aboutsummaryrefslogtreecommitdiff
path: root/util/userfaultfd.c
blob: 1b2fa949d4d084fd42c2fa91fdcd4f1e4e864b39 (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
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
/*
 * Linux UFFD-WP support
 *
 * Copyright Virtuozzo GmbH, 2020
 *
 * Authors:
 *  Andrey Gruzdev   <andrey.gruzdev@virtuozzo.com>
 *
 * This work is licensed under the terms of the GNU GPL, version 2 or
 * later.  See the COPYING file in the top-level directory.
 */

#include "qemu/osdep.h"
#include "qemu/bitops.h"
#include "qemu/error-report.h"
#include "qemu/userfaultfd.h"
#include "trace.h"
#include <poll.h>
#include <sys/syscall.h>
#include <sys/ioctl.h>

typedef enum {
    UFFD_UNINITIALIZED = 0,
    UFFD_USE_DEV_PATH,
    UFFD_USE_SYSCALL,
} uffd_open_mode;

int uffd_open(int flags)
{
#if defined(__NR_userfaultfd)
    static uffd_open_mode open_mode;
    static int uffd_dev;

    /* Detect how to generate uffd desc when run the 1st time */
    if (open_mode == UFFD_UNINITIALIZED) {
        /*
         * Make /dev/userfaultfd the default approach because it has better
         * permission controls, meanwhile allows kernel faults without any
         * privilege requirement (e.g. SYS_CAP_PTRACE).
         */
        uffd_dev = open("/dev/userfaultfd", O_RDWR | O_CLOEXEC);
        if (uffd_dev >= 0) {
            open_mode = UFFD_USE_DEV_PATH;
        } else {
            /* Fallback to the system call */
            open_mode = UFFD_USE_SYSCALL;
        }
        trace_uffd_detect_open_mode(open_mode);
    }

    if (open_mode == UFFD_USE_DEV_PATH) {
        assert(uffd_dev >= 0);
        return ioctl(uffd_dev, USERFAULTFD_IOC_NEW, flags);
    }

    return syscall(__NR_userfaultfd, flags);
#else
    return -EINVAL;
#endif
}

/**
 * uffd_query_features: query UFFD features
 *
 * Returns: 0 on success, negative value in case of an error
 *
 * @features: parameter to receive 'uffdio_api.features'
 */
int uffd_query_features(uint64_t *features)
{
    int uffd_fd;
    struct uffdio_api api_struct = { 0 };
    int ret = -1;

    uffd_fd = uffd_open(O_CLOEXEC);
    if (uffd_fd < 0) {
        trace_uffd_query_features_nosys(errno);
        return -1;
    }

    api_struct.api = UFFD_API;
    api_struct.features = 0;

    if (ioctl(uffd_fd, UFFDIO_API, &api_struct)) {
        trace_uffd_query_features_api_failed(errno);
        goto out;
    }
    *features = api_struct.features;
    ret = 0;

out:
    close(uffd_fd);
    return ret;
}

/**
 * uffd_create_fd: create UFFD file descriptor
 *
 * Returns non-negative file descriptor or negative value in case of an error
 *
 * @features: UFFD features to request
 * @non_blocking: create UFFD file descriptor for non-blocking operation
 */
int uffd_create_fd(uint64_t features, bool non_blocking)
{
    int uffd_fd;
    int flags;
    struct uffdio_api api_struct = { 0 };
    uint64_t ioctl_mask = BIT(_UFFDIO_REGISTER) | BIT(_UFFDIO_UNREGISTER);

    flags = O_CLOEXEC | (non_blocking ? O_NONBLOCK : 0);
    uffd_fd = uffd_open(flags);
    if (uffd_fd < 0) {
        trace_uffd_create_fd_nosys(errno);
        return -1;
    }

    api_struct.api = UFFD_API;
    api_struct.features = features;
    if (ioctl(uffd_fd, UFFDIO_API, &api_struct)) {
        trace_uffd_create_fd_api_failed(errno);
        goto fail;
    }
    if ((api_struct.ioctls & ioctl_mask) != ioctl_mask) {
        trace_uffd_create_fd_api_noioctl(ioctl_mask, api_struct.ioctls);
        goto fail;
    }

    return uffd_fd;

fail:
    close(uffd_fd);
    return -1;
}

/**
 * uffd_close_fd: close UFFD file descriptor
 *
 * @uffd_fd: UFFD file descriptor
 */
void uffd_close_fd(int uffd_fd)
{
    assert(uffd_fd >= 0);
    close(uffd_fd);
}

/**
 * uffd_register_memory: register memory range via UFFD-IO
 *
 * Returns 0 in case of success, negative value in case of an error
 *
 * @uffd_fd: UFFD file descriptor
 * @addr: base address of memory range
 * @length: length of memory range
 * @mode: UFFD register mode (UFFDIO_REGISTER_MODE_MISSING, ...)
 * @ioctls: optional pointer to receive supported IOCTL mask
 */
int uffd_register_memory(int uffd_fd, void *addr, uint64_t length,
        uint64_t mode, uint64_t *ioctls)
{
    struct uffdio_register uffd_register;

    uffd_register.range.start = (uintptr_t) addr;
    uffd_register.range.len = length;
    uffd_register.mode = mode;

    if (ioctl(uffd_fd, UFFDIO_REGISTER, &uffd_register)) {
        trace_uffd_register_memory_failed(addr, length, mode, errno);
        return -1;
    }
    if (ioctls) {
        *ioctls = uffd_register.ioctls;
    }

    return 0;
}

/**
 * uffd_unregister_memory: un-register memory range with UFFD-IO
 *
 * Returns 0 in case of success, negative value in case of an error
 *
 * @uffd_fd: UFFD file descriptor
 * @addr: base address of memory range
 * @length: length of memory range
 */
int uffd_unregister_memory(int uffd_fd, void *addr, uint64_t length)
{
    struct uffdio_range uffd_range;

    uffd_range.start = (uintptr_t) addr;
    uffd_range.len = length;

    if (ioctl(uffd_fd, UFFDIO_UNREGISTER, &uffd_range)) {
        trace_uffd_unregister_memory_failed(addr, length, errno);
        return -1;
    }

    return 0;
}

/**
 * uffd_change_protection: protect/un-protect memory range for writes via UFFD-IO
 *
 * Returns 0 on success, negative value in case of error
 *
 * @uffd_fd: UFFD file descriptor
 * @addr: base address of memory range
 * @length: length of memory range
 * @wp: write-protect/unprotect
 * @dont_wake: do not wake threads waiting on wr-protected page
 */
int uffd_change_protection(int uffd_fd, void *addr, uint64_t length,
        bool wp, bool dont_wake)
{
    struct uffdio_writeprotect uffd_writeprotect;

    uffd_writeprotect.range.start = (uintptr_t) addr;
    uffd_writeprotect.range.len = length;
    if (!wp && dont_wake) {
        /* DONTWAKE is meaningful only on protection release */
        uffd_writeprotect.mode = UFFDIO_WRITEPROTECT_MODE_DONTWAKE;
    } else {
        uffd_writeprotect.mode = (wp ? UFFDIO_WRITEPROTECT_MODE_WP : 0);
    }

    if (ioctl(uffd_fd, UFFDIO_WRITEPROTECT, &uffd_writeprotect)) {
        error_report("uffd_change_protection() failed: addr=%p len=%" PRIu64
                " mode=%" PRIx64 " errno=%i", addr, length,
                (uint64_t) uffd_writeprotect.mode, errno);
        return -1;
    }

    return 0;
}

/**
 * uffd_copy_page: copy range of pages to destination via UFFD-IO
 *
 * Copy range of source pages to the destination to resolve
 * missing page fault somewhere in the destination range.
 *
 * Returns 0 on success, negative value in case of an error
 *
 * @uffd_fd: UFFD file descriptor
 * @dst_addr: destination base address
 * @src_addr: source base address
 * @length: length of the range to copy
 * @dont_wake: do not wake threads waiting on missing page
 */
int uffd_copy_page(int uffd_fd, void *dst_addr, void *src_addr,
        uint64_t length, bool dont_wake)
{
    struct uffdio_copy uffd_copy;

    uffd_copy.dst = (uintptr_t) dst_addr;
    uffd_copy.src = (uintptr_t) src_addr;
    uffd_copy.len = length;
    uffd_copy.mode = dont_wake ? UFFDIO_COPY_MODE_DONTWAKE : 0;

    if (ioctl(uffd_fd, UFFDIO_COPY, &uffd_copy)) {
        error_report("uffd_copy_page() failed: dst_addr=%p src_addr=%p length=%" PRIu64
                " mode=%" PRIx64 " errno=%i", dst_addr, src_addr,
                length, (uint64_t) uffd_copy.mode, errno);
        return -1;
    }

    return 0;
}

/**
 * uffd_zero_page: fill range of pages with zeroes via UFFD-IO
 *
 * Fill range pages with zeroes to resolve missing page fault within the range.
 *
 * Returns 0 on success, negative value in case of an error
 *
 * @uffd_fd: UFFD file descriptor
 * @addr: base address
 * @length: length of the range to fill with zeroes
 * @dont_wake: do not wake threads waiting on missing page
 */
int uffd_zero_page(int uffd_fd, void *addr, uint64_t length, bool dont_wake)
{
    struct uffdio_zeropage uffd_zeropage;

    uffd_zeropage.range.start = (uintptr_t) addr;
    uffd_zeropage.range.len = length;
    uffd_zeropage.mode = dont_wake ? UFFDIO_ZEROPAGE_MODE_DONTWAKE : 0;

    if (ioctl(uffd_fd, UFFDIO_ZEROPAGE, &uffd_zeropage)) {
        error_report("uffd_zero_page() failed: addr=%p length=%" PRIu64
                " mode=%" PRIx64 " errno=%i", addr, length,
                (uint64_t) uffd_zeropage.mode, errno);
        return -1;
    }

    return 0;
}

/**
 * uffd_wakeup: wake up threads waiting on page UFFD-managed page fault resolution
 *
 * Wake up threads waiting on any page/pages from the designated range.
 * The main use case is when during some period, page faults are resolved
 * via UFFD-IO IOCTLs with MODE_DONTWAKE flag set, then after that all waits
 * for the whole memory range are satisfied in a single call to uffd_wakeup().
 *
 * Returns 0 on success, negative value in case of an error
 *
 * @uffd_fd: UFFD file descriptor
 * @addr: base address
 * @length: length of the range
 */
int uffd_wakeup(int uffd_fd, void *addr, uint64_t length)
{
    struct uffdio_range uffd_range;

    uffd_range.start = (uintptr_t) addr;
    uffd_range.len = length;

    if (ioctl(uffd_fd, UFFDIO_WAKE, &uffd_range)) {
        error_report("uffd_wakeup() failed: addr=%p length=%" PRIu64 " errno=%i",
                addr, length, errno);
        return -1;
    }

    return 0;
}

/**
 * uffd_read_events: read pending UFFD events
 *
 * Returns number of fetched messages, 0 if non is available or
 * negative value in case of an error
 *
 * @uffd_fd: UFFD file descriptor
 * @msgs: pointer to message buffer
 * @count: number of messages that can fit in the buffer
 */
int uffd_read_events(int uffd_fd, struct uffd_msg *msgs, int count)
{
    ssize_t res;
    do {
        res = read(uffd_fd, msgs, count * sizeof(struct uffd_msg));
    } while (res < 0 && errno == EINTR);

    if ((res < 0 && errno == EAGAIN)) {
        return 0;
    }
    if (res < 0) {
        error_report("uffd_read_events() failed: errno=%i", errno);
        return -1;
    }

    return (int) (res / sizeof(struct uffd_msg));
}

/**
 * uffd_poll_events: poll UFFD file descriptor for read
 *
 * Returns true if events are available for read, false otherwise
 *
 * @uffd_fd: UFFD file descriptor
 * @tmo: timeout value
 */
bool uffd_poll_events(int uffd_fd, int tmo)
{
    int res;
    struct pollfd poll_fd = { .fd = uffd_fd, .events = POLLIN, .revents = 0 };

    do {
        res = poll(&poll_fd, 1, tmo);
    } while (res < 0 && errno == EINTR);

    if (res == 0) {
        return false;
    }
    if (res < 0) {
        error_report("uffd_poll_events() failed: errno=%i", errno);
        return false;
    }

    return (poll_fd.revents & POLLIN) != 0;
}