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 #include <stdbool.h>
27 #include "vm_util.h"
28
29 #define DEFAULT_LENGTH_MB 10UL
30 #define MB_TO_BYTES(x) (x * 1024 * 1024)
31
32 #define PROTECTION (PROT_READ | PROT_WRITE | PROT_EXEC)
33 #define FLAGS (MAP_SHARED | MAP_ANONYMOUS)
34
check_bytes(char * addr)35 static void check_bytes(char *addr)
36 {
37 printf("First hex is %x\n", *((unsigned int *)addr));
38 }
39
write_bytes(char * addr,size_t len)40 static void write_bytes(char *addr, size_t len)
41 {
42 unsigned long i;
43
44 for (i = 0; i < len; i++)
45 *(addr + i) = (char)i;
46 }
47
read_bytes(char * addr,size_t len)48 static int read_bytes(char *addr, size_t len)
49 {
50 unsigned long i;
51
52 check_bytes(addr);
53 for (i = 0; i < len; i++)
54 if (*(addr + i) != (char)i) {
55 printf("Mismatch at %lu\n", i);
56 return 1;
57 }
58 return 0;
59 }
60
register_region_with_uffd(char * addr,size_t len)61 static void register_region_with_uffd(char *addr, size_t len)
62 {
63 long uffd; /* userfaultfd file descriptor */
64 struct uffdio_api uffdio_api;
65
66 /* Create and enable userfaultfd object. */
67
68 uffd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK);
69 if (uffd == -1) {
70 perror("userfaultfd");
71 exit(1);
72 }
73
74 uffdio_api.api = UFFD_API;
75 uffdio_api.features = 0;
76 if (ioctl(uffd, UFFDIO_API, &uffdio_api) == -1) {
77 perror("ioctl-UFFDIO_API");
78 exit(1);
79 }
80
81 /* Create a private anonymous mapping. The memory will be
82 * demand-zero paged--that is, not yet allocated. When we
83 * actually touch the memory, it will be allocated via
84 * the userfaultfd.
85 */
86
87 addr = mmap(NULL, len, PROT_READ | PROT_WRITE,
88 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
89 if (addr == MAP_FAILED) {
90 perror("mmap");
91 exit(1);
92 }
93
94 printf("Address returned by mmap() = %p\n", addr);
95
96 /* Register the memory range of the mapping we just created for
97 * handling by the userfaultfd object. In mode, we request to track
98 * missing pages (i.e., pages that have not yet been faulted in).
99 */
100 if (uffd_register(uffd, addr, len, true, false, false)) {
101 perror("ioctl-UFFDIO_REGISTER");
102 exit(1);
103 }
104 }
105
main(int argc,char * argv[])106 int main(int argc, char *argv[])
107 {
108 size_t length = 0;
109 int ret = 0, fd;
110
111 if (argc >= 2 && !strcmp(argv[1], "-h")) {
112 printf("Usage: %s [length_in_MB]\n", argv[0]);
113 exit(1);
114 }
115
116 /* Read memory length as the first arg if valid, otherwise fallback to
117 * the default length.
118 */
119 if (argc >= 2)
120 length = (size_t)atoi(argv[1]);
121 else
122 length = DEFAULT_LENGTH_MB;
123
124 length = MB_TO_BYTES(length);
125 fd = memfd_create(argv[0], MFD_HUGETLB);
126 if (fd < 0) {
127 perror("Open failed");
128 exit(1);
129 }
130
131 /* mmap to a PUD aligned address to hopefully trigger pmd sharing. */
132 unsigned long suggested_addr = 0x7eaa40000000;
133 void *haddr = mmap((void *)suggested_addr, length, PROTECTION,
134 MAP_HUGETLB | MAP_SHARED | MAP_POPULATE, fd, 0);
135 printf("Map haddr: Returned address is %p\n", haddr);
136 if (haddr == MAP_FAILED) {
137 perror("mmap1");
138 exit(1);
139 }
140
141 /* mmap again to a dummy address to hopefully trigger pmd sharing. */
142 suggested_addr = 0x7daa40000000;
143 void *daddr = mmap((void *)suggested_addr, length, PROTECTION,
144 MAP_HUGETLB | MAP_SHARED | MAP_POPULATE, fd, 0);
145 printf("Map daddr: Returned address is %p\n", daddr);
146 if (daddr == MAP_FAILED) {
147 perror("mmap3");
148 exit(1);
149 }
150
151 suggested_addr = 0x7faa40000000;
152 void *vaddr =
153 mmap((void *)suggested_addr, length, PROTECTION, FLAGS, -1, 0);
154 printf("Map vaddr: Returned address is %p\n", vaddr);
155 if (vaddr == MAP_FAILED) {
156 perror("mmap2");
157 exit(1);
158 }
159
160 register_region_with_uffd(haddr, length);
161
162 void *addr = mremap(haddr, length, length,
163 MREMAP_MAYMOVE | MREMAP_FIXED, vaddr);
164 if (addr == MAP_FAILED) {
165 perror("mremap");
166 exit(1);
167 }
168
169 printf("Mremap: Returned address is %p\n", addr);
170 check_bytes(addr);
171 write_bytes(addr, length);
172 ret = read_bytes(addr, length);
173
174 munmap(addr, length);
175
176 addr = mremap(addr, length, length, 0);
177 if (addr != MAP_FAILED) {
178 printf("mremap: Expected failure, but call succeeded\n");
179 exit(1);
180 }
181
182 close(fd);
183
184 return ret;
185 }
186