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 /* 81 * Note: this always allocates at least one extra page of virtual address 82 * space, even if size is already aligned. 83 */ 84 size_t total = size + align; 85 #if defined(__powerpc64__) && defined(__linux__) 86 /* On ppc64 mappings in the same segment (aka slice) must share the same 87 * page size. Since we will be re-allocating part of this segment 88 * from the supplied fd, we should make sure to use the same page size, to 89 * this end we mmap the supplied fd. In this case, set MAP_NORESERVE to 90 * avoid allocating backing store memory. 91 * We do this unless we are using the system page size, in which case 92 * anonymous memory is OK. 93 */ 94 int anonfd = fd == -1 || qemu_fd_getpagesize(fd) == getpagesize() ? -1 : fd; 95 int flags = anonfd == -1 ? MAP_ANONYMOUS : MAP_NORESERVE; 96 void *ptr = mmap(0, total, PROT_NONE, flags | MAP_PRIVATE, anonfd, 0); 97 #else 98 void *ptr = mmap(0, total, PROT_NONE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0); 99 #endif 100 size_t offset; 101 void *ptr1; 102 103 if (ptr == MAP_FAILED) { 104 return MAP_FAILED; 105 } 106 107 assert(is_power_of_2(align)); 108 /* Always align to host page size */ 109 assert(align >= getpagesize()); 110 111 offset = QEMU_ALIGN_UP((uintptr_t)ptr, align) - (uintptr_t)ptr; 112 ptr1 = mmap(ptr + offset, size, PROT_READ | PROT_WRITE, 113 MAP_FIXED | 114 (fd == -1 ? MAP_ANONYMOUS : 0) | 115 (shared ? MAP_SHARED : MAP_PRIVATE), 116 fd, 0); 117 if (ptr1 == MAP_FAILED) { 118 munmap(ptr, total); 119 return MAP_FAILED; 120 } 121 122 if (offset > 0) { 123 munmap(ptr, offset); 124 } 125 126 /* 127 * Leave a single PROT_NONE page allocated after the RAM block, to serve as 128 * a guard page guarding against potential buffer overflows. 129 */ 130 total -= offset; 131 if (total > size + getpagesize()) { 132 munmap(ptr1 + size + getpagesize(), total - size - getpagesize()); 133 } 134 135 return ptr1; 136 } 137 138 void qemu_ram_munmap(void *ptr, size_t size) 139 { 140 if (ptr) { 141 /* Unmap both the RAM block and the guard page */ 142 munmap(ptr, size + getpagesize()); 143 } 144 } 145