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 shared, 89 bool is_pmem) 90 { 91 int flags; 92 int map_sync_flags = 0; 93 int guardfd; 94 size_t offset; 95 size_t pagesize; 96 size_t total; 97 void *guardptr; 98 void *ptr; 99 100 /* 101 * Note: this always allocates at least one extra page of virtual address 102 * space, even if size is already aligned. 103 */ 104 total = size + align; 105 106 #if defined(__powerpc64__) && defined(__linux__) 107 /* On ppc64 mappings in the same segment (aka slice) must share the same 108 * page size. Since we will be re-allocating part of this segment 109 * from the supplied fd, we should make sure to use the same page size, to 110 * this end we mmap the supplied fd. In this case, set MAP_NORESERVE to 111 * avoid allocating backing store memory. 112 * We do this unless we are using the system page size, in which case 113 * anonymous memory is OK. 114 */ 115 flags = MAP_PRIVATE; 116 pagesize = qemu_fd_getpagesize(fd); 117 if (fd == -1 || pagesize == qemu_real_host_page_size) { 118 guardfd = -1; 119 flags |= MAP_ANONYMOUS; 120 } else { 121 guardfd = fd; 122 flags |= MAP_NORESERVE; 123 } 124 #else 125 guardfd = -1; 126 pagesize = qemu_real_host_page_size; 127 flags = MAP_PRIVATE | MAP_ANONYMOUS; 128 #endif 129 130 guardptr = mmap(0, total, PROT_NONE, flags, guardfd, 0); 131 132 if (guardptr == MAP_FAILED) { 133 return MAP_FAILED; 134 } 135 136 assert(is_power_of_2(align)); 137 /* Always align to host page size */ 138 assert(align >= pagesize); 139 140 flags = MAP_FIXED; 141 flags |= fd == -1 ? MAP_ANONYMOUS : 0; 142 flags |= shared ? MAP_SHARED : MAP_PRIVATE; 143 if (shared && is_pmem) { 144 map_sync_flags = MAP_SYNC | MAP_SHARED_VALIDATE; 145 } 146 147 offset = QEMU_ALIGN_UP((uintptr_t)guardptr, align) - (uintptr_t)guardptr; 148 149 ptr = mmap(guardptr + offset, size, PROT_READ | PROT_WRITE, 150 flags | map_sync_flags, fd, 0); 151 152 if (ptr == MAP_FAILED && map_sync_flags) { 153 if (errno == ENOTSUP) { 154 char *proc_link, *file_name; 155 int len; 156 proc_link = g_strdup_printf("/proc/self/fd/%d", fd); 157 file_name = g_malloc0(PATH_MAX); 158 len = readlink(proc_link, file_name, PATH_MAX - 1); 159 if (len < 0) { 160 len = 0; 161 } 162 file_name[len] = '\0'; 163 fprintf(stderr, "Warning: requesting persistence across crashes " 164 "for backend file %s failed. Proceeding without " 165 "persistence, data might become corrupted in case of host " 166 "crash.\n", file_name); 167 g_free(proc_link); 168 g_free(file_name); 169 } 170 /* 171 * if map failed with MAP_SHARED_VALIDATE | MAP_SYNC, 172 * we will remove these flags to handle compatibility. 173 */ 174 ptr = mmap(guardptr + offset, size, PROT_READ | PROT_WRITE, 175 flags, fd, 0); 176 } 177 178 if (ptr == MAP_FAILED) { 179 munmap(guardptr, total); 180 return MAP_FAILED; 181 } 182 183 if (offset > 0) { 184 munmap(guardptr, offset); 185 } 186 187 /* 188 * Leave a single PROT_NONE page allocated after the RAM block, to serve as 189 * a guard page guarding against potential buffer overflows. 190 */ 191 total -= offset; 192 if (total > size + pagesize) { 193 munmap(ptr + size + pagesize, total - size - pagesize); 194 } 195 196 return ptr; 197 } 198 199 void qemu_ram_munmap(int fd, void *ptr, size_t size) 200 { 201 size_t pagesize; 202 203 if (ptr) { 204 /* Unmap both the RAM block and the guard page */ 205 #if defined(__powerpc64__) && defined(__linux__) 206 pagesize = qemu_fd_getpagesize(fd); 207 #else 208 pagesize = qemu_real_host_page_size; 209 #endif 210 munmap(ptr, size + pagesize); 211 } 212 } 213