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
35static void check_bytes(char *addr)
36{
37	printf("First hex is %x\n", *((unsigned int *)addr));
38}
39
40static 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
48static 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
61static 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
106int 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