf9f7144c430e264a713886c0af593893bd8b53 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
/* SPDX-License-Identifier: GPL-2.0-or-later */
/*
 * Copyright 2013 Red Hat Inc.
 *
 * Authors: Jérôme Glisse <jglisse@redhat.com>
 */
/*
 * Heterogeneous Memory Management (HMM)
 *
 * See Documentation/vm/hmm.rst for reasons and overview of what HMM is and it
 * is for. Here we focus on the HMM API description, with some explanation of
 * the underlying implementation.
 *
 * Short description: HMM provides a set of helpers to share a virtual address
 * space between CPU and a device, so that the device can access any valid
 * address of the process (while still obeying memory protection). HMM also
 * provides helpers to migrate process memory to device memory, and back. Each
 * set of functionality (address space mirroring, and migration to and from
 * device memory) can be used independently of the other.
 *
 *
 * HMM address space mirroring API:
 *
 * Use HMM address space mirroring if you want to mirror a range of the CPU
 * page tables of a process into a device page table. Here, "mirror" means "keep
 * synchronized". Prerequisites: the device must provide the ability to write-
 * protect its page tables (at PAGE_SIZE granularity), and must be able to
 * recover from the resulting potential page faults.
 *
 * HMM guarantees that at any point in time, a given virtual address points to
 * either the same memory in both CPU and device page tables (that is: CPU and
 * device page tables each point to the same pages), or that one page table (CPU
 * or device) points to no entry, while the other still points to the old page
 * for the address. The latter case happens when the CPU page table update
 * happens first, and then the update is mirrored over to the device page table.
 * This does not cause any issue, because the CPU page table cannot start
 * pointing to a new page until the device page table is invalidated.
 *
 * HMM uses mmu_notifiers to monitor the CPU page tables, and forwards any
 * updates to each device driver that has registered a mirror. It also provides
 * some API calls to help with taking a snapshot of the CPU page table, and to
 * synchronize with any updates that might happen concurrently.
 *
 *
 * HMM migration to and from device memory:
 *
 * HMM provides a set of helpers to hotplug device memory as ZONE_DEVICE, with
 * a new MEMORY_DEVICE_PRIVATE type. This provides a struct page for each page
 * of the device memory, and allows the device driver to manage its memory
 * using those struct pages. Having struct pages for device memory makes
 * migration easier. Because that memory is not addressable by the CPU it must
 * never be pinned to the device; in other words, any CPU page fault can always
 * cause the device memory to be migrated (copied/moved) back to regular memory.
 *
 * A new migrate helper (migrate_vma()) has been added (see mm/migrate.c) that
 * allows use of a device DMA engine to perform the copy operation between
 * regular system memory and device memory.
 */
#ifndef LINUX_HMM_H
#define LINUX_HMM_H

#include <linux/kconfig.h>
#include <asm/pgtable.h>

#include <linux/device.h>
#include <linux/migrate.h>
#include <linux/memremap.h>
#include <linux/completion.h>
#include <linux/mmu_notifier.h>

/*
 * hmm_pfn_flag_e - HMM flag enums
 *
 * Flags:
 * HMM_PFN_VALID: pfn is valid. It has, at least, read permission.
 * HMM_PFN_WRITE: CPU page table has write permission set
 * HMM_PFN_DEVICE_PRIVATE: private device memory (ZONE_DEVICE)
 *
 * The driver provides a flags array for mapping page protections to device
 * PTE bits. If the driver valid bit for an entry is bit 3,
 * i.e., (entry & (1 << 3)), then the driver must provide
 * an array in hmm_range.flags with hmm_range.flags[HMM_PFN_VALID] == 1 << 3.
 * Same logic apply to all flags. This is the same idea as vm_page_prot in vma
 * except that this is per device driver rather than per architecture.
 */
enum hmm_pfn_flag_e {
	HMM_PFN_VALID = 0,
	HMM_PFN_WRITE,
	HMM_PFN_DEVICE_PRIVATE,
	HMM_PFN_FLAG_MAX
};

/*
 * hmm_pfn_value_e - HMM pfn special value
 *
 * Flags:
 * HMM_PFN_ERROR: corresponding CPU page table entry points to poisoned memory
 * HMM_PFN_NONE: corresponding CPU page table entry is pte_none()
 * HMM_PFN_SPECIAL: corresponding CPU page table entry is special; i.e., the
 *      result of vmf_insert_pfn() or vm_insert_page(). Therefore, it should not
 *      be mirrored by a device, because the entry will never have HMM_PFN_VALID
 *      set and the pfn value is undefined.
 *
 * Driver provides values for none entry, error entry, and special entry.
 * Driver can alias (i.e., use same value) error and special, but
 * it should not alias none with error or special.
 *
 * HMM pfn value returned by hmm_vma_get_pfns() or hmm_vma_fault() will be:
 * hmm_range.values[HMM_PFN_ERROR] if CPU page table entry is poisonous,
 * hmm_range.values[HMM_PFN_NONE] if there is no CPU page table entry,
 * hmm_range.values[HMM_PFN_SPECIAL] if CPU page table entry is a special one
 */
enum hmm_pfn_value_e {
	HMM_PFN_ERROR,
	HMM_PFN_NONE,
	HMM_PFN_SPECIAL,
	HMM_PFN_VALUE_MAX
};

/*
 * struct hmm_range - track invalidation lock on virtual address range
 *
 * @notifier: a mmu_interval_notifier that includes the start/end
 * @notifier_seq: result of mmu_interval_read_begin()
 * @hmm: the core HMM structure this range is active against
 * @vma: the vm area struct for the range
 * @list: all range lock are on a list
 * @start: range virtual start address (inclusive)
 * @end: range virtual end address (exclusive)
 * @pfns: array of pfns (big enough for the range)
 * @flags: pfn flags to match device driver page table
 * @values: pfn value for some special case (none, special, error, ...)
 * @default_flags: default flags for the range (write, read, ... see hmm doc)
 * @pfn_flags_mask: allows to mask pfn flags so that only default_flags matter
 * @pfn_shifts: pfn shift value (should be <= PAGE_SHIFT)
 * @valid: pfns array did not change since it has been fill by an HMM function
 */
struct hmm_range {
	struct mmu_interval_notifier *notifier;
	unsigned long		notifier_seq;
	unsigned long		start;
	unsigned long		end;
	uint64_t		*pfns;
	const uint64_t		*flags;
	const uint64_t		*values;
	uint64_t		default_flags;
	uint64_t		pfn_flags_mask;
	uint8_t			pfn_shift;
};

/*
 * hmm_device_entry_to_page() - return struct page pointed to by a device entry
 * @range: range use to decode device entry value
 * @entry: device entry value to get corresponding struct page from
 * Return: struct page pointer if entry is a valid, NULL otherwise
 *
 * If the device entry is valid (ie valid flag set) then return the struct page
 * matching the entry value. Otherwise return NULL.
 */
static inline struct page *hmm_device_entry_to_page(const struct hmm_range *range,
						    uint64_t entry)
{
	if (entry == range->values[HMM_PFN_NONE])
		return NULL;
	if (entry == range->values[HMM_PFN_ERROR])
		return NULL;
	if (entry == range->values[HMM_PFN_SPECIAL])
		return NULL;
	if (!(entry & range->flags[HMM_PFN_VALID]))
		return NULL;
	return pfn_to_page(entry >> range->pfn_shift);
}

/*
 * hmm_device_entry_to_pfn() - return pfn value store in a device entry
 * @range: range use to decode device entry value
 * @entry: device entry to extract pfn from
 * Return: pfn value if device entry is valid, -1UL otherwise
 */
static inline unsigned long
hmm_device_entry_to_pfn(const struct hmm_range *range, uint64_t pfn)
{
	if (pfn == range->values[HMM_PFN_NONE])
		return -1UL;
	if (pfn == range->values[HMM_PFN_ERROR])
		return -1UL;
	if (pfn == range->values[HMM_PFN_SPECIAL])
		return -1UL;
	if (!(pfn & range->flags[HMM_PFN_VALID]))
		return -1UL;
	return (pfn >> range->pfn_shift);
}

/*
 * hmm_device_entry_from_page() - create a valid device entry for a page
 * @range: range use to encode HMM pfn value
 * @page: page for which to create the device entry
 * Return: valid device entry for the page
 */
static inline uint64_t hmm_device_entry_from_page(const struct hmm_range *range,
						  struct page *page)
{
	return (page_to_pfn(page) << range->pfn_shift) |
		range->flags[HMM_PFN_VALID];
}

/*
 * hmm_device_entry_from_pfn() - create a valid device entry value from pfn
 * @range: range use to encode HMM pfn value
 * @pfn: pfn value for which to create the device entry
 * Return: valid device entry for the pfn
 */
static inline uint64_t hmm_device_entry_from_pfn(const struct hmm_range *range,
						 unsigned long pfn)
{
	return (pfn << range->pfn_shift) |
		range->flags[HMM_PFN_VALID];
}

/*
 * Retry fault if non-blocking, drop mmap_sem and return -EAGAIN in that case.
 */
#define HMM_FAULT_ALLOW_RETRY		(1 << 0)

/* Don't fault in missing PTEs, just snapshot the current state. */
#define HMM_FAULT_SNAPSHOT		(1 << 1)

#ifdef CONFIG_HMM_MIRROR
/*
 * Please see Documentation/vm/hmm.rst for how to use the range API.
 */
long hmm_range_fault(struct hmm_range *range, unsigned int flags);
#else
static inline long hmm_range_fault(struct hmm_range *range, unsigned int flags)
{
	return -EOPNOTSUPP;
}
#endif

/*
 * HMM_RANGE_DEFAULT_TIMEOUT - default timeout (ms) when waiting for a range
 *
 * When waiting for mmu notifiers we need some kind of time out otherwise we
 * could potentialy wait for ever, 1000ms ie 1s sounds like a long time to
 * wait already.
 */
#define HMM_RANGE_DEFAULT_TIMEOUT 1000

#endif /* LINUX_HMM_H */