1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * Example of using hugepage memory in a user application using the mmap
4  * system call with MAP_HUGETLB flag.  Before running this program make
5  * sure the administrator has allocated enough default sized huge pages
6  * to cover the 256 MB allocation.
7  *
8  * For ia64 architecture, Linux kernel reserves Region number 4 for hugepages.
9  * That means the addresses starting with 0x800000... will need to be
10  * specified.  Specifying a fixed address is not required on ppc64, i386
11  * or x86_64.
12  */
13 #include <stdlib.h>
14 #include <stdio.h>
15 #include <unistd.h>
16 #include <sys/mman.h>
17 #include <fcntl.h>
18 
19 #define LENGTH (256UL*1024*1024)
20 #define PROTECTION (PROT_READ | PROT_WRITE)
21 
22 /* Only ia64 requires this */
23 #ifdef __ia64__
24 #define ADDR (void *)(0x8000000000000000UL)
25 #define FLAGS (MAP_PRIVATE | MAP_ANONYMOUS | MAP_HUGETLB | MAP_FIXED)
26 #else
27 #define ADDR (void *)(0x0UL)
28 #define FLAGS (MAP_PRIVATE | MAP_ANONYMOUS | MAP_HUGETLB)
29 #endif
30 
31 static void check_bytes(char *addr)
32 {
33 	printf("First hex is %x\n", *((unsigned int *)addr));
34 }
35 
36 static void write_bytes(char *addr, size_t length)
37 {
38 	unsigned long i;
39 
40 	for (i = 0; i < length; i++)
41 		*(addr + i) = (char)i;
42 }
43 
44 static int read_bytes(char *addr, size_t length)
45 {
46 	unsigned long i;
47 
48 	check_bytes(addr);
49 	for (i = 0; i < length; i++)
50 		if (*(addr + i) != (char)i) {
51 			printf("Mismatch at %lu\n", i);
52 			return 1;
53 		}
54 	return 0;
55 }
56 
57 int main(int argc, char **argv)
58 {
59 	void *addr;
60 	int ret;
61 	size_t length = LENGTH;
62 	int flags = FLAGS;
63 	int shift = 0;
64 
65 	if (argc > 1)
66 		length = atol(argv[1]) << 20;
67 	if (argc > 2) {
68 		shift = atoi(argv[2]);
69 		if (shift)
70 			flags |= (shift & MAP_HUGE_MASK) << MAP_HUGE_SHIFT;
71 	}
72 
73 	if (shift)
74 		printf("%u kB hugepages\n", 1 << (shift - 10));
75 	else
76 		printf("Default size hugepages\n");
77 	printf("Mapping %lu Mbytes\n", (unsigned long)length >> 20);
78 
79 	addr = mmap(ADDR, length, PROTECTION, flags, -1, 0);
80 	if (addr == MAP_FAILED) {
81 		perror("mmap");
82 		exit(1);
83 	}
84 
85 	printf("Returned address is %p\n", addr);
86 	check_bytes(addr);
87 	write_bytes(addr, length);
88 	ret = read_bytes(addr, length);
89 
90 	/* munmap() length of MAP_HUGETLB memory must be hugepage aligned */
91 	if (munmap(addr, length)) {
92 		perror("munmap");
93 		exit(1);
94 	}
95 
96 	return ret;
97 }
98