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 35 static void check_bytes(char *addr) 36 { 37 printf("First hex is %x\n", *((unsigned int *)addr)); 38 } 39 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 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 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 } 105 106 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