1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * hugepage-mremap:
4 *
5 * Example of remapping huge page memory in a user application using the
6 * mremap system call. The path to a file in a hugetlbfs filesystem must
7 * be passed as the last argument to this test. The amount of memory used
8 * by this test in MBs can optionally be passed as an argument. If no memory
9 * amount is passed, the default amount is 10MB.
10 *
11 * To make sure the test triggers pmd sharing and goes through the 'unshare'
12 * path in the mremap code use 1GB (1024) or more.
13 */
14
15 #define _GNU_SOURCE
16 #include <stdlib.h>
17 #include <stdio.h>
18 #include <unistd.h>
19 #include <sys/mman.h>
20 #include <errno.h>
21 #include <fcntl.h> /* Definition of O_* constants */
22 #include <sys/syscall.h> /* Definition of SYS_* constants */
23 #include <linux/userfaultfd.h>
24 #include <sys/ioctl.h>
25 #include <string.h>
26
27 #define DEFAULT_LENGTH_MB 10UL
28 #define MB_TO_BYTES(x) (x * 1024 * 1024)
29
30 #define PROTECTION (PROT_READ | PROT_WRITE | PROT_EXEC)
31 #define FLAGS (MAP_SHARED | MAP_ANONYMOUS)
32
check_bytes(char * addr)33 static void check_bytes(char *addr)
34 {
35 printf("First hex is %x\n", *((unsigned int *)addr));
36 }
37
write_bytes(char * addr,size_t len)38 static void write_bytes(char *addr, size_t len)
39 {
40 unsigned long i;
41
42 for (i = 0; i < len; i++)
43 *(addr + i) = (char)i;
44 }
45
read_bytes(char * addr,size_t len)46 static int read_bytes(char *addr, size_t len)
47 {
48 unsigned long i;
49
50 check_bytes(addr);
51 for (i = 0; i < len; i++)
52 if (*(addr + i) != (char)i) {
53 printf("Mismatch at %lu\n", i);
54 return 1;
55 }
56 return 0;
57 }
58
register_region_with_uffd(char * addr,size_t len)59 static void register_region_with_uffd(char *addr, size_t len)
60 {
61 long uffd; /* userfaultfd file descriptor */
62 struct uffdio_api uffdio_api;
63 struct uffdio_register uffdio_register;
64
65 /* Create and enable userfaultfd object. */
66
67 uffd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK);
68 if (uffd == -1) {
69 perror("userfaultfd");
70 exit(1);
71 }
72
73 uffdio_api.api = UFFD_API;
74 uffdio_api.features = 0;
75 if (ioctl(uffd, UFFDIO_API, &uffdio_api) == -1) {
76 perror("ioctl-UFFDIO_API");
77 exit(1);
78 }
79
80 /* Create a private anonymous mapping. The memory will be
81 * demand-zero paged--that is, not yet allocated. When we
82 * actually touch the memory, it will be allocated via
83 * the userfaultfd.
84 */
85
86 addr = mmap(NULL, len, PROT_READ | PROT_WRITE,
87 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
88 if (addr == MAP_FAILED) {
89 perror("mmap");
90 exit(1);
91 }
92
93 printf("Address returned by mmap() = %p\n", addr);
94
95 /* Register the memory range of the mapping we just created for
96 * handling by the userfaultfd object. In mode, we request to track
97 * missing pages (i.e., pages that have not yet been faulted in).
98 */
99
100 uffdio_register.range.start = (unsigned long)addr;
101 uffdio_register.range.len = len;
102 uffdio_register.mode = UFFDIO_REGISTER_MODE_MISSING;
103 if (ioctl(uffd, UFFDIO_REGISTER, &uffdio_register) == -1) {
104 perror("ioctl-UFFDIO_REGISTER");
105 exit(1);
106 }
107 }
108
main(int argc,char * argv[])109 int main(int argc, char *argv[])
110 {
111 size_t length = 0;
112 int ret = 0, fd;
113
114 if (argc >= 2 && !strcmp(argv[1], "-h")) {
115 printf("Usage: %s [length_in_MB]\n", argv[0]);
116 exit(1);
117 }
118
119 /* Read memory length as the first arg if valid, otherwise fallback to
120 * the default length.
121 */
122 if (argc >= 2)
123 length = (size_t)atoi(argv[1]);
124 else
125 length = DEFAULT_LENGTH_MB;
126
127 length = MB_TO_BYTES(length);
128 fd = memfd_create(argv[0], MFD_HUGETLB);
129 if (fd < 0) {
130 perror("Open failed");
131 exit(1);
132 }
133
134 /* mmap to a PUD aligned address to hopefully trigger pmd sharing. */
135 unsigned long suggested_addr = 0x7eaa40000000;
136 void *haddr = mmap((void *)suggested_addr, length, PROTECTION,
137 MAP_HUGETLB | MAP_SHARED | MAP_POPULATE, fd, 0);
138 printf("Map haddr: Returned address is %p\n", haddr);
139 if (haddr == MAP_FAILED) {
140 perror("mmap1");
141 exit(1);
142 }
143
144 /* mmap again to a dummy address to hopefully trigger pmd sharing. */
145 suggested_addr = 0x7daa40000000;
146 void *daddr = mmap((void *)suggested_addr, length, PROTECTION,
147 MAP_HUGETLB | MAP_SHARED | MAP_POPULATE, fd, 0);
148 printf("Map daddr: Returned address is %p\n", daddr);
149 if (daddr == MAP_FAILED) {
150 perror("mmap3");
151 exit(1);
152 }
153
154 suggested_addr = 0x7faa40000000;
155 void *vaddr =
156 mmap((void *)suggested_addr, length, PROTECTION, FLAGS, -1, 0);
157 printf("Map vaddr: Returned address is %p\n", vaddr);
158 if (vaddr == MAP_FAILED) {
159 perror("mmap2");
160 exit(1);
161 }
162
163 register_region_with_uffd(haddr, length);
164
165 void *addr = mremap(haddr, length, length,
166 MREMAP_MAYMOVE | MREMAP_FIXED, vaddr);
167 if (addr == MAP_FAILED) {
168 perror("mremap");
169 exit(1);
170 }
171
172 printf("Mremap: Returned address is %p\n", addr);
173 check_bytes(addr);
174 write_bytes(addr, length);
175 ret = read_bytes(addr, length);
176
177 munmap(addr, length);
178
179 addr = mremap(addr, length, length, 0);
180 if (addr != MAP_FAILED) {
181 printf("mremap: Expected failure, but call succeeded\n");
182 exit(1);
183 }
184
185 close(fd);
186
187 return ret;
188 }
189