1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * hugepage-mmap:
4  *
5  * Example of using huge page memory in a user application using the mmap
6  * system call.  Before running this application, make sure that the
7  * administrator has mounted the hugetlbfs filesystem (on some directory
8  * like /mnt) using the command mount -t hugetlbfs nodev /mnt. In this
9  * example, the app is requesting memory of size 256MB that is backed by
10  * huge pages.
11  *
12  * For the ia64 architecture, the Linux kernel reserves Region number 4 for
13  * huge pages.  That means that if one requires a fixed address, a huge page
14  * aligned address starting with 0x800000... will be required.  If a fixed
15  * address is not required, the kernel will select an address in the proper
16  * range.
17  * Other architectures, such as ppc64, i386 or x86_64 are not so constrained.
18  */
19 #define _GNU_SOURCE
20 #include <stdlib.h>
21 #include <stdio.h>
22 #include <unistd.h>
23 #include <sys/mman.h>
24 #include <fcntl.h>
25 
26 #define LENGTH (256UL*1024*1024)
27 #define PROTECTION (PROT_READ | PROT_WRITE)
28 
29 /* Only ia64 requires this */
30 #ifdef __ia64__
31 #define ADDR (void *)(0x8000000000000000UL)
32 #define FLAGS (MAP_SHARED | MAP_FIXED)
33 #else
34 #define ADDR (void *)(0x0UL)
35 #define FLAGS (MAP_SHARED)
36 #endif
37 
38 static void check_bytes(char *addr)
39 {
40 	printf("First hex is %x\n", *((unsigned int *)addr));
41 }
42 
43 static void write_bytes(char *addr)
44 {
45 	unsigned long i;
46 
47 	for (i = 0; i < LENGTH; i++)
48 		*(addr + i) = (char)i;
49 }
50 
51 static int read_bytes(char *addr)
52 {
53 	unsigned long i;
54 
55 	check_bytes(addr);
56 	for (i = 0; i < LENGTH; i++)
57 		if (*(addr + i) != (char)i) {
58 			printf("Mismatch at %lu\n", i);
59 			return 1;
60 		}
61 	return 0;
62 }
63 
64 int main(void)
65 {
66 	void *addr;
67 	int fd, ret;
68 
69 	fd = memfd_create("hugepage-mmap", MFD_HUGETLB);
70 	if (fd < 0) {
71 		perror("memfd_create() failed");
72 		exit(1);
73 	}
74 
75 	addr = mmap(ADDR, LENGTH, PROTECTION, FLAGS, fd, 0);
76 	if (addr == MAP_FAILED) {
77 		perror("mmap");
78 		close(fd);
79 		exit(1);
80 	}
81 
82 	printf("Returned address is %p\n", addr);
83 	check_bytes(addr);
84 	write_bytes(addr);
85 	ret = read_bytes(addr);
86 
87 	munmap(addr, LENGTH);
88 	close(fd);
89 
90 	return ret;
91 }
92