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 #include "qemu/osdep.h" 14 #include "qemu/mmap-alloc.h" 15 #include "qemu/host-utils.h" 16 17 #define HUGETLBFS_MAGIC 0x958458f6 18 19 #ifdef CONFIG_LINUX 20 #include <sys/vfs.h> 21 #endif 22 23 size_t qemu_fd_getpagesize(int fd) 24 { 25 #ifdef CONFIG_LINUX 26 struct statfs fs; 27 int ret; 28 29 if (fd != -1) { 30 do { 31 ret = fstatfs(fd, &fs); 32 } while (ret != 0 && errno == EINTR); 33 34 if (ret == 0 && fs.f_type == HUGETLBFS_MAGIC) { 35 return fs.f_bsize; 36 } 37 } 38 #ifdef __sparc__ 39 /* SPARC Linux needs greater alignment than the pagesize */ 40 return QEMU_VMALLOC_ALIGN; 41 #endif 42 #endif 43 44 return getpagesize(); 45 } 46 47 size_t qemu_mempath_getpagesize(const char *mem_path) 48 { 49 #ifdef CONFIG_LINUX 50 struct statfs fs; 51 int ret; 52 53 if (mem_path) { 54 do { 55 ret = statfs(mem_path, &fs); 56 } while (ret != 0 && errno == EINTR); 57 58 if (ret != 0) { 59 fprintf(stderr, "Couldn't statfs() memory path: %s\n", 60 strerror(errno)); 61 exit(1); 62 } 63 64 if (fs.f_type == HUGETLBFS_MAGIC) { 65 /* It's hugepage, return the huge page size */ 66 return fs.f_bsize; 67 } 68 } 69 #ifdef __sparc__ 70 /* SPARC Linux needs greater alignment than the pagesize */ 71 return QEMU_VMALLOC_ALIGN; 72 #endif 73 #endif 74 75 return getpagesize(); 76 } 77 78 void *qemu_ram_mmap(int fd, size_t size, size_t align, bool shared) 79 { 80 int flags; 81 int guardfd; 82 size_t offset; 83 size_t pagesize; 84 size_t total; 85 void *guardptr; 86 void *ptr; 87 88 /* 89 * Note: this always allocates at least one extra page of virtual address 90 * space, even if size is already aligned. 91 */ 92 total = size + align; 93 94 #if defined(__powerpc64__) && defined(__linux__) 95 /* On ppc64 mappings in the same segment (aka slice) must share the same 96 * page size. Since we will be re-allocating part of this segment 97 * from the supplied fd, we should make sure to use the same page size, to 98 * this end we mmap the supplied fd. In this case, set MAP_NORESERVE to 99 * avoid allocating backing store memory. 100 * We do this unless we are using the system page size, in which case 101 * anonymous memory is OK. 102 */ 103 flags = MAP_PRIVATE; 104 pagesize = qemu_fd_getpagesize(fd); 105 if (fd == -1 || pagesize == getpagesize()) { 106 guardfd = -1; 107 flags |= MAP_ANONYMOUS; 108 } else { 109 guardfd = fd; 110 flags |= MAP_NORESERVE; 111 } 112 #else 113 guardfd = -1; 114 pagesize = getpagesize(); 115 flags = MAP_PRIVATE | MAP_ANONYMOUS; 116 #endif 117 118 guardptr = mmap(0, total, PROT_NONE, flags, guardfd, 0); 119 120 if (guardptr == MAP_FAILED) { 121 return MAP_FAILED; 122 } 123 124 assert(is_power_of_2(align)); 125 /* Always align to host page size */ 126 assert(align >= pagesize); 127 128 flags = MAP_FIXED; 129 flags |= fd == -1 ? MAP_ANONYMOUS : 0; 130 flags |= shared ? MAP_SHARED : MAP_PRIVATE; 131 offset = QEMU_ALIGN_UP((uintptr_t)guardptr, align) - (uintptr_t)guardptr; 132 133 ptr = mmap(guardptr + offset, size, PROT_READ | PROT_WRITE, flags, fd, 0); 134 135 if (ptr == MAP_FAILED) { 136 munmap(guardptr, total); 137 return MAP_FAILED; 138 } 139 140 if (offset > 0) { 141 munmap(guardptr, offset); 142 } 143 144 /* 145 * Leave a single PROT_NONE page allocated after the RAM block, to serve as 146 * a guard page guarding against potential buffer overflows. 147 */ 148 total -= offset; 149 if (total > size + pagesize) { 150 munmap(ptr + size + pagesize, total - size - pagesize); 151 } 152 153 return ptr; 154 } 155 156 void qemu_ram_munmap(int fd, void *ptr, size_t size) 157 { 158 size_t pagesize; 159 160 if (ptr) { 161 /* Unmap both the RAM block and the guard page */ 162 #if defined(__powerpc64__) && defined(__linux__) 163 pagesize = qemu_fd_getpagesize(fd); 164 #else 165 pagesize = getpagesize(); 166 #endif 167 munmap(ptr, size + pagesize); 168 } 169 } 170