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