1 /* 2 * Support for RAM backed by mmaped host memory. 3 * 4 * Copyright (c) 2015 Red Hat, Inc. 5 * 6 * Authors: 7 * Michael S. Tsirkin <mst@redhat.com> 8 * 9 * This work is licensed under the terms of the GNU GPL, version 2 or 10 * later. See the COPYING file in the top-level directory. 11 */ 12 13 #ifdef CONFIG_LINUX 14 #include <linux/mman.h> 15 #else /* !CONFIG_LINUX */ 16 #define MAP_SYNC 0x0 17 #define MAP_SHARED_VALIDATE 0x0 18 #endif /* CONFIG_LINUX */ 19 20 #include "qemu/osdep.h" 21 #include "qemu/mmap-alloc.h" 22 #include "qemu/host-utils.h" 23 24 #define HUGETLBFS_MAGIC 0x958458f6 25 26 #ifdef CONFIG_LINUX 27 #include <sys/vfs.h> 28 #endif 29 30 size_t qemu_fd_getpagesize(int fd) 31 { 32 #ifdef CONFIG_LINUX 33 struct statfs fs; 34 int ret; 35 36 if (fd != -1) { 37 do { 38 ret = fstatfs(fd, &fs); 39 } while (ret != 0 && errno == EINTR); 40 41 if (ret == 0 && fs.f_type == HUGETLBFS_MAGIC) { 42 return fs.f_bsize; 43 } 44 } 45 #ifdef __sparc__ 46 /* SPARC Linux needs greater alignment than the pagesize */ 47 return QEMU_VMALLOC_ALIGN; 48 #endif 49 #endif 50 51 return qemu_real_host_page_size; 52 } 53 54 size_t qemu_mempath_getpagesize(const char *mem_path) 55 { 56 #ifdef CONFIG_LINUX 57 struct statfs fs; 58 int ret; 59 60 if (mem_path) { 61 do { 62 ret = statfs(mem_path, &fs); 63 } while (ret != 0 && errno == EINTR); 64 65 if (ret != 0) { 66 fprintf(stderr, "Couldn't statfs() memory path: %s\n", 67 strerror(errno)); 68 exit(1); 69 } 70 71 if (fs.f_type == HUGETLBFS_MAGIC) { 72 /* It's hugepage, return the huge page size */ 73 return fs.f_bsize; 74 } 75 } 76 #ifdef __sparc__ 77 /* SPARC Linux needs greater alignment than the pagesize */ 78 return QEMU_VMALLOC_ALIGN; 79 #endif 80 #endif 81 82 return qemu_real_host_page_size; 83 } 84 85 void *qemu_ram_mmap(int fd, 86 size_t size, 87 size_t align, 88 bool readonly, 89 bool shared, 90 bool is_pmem, 91 off_t map_offset) 92 { 93 int prot; 94 int flags; 95 int map_sync_flags = 0; 96 int guardfd; 97 size_t offset; 98 size_t pagesize; 99 size_t total; 100 void *guardptr; 101 void *ptr; 102 103 /* 104 * Note: this always allocates at least one extra page of virtual address 105 * space, even if size is already aligned. 106 */ 107 total = size + align; 108 109 #if defined(__powerpc64__) && defined(__linux__) 110 /* On ppc64 mappings in the same segment (aka slice) must share the same 111 * page size. Since we will be re-allocating part of this segment 112 * from the supplied fd, we should make sure to use the same page size, to 113 * this end we mmap the supplied fd. In this case, set MAP_NORESERVE to 114 * avoid allocating backing store memory. 115 * We do this unless we are using the system page size, in which case 116 * anonymous memory is OK. 117 */ 118 flags = MAP_PRIVATE; 119 pagesize = qemu_fd_getpagesize(fd); 120 if (fd == -1 || pagesize == qemu_real_host_page_size) { 121 guardfd = -1; 122 flags |= MAP_ANONYMOUS; 123 } else { 124 guardfd = fd; 125 flags |= MAP_NORESERVE; 126 } 127 #else 128 guardfd = -1; 129 pagesize = qemu_real_host_page_size; 130 flags = MAP_PRIVATE | MAP_ANONYMOUS; 131 #endif 132 133 guardptr = mmap(0, total, PROT_NONE, flags, guardfd, 0); 134 135 if (guardptr == MAP_FAILED) { 136 return MAP_FAILED; 137 } 138 139 assert(is_power_of_2(align)); 140 /* Always align to host page size */ 141 assert(align >= pagesize); 142 143 flags = MAP_FIXED; 144 flags |= fd == -1 ? MAP_ANONYMOUS : 0; 145 flags |= shared ? MAP_SHARED : MAP_PRIVATE; 146 if (shared && is_pmem) { 147 map_sync_flags = MAP_SYNC | MAP_SHARED_VALIDATE; 148 } 149 150 offset = QEMU_ALIGN_UP((uintptr_t)guardptr, align) - (uintptr_t)guardptr; 151 152 prot = PROT_READ | (readonly ? 0 : PROT_WRITE); 153 154 ptr = mmap(guardptr + offset, size, prot, 155 flags | map_sync_flags, fd, map_offset); 156 157 if (ptr == MAP_FAILED && map_sync_flags) { 158 if (errno == ENOTSUP) { 159 char *proc_link, *file_name; 160 int len; 161 proc_link = g_strdup_printf("/proc/self/fd/%d", fd); 162 file_name = g_malloc0(PATH_MAX); 163 len = readlink(proc_link, file_name, PATH_MAX - 1); 164 if (len < 0) { 165 len = 0; 166 } 167 file_name[len] = '\0'; 168 fprintf(stderr, "Warning: requesting persistence across crashes " 169 "for backend file %s failed. Proceeding without " 170 "persistence, data might become corrupted in case of host " 171 "crash.\n", file_name); 172 g_free(proc_link); 173 g_free(file_name); 174 } 175 /* 176 * if map failed with MAP_SHARED_VALIDATE | MAP_SYNC, 177 * we will remove these flags to handle compatibility. 178 */ 179 ptr = mmap(guardptr + offset, size, prot, flags, fd, map_offset); 180 } 181 182 if (ptr == MAP_FAILED) { 183 munmap(guardptr, total); 184 return MAP_FAILED; 185 } 186 187 if (offset > 0) { 188 munmap(guardptr, offset); 189 } 190 191 /* 192 * Leave a single PROT_NONE page allocated after the RAM block, to serve as 193 * a guard page guarding against potential buffer overflows. 194 */ 195 total -= offset; 196 if (total > size + pagesize) { 197 munmap(ptr + size + pagesize, total - size - pagesize); 198 } 199 200 return ptr; 201 } 202 203 void qemu_ram_munmap(int fd, void *ptr, size_t size) 204 { 205 size_t pagesize; 206 207 if (ptr) { 208 /* Unmap both the RAM block and the guard page */ 209 #if defined(__powerpc64__) && defined(__linux__) 210 pagesize = qemu_fd_getpagesize(fd); 211 #else 212 pagesize = qemu_real_host_page_size; 213 #endif 214 munmap(ptr, size + pagesize); 215 } 216 } 217