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 33 static void check_bytes(char *addr) 34 { 35 printf("First hex is %x\n", *((unsigned int *)addr)); 36 } 37 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 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 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 } 108 109 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