summaryrefslogtreecommitdiff
path: root/tools/testing/selftests/vm/mremap_dontunmap.c
blob: ee06cb0b9efbe0db7cff51ad081201fd46da786f (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
// SPDX-License-Identifier: GPL-2.0

/*
 * Tests for mremap w/ MREMAP_DONTUNMAP.
 *
 * Copyright 2020, Brian Geffon <bgeffon@google.com>
 */
#define _GNU_SOURCE
#include <sys/mman.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>

#include "../kselftest.h"

#ifndef MREMAP_DONTUNMAP
#define MREMAP_DONTUNMAP 4
#endif

unsigned long page_size;
char *page_buffer;

static void dump_maps(void)
{
	char cmd[32];

	snprintf(cmd, sizeof(cmd), "cat /proc/%d/maps", getpid());
	system(cmd);
}

#define BUG_ON(condition, description)					      \
	do {								      \
		if (condition) {					      \
			fprintf(stderr, "[FAIL]\t%s():%d\t%s:%s\n", __func__, \
				__LINE__, (description), strerror(errno));    \
			dump_maps();					  \
			exit(1);					      \
		} 							      \
	} while (0)

// Try a simple operation for to "test" for kernel support this prevents
// reporting tests as failed when it's run on an older kernel.
static int kernel_support_for_mremap_dontunmap()
{
	int ret = 0;
	unsigned long num_pages = 1;
	void *source_mapping = mmap(NULL, num_pages * page_size, PROT_NONE,
				    MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
	BUG_ON(source_mapping == MAP_FAILED, "mmap");

	// This simple remap should only fail if MREMAP_DONTUNMAP isn't
	// supported.
	void *dest_mapping =
	    mremap(source_mapping, num_pages * page_size, num_pages * page_size,
		   MREMAP_DONTUNMAP | MREMAP_MAYMOVE, 0);
	if (dest_mapping == MAP_FAILED) {
		ret = errno;
	} else {
		BUG_ON(munmap(dest_mapping, num_pages * page_size) == -1,
		       "unable to unmap destination mapping");
	}

	BUG_ON(munmap(source_mapping, num_pages * page_size) == -1,
	       "unable to unmap source mapping");
	return ret;
}

// This helper will just validate that an entire mapping contains the expected
// byte.
static int check_region_contains_byte(void *addr, unsigned long size, char byte)
{
	BUG_ON(size & (page_size - 1),
	       "check_region_contains_byte expects page multiples");
	BUG_ON((unsigned long)addr & (page_size - 1),
	       "check_region_contains_byte expects page alignment");

	memset(page_buffer, byte, page_size);

	unsigned long num_pages = size / page_size;
	unsigned long i;

	// Compare each page checking that it contains our expected byte.
	for (i = 0; i < num_pages; ++i) {
		int ret =
		    memcmp(addr + (i * page_size), page_buffer, page_size);
		if (ret) {
			return ret;
		}
	}

	return 0;
}

// this test validates that MREMAP_DONTUNMAP moves the pagetables while leaving
// the source mapping mapped.
static void mremap_dontunmap_simple()
{
	unsigned long num_pages = 5;

	void *source_mapping =
	    mmap(NULL, num_pages * page_size, PROT_READ | PROT_WRITE,
		 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
	BUG_ON(source_mapping == MAP_FAILED, "mmap");

	memset(source_mapping, 'a', num_pages * page_size);

	// Try to just move the whole mapping anywhere (not fixed).
	void *dest_mapping =
	    mremap(source_mapping, num_pages * page_size, num_pages * page_size,
		   MREMAP_DONTUNMAP | MREMAP_MAYMOVE, NULL);
	BUG_ON(dest_mapping == MAP_FAILED, "mremap");

	// Validate that the pages have been moved, we know they were moved if
	// the dest_mapping contains a's.
	BUG_ON(check_region_contains_byte
	       (dest_mapping, num_pages * page_size, 'a') != 0,
	       "pages did not migrate");
	BUG_ON(check_region_contains_byte
	       (source_mapping, num_pages * page_size, 0) != 0,
	       "source should have no ptes");

	BUG_ON(munmap(dest_mapping, num_pages * page_size) == -1,
	       "unable to unmap destination mapping");
	BUG_ON(munmap(source_mapping, num_pages * page_size) == -1,
	       "unable to unmap source mapping");
}

// This test validates MREMAP_DONTUNMAP will move page tables to a specific
// destination using MREMAP_FIXED, also while validating that the source
// remains intact.
static void mremap_dontunmap_simple_fixed()
{
	unsigned long num_pages = 5;

	// Since we want to guarantee that we can remap to a point, we will
	// create a mapping up front.
	void *dest_mapping =
	    mmap(NULL, num_pages * page_size, PROT_READ | PROT_WRITE,
		 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
	BUG_ON(dest_mapping == MAP_FAILED, "mmap");
	memset(dest_mapping, 'X', num_pages * page_size);

	void *source_mapping =
	    mmap(NULL, num_pages * page_size, PROT_READ | PROT_WRITE,
		 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
	BUG_ON(source_mapping == MAP_FAILED, "mmap");
	memset(source_mapping, 'a', num_pages * page_size);

	void *remapped_mapping =
	    mremap(source_mapping, num_pages * page_size, num_pages * page_size,
		   MREMAP_FIXED | MREMAP_DONTUNMAP | MREMAP_MAYMOVE,
		   dest_mapping);
	BUG_ON(remapped_mapping == MAP_FAILED, "mremap");
	BUG_ON(remapped_mapping != dest_mapping,
	       "mremap should have placed the remapped mapping at dest_mapping");

	// The dest mapping will have been unmap by mremap so we expect the Xs
	// to be gone and replaced with a's.
	BUG_ON(check_region_contains_byte
	       (dest_mapping, num_pages * page_size, 'a') != 0,
	       "pages did not migrate");

	// And the source mapping will have had its ptes dropped.
	BUG_ON(check_region_contains_byte
	       (source_mapping, num_pages * page_size, 0) != 0,
	       "source should have no ptes");

	BUG_ON(munmap(dest_mapping, num_pages * page_size) == -1,
	       "unable to unmap destination mapping");
	BUG_ON(munmap(source_mapping, num_pages * page_size) == -1,
	       "unable to unmap source mapping");
}

// This test validates that we can MREMAP_DONTUNMAP for a portion of an
// existing mapping.
static void mremap_dontunmap_partial_mapping()
{
	/*
	 *  source mapping:
	 *  --------------
	 *  | aaaaaaaaaa |
	 *  --------------
	 *  to become:
	 *  --------------
	 *  | aaaaa00000 |
	 *  --------------
	 *  With the destination mapping containing 5 pages of As.
	 *  ---------
	 *  | aaaaa |
	 *  ---------
	 */
	unsigned long num_pages = 10;
	void *source_mapping =
	    mmap(NULL, num_pages * page_size, PROT_READ | PROT_WRITE,
		 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
	BUG_ON(source_mapping == MAP_FAILED, "mmap");
	memset(source_mapping, 'a', num_pages * page_size);

	// We will grab the last 5 pages of the source and move them.
	void *dest_mapping =
	    mremap(source_mapping + (5 * page_size), 5 * page_size,
		   5 * page_size,
		   MREMAP_DONTUNMAP | MREMAP_MAYMOVE, NULL);
	BUG_ON(dest_mapping == MAP_FAILED, "mremap");

	// We expect the first 5 pages of the source to contain a's and the
	// final 5 pages to contain zeros.
	BUG_ON(check_region_contains_byte(source_mapping, 5 * page_size, 'a') !=
	       0, "first 5 pages of source should have original pages");
	BUG_ON(check_region_contains_byte
	       (source_mapping + (5 * page_size), 5 * page_size, 0) != 0,
	       "final 5 pages of source should have no ptes");

	// Finally we expect the destination to have 5 pages worth of a's.
	BUG_ON(check_region_contains_byte(dest_mapping, 5 * page_size, 'a') !=
	       0, "dest mapping should contain ptes from the source");

	BUG_ON(munmap(dest_mapping, 5 * page_size) == -1,
	       "unable to unmap destination mapping");
	BUG_ON(munmap(source_mapping, num_pages * page_size) == -1,
	       "unable to unmap source mapping");
}

// This test validates that we can remap over only a portion of a mapping.
static void mremap_dontunmap_partial_mapping_overwrite(void)
{
	/*
	 *  source mapping:
	 *  ---------
	 *  |aaaaa|
	 *  ---------
	 *  dest mapping initially:
	 *  -----------
	 *  |XXXXXXXXXX|
	 *  ------------
	 *  Source to become:
	 *  ---------
	 *  |00000|
	 *  ---------
	 *  With the destination mapping containing 5 pages of As.
	 *  ------------
	 *  |aaaaaXXXXX|
	 *  ------------
	 */
	void *source_mapping =
	    mmap(NULL, 5 * page_size, PROT_READ | PROT_WRITE,
		 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
	BUG_ON(source_mapping == MAP_FAILED, "mmap");
	memset(source_mapping, 'a', 5 * page_size);

	void *dest_mapping =
	    mmap(NULL, 10 * page_size, PROT_READ | PROT_WRITE,
		 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
	BUG_ON(dest_mapping == MAP_FAILED, "mmap");
	memset(dest_mapping, 'X', 10 * page_size);

	// We will grab the last 5 pages of the source and move them.
	void *remapped_mapping =
	    mremap(source_mapping, 5 * page_size,
		   5 * page_size,
		   MREMAP_DONTUNMAP | MREMAP_MAYMOVE | MREMAP_FIXED, dest_mapping);
	BUG_ON(dest_mapping == MAP_FAILED, "mremap");
	BUG_ON(dest_mapping != remapped_mapping, "expected to remap to dest_mapping");

	BUG_ON(check_region_contains_byte(source_mapping, 5 * page_size, 0) !=
	       0, "first 5 pages of source should have no ptes");

	// Finally we expect the destination to have 5 pages worth of a's.
	BUG_ON(check_region_contains_byte(dest_mapping, 5 * page_size, 'a') != 0,
			"dest mapping should contain ptes from the source");

	// Finally the last 5 pages shouldn't have been touched.
	BUG_ON(check_region_contains_byte(dest_mapping + (5 * page_size),
				5 * page_size, 'X') != 0,
			"dest mapping should have retained the last 5 pages");

	BUG_ON(munmap(dest_mapping, 10 * page_size) == -1,
	       "unable to unmap destination mapping");
	BUG_ON(munmap(source_mapping, 5 * page_size) == -1,
	       "unable to unmap source mapping");
}

int main(void)
{
	page_size = sysconf(_SC_PAGE_SIZE);

	// test for kernel support for MREMAP_DONTUNMAP skipping the test if
	// not.
	if (kernel_support_for_mremap_dontunmap() != 0) {
		printf("No kernel support for MREMAP_DONTUNMAP\n");
		return KSFT_SKIP;
	}

	// Keep a page sized buffer around for when we need it.
	page_buffer =
	    mmap(NULL, page_size, PROT_READ | PROT_WRITE,
		 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
	BUG_ON(page_buffer == MAP_FAILED, "unable to mmap a page.");

	mremap_dontunmap_simple();
	mremap_dontunmap_simple_fixed();
	mremap_dontunmap_partial_mapping();
	mremap_dontunmap_partial_mapping_overwrite();

	BUG_ON(munmap(page_buffer, page_size) == -1,
	       "unable to unmap page buffer");

	printf("OK\n");
	return 0;
}