2 * Support for RAM backed by mmaped host memory.
4 * Copyright (c) 2015 Red Hat, Inc.
7 * Michael S. Tsirkin <mst@redhat.com>
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.
13 #include "qemu/osdep.h"
14 #include "qemu/mmap-alloc.h"
15 #include "qemu/host-utils.h"
17 #define HUGETLBFS_MAGIC 0x958458f6
23 size_t qemu_fd_getpagesize(int fd)
31 ret = fstatfs(fd, &fs);
32 } while (ret != 0 && errno == EINTR);
34 if (ret == 0 && fs.f_type == HUGETLBFS_MAGIC) {
39 /* SPARC Linux needs greater alignment than the pagesize */
40 return QEMU_VMALLOC_ALIGN;
47 size_t qemu_mempath_getpagesize(const char *mem_path)
55 ret = statfs(mem_path, &fs);
56 } while (ret != 0 && errno == EINTR);
59 fprintf(stderr, "Couldn't statfs() memory path: %s\n",
64 if (fs.f_type == HUGETLBFS_MAGIC) {
65 /* It's hugepage, return the huge page size */
70 /* SPARC Linux needs greater alignment than the pagesize */
71 return QEMU_VMALLOC_ALIGN;
78 void *qemu_ram_mmap(int fd, size_t size, size_t align, bool shared)
81 * Note: this always allocates at least one extra page of virtual address
82 * space, even if size is already aligned.
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.
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);
98 void *ptr = mmap(0, total, PROT_NONE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
103 if (ptr == MAP_FAILED) {
107 assert(is_power_of_2(align));
108 /* Always align to host page size */
109 assert(align >= getpagesize());
111 offset = QEMU_ALIGN_UP((uintptr_t)ptr, align) - (uintptr_t)ptr;
112 ptr1 = mmap(ptr + offset, size, PROT_READ | PROT_WRITE,
114 (fd == -1 ? MAP_ANONYMOUS : 0) |
115 (shared ? MAP_SHARED : MAP_PRIVATE),
117 if (ptr1 == MAP_FAILED) {
127 * Leave a single PROT_NONE page allocated after the RAM block, to serve as
128 * a guard page guarding against potential buffer overflows.
131 if (total > size + getpagesize()) {
132 munmap(ptr1 + size + getpagesize(), total - size - getpagesize());
138 void qemu_ram_munmap(void *ptr, size_t size)
141 /* Unmap both the RAM block and the guard page */
142 munmap(ptr, size + getpagesize());