/* * Support for RAM backed by mmaped host memory. * * Copyright (c) 2015 Red Hat, Inc. * * Authors: * Michael S. Tsirkin <mst@redhat.com> * * This work is licensed under the terms of the GNU GPL, version 2 or * later. See the COPYING file in the top-level directory. */ #ifdef CONFIG_LINUX #include <linux/mman.h> #else /* !CONFIG_LINUX */ #define MAP_SYNC 0x0 #define MAP_SHARED_VALIDATE 0x0 #endif /* CONFIG_LINUX */ #include "qemu/osdep.h" #include "qemu/mmap-alloc.h" #include "qemu/host-utils.h" #define HUGETLBFS_MAGIC 0x958458f6 #ifdef CONFIG_LINUX #include <sys/vfs.h> #endif size_t qemu_fd_getpagesize(int fd) { #ifdef CONFIG_LINUX struct statfs fs; int ret; if (fd != -1) { do { ret = fstatfs(fd, &fs); } while (ret != 0 && errno == EINTR); if (ret == 0 && fs.f_type == HUGETLBFS_MAGIC) { return fs.f_bsize; } } #ifdef __sparc__ /* SPARC Linux needs greater alignment than the pagesize */ return QEMU_VMALLOC_ALIGN; #endif #endif return qemu_real_host_page_size; } size_t qemu_mempath_getpagesize(const char *mem_path) { #ifdef CONFIG_LINUX struct statfs fs; int ret; if (mem_path) { do { ret = statfs(mem_path, &fs); } while (ret != 0 && errno == EINTR); if (ret != 0) { fprintf(stderr, "Couldn't statfs() memory path: %s\n", strerror(errno)); exit(1); } if (fs.f_type == HUGETLBFS_MAGIC) { /* It's hugepage, return the huge page size */ return fs.f_bsize; } } #ifdef __sparc__ /* SPARC Linux needs greater alignment than the pagesize */ return QEMU_VMALLOC_ALIGN; #endif #endif return qemu_real_host_page_size; } void *qemu_ram_mmap(int fd, size_t size, size_t align, bool shared, bool is_pmem) { int flags; int map_sync_flags = 0; int guardfd; size_t offset; size_t pagesize; size_t total; void *guardptr; void *ptr; /* * Note: this always allocates at least one extra page of virtual address * space, even if size is already aligned. */ total = size + align; #if defined(__powerpc64__) && defined(__linux__) /* On ppc64 mappings in the same segment (aka slice) must share the same * page size. Since we will be re-allocating part of this segment * from the supplied fd, we should make sure to use the same page size, to * this end we mmap the supplied fd. In this case, set MAP_NORESERVE to * avoid allocating backing store memory. * We do this unless we are using the system page size, in which case * anonymous memory is OK. */ flags = MAP_PRIVATE; pagesize = qemu_fd_getpagesize(fd); if (fd == -1 || pagesize == qemu_real_host_page_size) { guardfd = -1; flags |= MAP_ANONYMOUS; } else { guardfd = fd; flags |= MAP_NORESERVE; } #else guardfd = -1; pagesize = qemu_real_host_page_size; flags = MAP_PRIVATE | MAP_ANONYMOUS; #endif guardptr = mmap(0, total, PROT_NONE, flags, guardfd, 0); if (guardptr == MAP_FAILED) { return MAP_FAILED; } assert(is_power_of_2(align)); /* Always align to host page size */ assert(align >= pagesize); flags = MAP_FIXED; flags |= fd == -1 ? MAP_ANONYMOUS : 0; flags |= shared ? MAP_SHARED : MAP_PRIVATE; if (shared && is_pmem) { map_sync_flags = MAP_SYNC | MAP_SHARED_VALIDATE; } offset = QEMU_ALIGN_UP((uintptr_t)guardptr, align) - (uintptr_t)guardptr; ptr = mmap(guardptr + offset, size, PROT_READ | PROT_WRITE, flags | map_sync_flags, fd, 0); if (ptr == MAP_FAILED && map_sync_flags) { if (errno == ENOTSUP) { char *proc_link, *file_name; int len; proc_link = g_strdup_printf("/proc/self/fd/%d", fd); file_name = g_malloc0(PATH_MAX); len = readlink(proc_link, file_name, PATH_MAX - 1); if (len < 0) { len = 0; } file_name[len] = '\0'; fprintf(stderr, "Warning: requesting persistence across crashes " "for backend file %s failed. Proceeding without " "persistence, data might become corrupted in case of host " "crash.\n", file_name); g_free(proc_link); g_free(file_name); } /* * if map failed with MAP_SHARED_VALIDATE | MAP_SYNC, * we will remove these flags to handle compatibility. */ ptr = mmap(guardptr + offset, size, PROT_READ | PROT_WRITE, flags, fd, 0); } if (ptr == MAP_FAILED) { munmap(guardptr, total); return MAP_FAILED; } if (offset > 0) { munmap(guardptr, offset); } /* * Leave a single PROT_NONE page allocated after the RAM block, to serve as * a guard page guarding against potential buffer overflows. */ total -= offset; if (total > size + pagesize) { munmap(ptr + size + pagesize, total - size - pagesize); } return ptr; } void qemu_ram_munmap(int fd, void *ptr, size_t size) { size_t pagesize; if (ptr) { /* Unmap both the RAM block and the guard page */ #if defined(__powerpc64__) && defined(__linux__) pagesize = qemu_fd_getpagesize(fd); #else pagesize = qemu_real_host_page_size; #endif munmap(ptr, size + pagesize); } }