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 #include "qemu/cutils.h" 24 #include "qemu/error-report.h" 25 26 #define HUGETLBFS_MAGIC 0x958458f6 27 28 #ifdef CONFIG_LINUX 29 #include <sys/vfs.h> 30 #endif 31 32 size_t qemu_fd_getpagesize(int fd) 33 { 34 #ifdef CONFIG_LINUX 35 struct statfs fs; 36 int ret; 37 38 if (fd != -1) { 39 do { 40 ret = fstatfs(fd, &fs); 41 } while (ret != 0 && errno == EINTR); 42 43 if (ret == 0 && fs.f_type == HUGETLBFS_MAGIC) { 44 return fs.f_bsize; 45 } 46 } 47 #ifdef __sparc__ 48 /* SPARC Linux needs greater alignment than the pagesize */ 49 return QEMU_VMALLOC_ALIGN; 50 #endif 51 #endif 52 53 return qemu_real_host_page_size(); 54 } 55 56 size_t qemu_mempath_getpagesize(const char *mem_path) 57 { 58 #ifdef CONFIG_LINUX 59 struct statfs fs; 60 int ret; 61 62 if (mem_path) { 63 do { 64 ret = statfs(mem_path, &fs); 65 } while (ret != 0 && errno == EINTR); 66 67 if (ret != 0) { 68 fprintf(stderr, "Couldn't statfs() memory path: %s\n", 69 strerror(errno)); 70 exit(1); 71 } 72 73 if (fs.f_type == HUGETLBFS_MAGIC) { 74 /* It's hugepage, return the huge page size */ 75 return fs.f_bsize; 76 } 77 } 78 #ifdef __sparc__ 79 /* SPARC Linux needs greater alignment than the pagesize */ 80 return QEMU_VMALLOC_ALIGN; 81 #endif 82 #endif 83 84 return qemu_real_host_page_size(); 85 } 86 87 #define OVERCOMMIT_MEMORY_PATH "/proc/sys/vm/overcommit_memory" 88 static bool map_noreserve_effective(int fd, uint32_t qemu_map_flags) 89 { 90 #if defined(__linux__) 91 const bool readonly = qemu_map_flags & QEMU_MAP_READONLY; 92 const bool shared = qemu_map_flags & QEMU_MAP_SHARED; 93 gchar *content = NULL; 94 const char *endptr; 95 unsigned int tmp; 96 97 /* 98 * hugeltb accounting is different than ordinary swap reservation: 99 * a) Hugetlb pages from the pool are reserved for both private and 100 * shared mappings. For shared mappings, all mappers have to specify 101 * MAP_NORESERVE. 102 * b) MAP_NORESERVE is not affected by /proc/sys/vm/overcommit_memory. 103 */ 104 if (qemu_fd_getpagesize(fd) != qemu_real_host_page_size()) { 105 return true; 106 } 107 108 /* 109 * Accountable mappings in the kernel that can be affected by MAP_NORESEVE 110 * are private writable mappings (see mm/mmap.c:accountable_mapping() in 111 * Linux). For all shared or readonly mappings, MAP_NORESERVE is always 112 * implicitly active -- no reservation; this includes shmem. The only 113 * exception is shared anonymous memory, it is accounted like private 114 * anonymous memory. 115 */ 116 if (readonly || (shared && fd >= 0)) { 117 return true; 118 } 119 120 /* 121 * MAP_NORESERVE is globally ignored for applicable !hugetlb mappings when 122 * memory overcommit is set to "never". Sparse memory regions aren't really 123 * possible in this system configuration. 124 * 125 * Bail out now instead of silently committing way more memory than 126 * currently desired by the user. 127 */ 128 if (g_file_get_contents(OVERCOMMIT_MEMORY_PATH, &content, NULL, NULL) && 129 !qemu_strtoui(content, &endptr, 0, &tmp) && 130 (!endptr || *endptr == '\n')) { 131 if (tmp == 2) { 132 error_report("Skipping reservation of swap space is not supported:" 133 " \"" OVERCOMMIT_MEMORY_PATH "\" is \"2\""); 134 return false; 135 } 136 return true; 137 } 138 /* this interface has been around since Linux 2.6 */ 139 error_report("Skipping reservation of swap space is not supported:" 140 " Could not read: \"" OVERCOMMIT_MEMORY_PATH "\""); 141 return false; 142 #endif 143 /* 144 * E.g., FreeBSD used to define MAP_NORESERVE, never implemented it, 145 * and removed it a while ago. 146 */ 147 error_report("Skipping reservation of swap space is not supported"); 148 return false; 149 } 150 151 /* 152 * Reserve a new memory region of the requested size to be used for mapping 153 * from the given fd (if any). 154 */ 155 static void *mmap_reserve(size_t size, int fd) 156 { 157 int flags = MAP_PRIVATE; 158 159 #if defined(__powerpc64__) && defined(__linux__) 160 /* 161 * On ppc64 mappings in the same segment (aka slice) must share the same 162 * page size. Since we will be re-allocating part of this segment 163 * from the supplied fd, we should make sure to use the same page size, to 164 * this end we mmap the supplied fd. In this case, set MAP_NORESERVE to 165 * avoid allocating backing store memory. 166 * We do this unless we are using the system page size, in which case 167 * anonymous memory is OK. 168 */ 169 if (fd == -1 || qemu_fd_getpagesize(fd) == qemu_real_host_page_size()) { 170 fd = -1; 171 flags |= MAP_ANONYMOUS; 172 } else { 173 flags |= MAP_NORESERVE; 174 } 175 #else 176 fd = -1; 177 flags |= MAP_ANONYMOUS; 178 #endif 179 180 return mmap(0, size, PROT_NONE, flags, fd, 0); 181 } 182 183 /* 184 * Activate memory in a reserved region from the given fd (if any), to make 185 * it accessible. 186 */ 187 static void *mmap_activate(void *ptr, size_t size, int fd, 188 uint32_t qemu_map_flags, off_t map_offset) 189 { 190 const bool noreserve = qemu_map_flags & QEMU_MAP_NORESERVE; 191 const bool readonly = qemu_map_flags & QEMU_MAP_READONLY; 192 const bool shared = qemu_map_flags & QEMU_MAP_SHARED; 193 const bool sync = qemu_map_flags & QEMU_MAP_SYNC; 194 const int prot = PROT_READ | (readonly ? 0 : PROT_WRITE); 195 int map_sync_flags = 0; 196 int flags = MAP_FIXED; 197 void *activated_ptr; 198 199 if (noreserve && !map_noreserve_effective(fd, qemu_map_flags)) { 200 return MAP_FAILED; 201 } 202 203 flags |= fd == -1 ? MAP_ANONYMOUS : 0; 204 flags |= shared ? MAP_SHARED : MAP_PRIVATE; 205 flags |= noreserve ? MAP_NORESERVE : 0; 206 if (shared && sync) { 207 map_sync_flags = MAP_SYNC | MAP_SHARED_VALIDATE; 208 } 209 210 activated_ptr = mmap(ptr, size, prot, flags | map_sync_flags, fd, 211 map_offset); 212 if (activated_ptr == MAP_FAILED && map_sync_flags) { 213 if (errno == ENOTSUP) { 214 char *proc_link = g_strdup_printf("/proc/self/fd/%d", fd); 215 char *file_name = g_malloc0(PATH_MAX); 216 int len = readlink(proc_link, file_name, PATH_MAX - 1); 217 218 if (len < 0) { 219 len = 0; 220 } 221 file_name[len] = '\0'; 222 fprintf(stderr, "Warning: requesting persistence across crashes " 223 "for backend file %s failed. Proceeding without " 224 "persistence, data might become corrupted in case of host " 225 "crash.\n", file_name); 226 g_free(proc_link); 227 g_free(file_name); 228 warn_report("Using non DAX backing file with 'pmem=on' option" 229 " is deprecated"); 230 } 231 /* 232 * If mmap failed with MAP_SHARED_VALIDATE | MAP_SYNC, we will try 233 * again without these flags to handle backwards compatibility. 234 */ 235 activated_ptr = mmap(ptr, size, prot, flags, fd, map_offset); 236 } 237 return activated_ptr; 238 } 239 240 static inline size_t mmap_guard_pagesize(int fd) 241 { 242 #if defined(__powerpc64__) && defined(__linux__) 243 /* Mappings in the same segment must share the same page size */ 244 return qemu_fd_getpagesize(fd); 245 #else 246 return qemu_real_host_page_size(); 247 #endif 248 } 249 250 void *qemu_ram_mmap(int fd, 251 size_t size, 252 size_t align, 253 uint32_t qemu_map_flags, 254 off_t map_offset) 255 { 256 const size_t guard_pagesize = mmap_guard_pagesize(fd); 257 size_t offset, total; 258 void *ptr, *guardptr; 259 260 /* 261 * Note: this always allocates at least one extra page of virtual address 262 * space, even if size is already aligned. 263 */ 264 total = size + align; 265 266 guardptr = mmap_reserve(total, fd); 267 if (guardptr == MAP_FAILED) { 268 return MAP_FAILED; 269 } 270 271 assert(is_power_of_2(align)); 272 /* Always align to host page size */ 273 assert(align >= guard_pagesize); 274 275 offset = QEMU_ALIGN_UP((uintptr_t)guardptr, align) - (uintptr_t)guardptr; 276 277 ptr = mmap_activate(guardptr + offset, size, fd, qemu_map_flags, 278 map_offset); 279 if (ptr == MAP_FAILED) { 280 munmap(guardptr, total); 281 return MAP_FAILED; 282 } 283 284 if (offset > 0) { 285 munmap(guardptr, offset); 286 } 287 288 /* 289 * Leave a single PROT_NONE page allocated after the RAM block, to serve as 290 * a guard page guarding against potential buffer overflows. 291 */ 292 total -= offset; 293 if (total > size + guard_pagesize) { 294 munmap(ptr + size + guard_pagesize, total - size - guard_pagesize); 295 } 296 297 return ptr; 298 } 299 300 void qemu_ram_munmap(int fd, void *ptr, size_t size) 301 { 302 if (ptr) { 303 /* Unmap both the RAM block and the guard page */ 304 munmap(ptr, size + mmap_guard_pagesize(fd)); 305 } 306 } 307