/* * 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" #include "qemu/cutils.h" #include "qemu/error-report.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(); } #define OVERCOMMIT_MEMORY_PATH "/proc/sys/vm/overcommit_memory" static bool map_noreserve_effective(int fd, uint32_t qemu_map_flags) { #if defined(__linux__) const bool readonly = qemu_map_flags & QEMU_MAP_READONLY; const bool shared = qemu_map_flags & QEMU_MAP_SHARED; gchar *content = NULL; const char *endptr; unsigned int tmp; /* * hugeltb accounting is different than ordinary swap reservation: * a) Hugetlb pages from the pool are reserved for both private and * shared mappings. For shared mappings, all mappers have to specify * MAP_NORESERVE. * b) MAP_NORESERVE is not affected by /proc/sys/vm/overcommit_memory. */ if (qemu_fd_getpagesize(fd) != qemu_real_host_page_size()) { return true; } /* * Accountable mappings in the kernel that can be affected by MAP_NORESEVE * are private writable mappings (see mm/mmap.c:accountable_mapping() in * Linux). For all shared or readonly mappings, MAP_NORESERVE is always * implicitly active -- no reservation; this includes shmem. The only * exception is shared anonymous memory, it is accounted like private * anonymous memory. */ if (readonly || (shared && fd >= 0)) { return true; } /* * MAP_NORESERVE is globally ignored for applicable !hugetlb mappings when * memory overcommit is set to "never". Sparse memory regions aren't really * possible in this system configuration. * * Bail out now instead of silently committing way more memory than * currently desired by the user. */ if (g_file_get_contents(OVERCOMMIT_MEMORY_PATH, &content, NULL, NULL) && !qemu_strtoui(content, &endptr, 0, &tmp) && (!endptr || *endptr == '\n')) { if (tmp == 2) { error_report("Skipping reservation of swap space is not supported:" " \"" OVERCOMMIT_MEMORY_PATH "\" is \"2\""); return false; } return true; } /* this interface has been around since Linux 2.6 */ error_report("Skipping reservation of swap space is not supported:" " Could not read: \"" OVERCOMMIT_MEMORY_PATH "\""); return false; #endif /* * E.g., FreeBSD used to define MAP_NORESERVE, never implemented it, * and removed it a while ago. */ error_report("Skipping reservation of swap space is not supported"); return false; } /* * Reserve a new memory region of the requested size to be used for mapping * from the given fd (if any). */ static void *mmap_reserve(size_t size, int fd) { int flags = MAP_PRIVATE; #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. */ if (fd == -1 || qemu_fd_getpagesize(fd) == qemu_real_host_page_size()) { fd = -1; flags |= MAP_ANONYMOUS; } else { flags |= MAP_NORESERVE; } #else fd = -1; flags |= MAP_ANONYMOUS; #endif return mmap(0, size, PROT_NONE, flags, fd, 0); } /* * Activate memory in a reserved region from the given fd (if any), to make * it accessible. */ static void *mmap_activate(void *ptr, size_t size, int fd, uint32_t qemu_map_flags, off_t map_offset) { const bool noreserve = qemu_map_flags & QEMU_MAP_NORESERVE; const bool readonly = qemu_map_flags & QEMU_MAP_READONLY; const bool shared = qemu_map_flags & QEMU_MAP_SHARED; const bool sync = qemu_map_flags & QEMU_MAP_SYNC; const int prot = PROT_READ | (readonly ? 0 : PROT_WRITE); int map_sync_flags = 0; int flags = MAP_FIXED; void *activated_ptr; if (noreserve && !map_noreserve_effective(fd, qemu_map_flags)) { return MAP_FAILED; } flags |= fd == -1 ? MAP_ANONYMOUS : 0; flags |= shared ? MAP_SHARED : MAP_PRIVATE; flags |= noreserve ? MAP_NORESERVE : 0; if (shared && sync) { map_sync_flags = MAP_SYNC | MAP_SHARED_VALIDATE; } activated_ptr = mmap(ptr, size, prot, flags | map_sync_flags, fd, map_offset); if (activated_ptr == MAP_FAILED && map_sync_flags) { if (errno == ENOTSUP) { char *proc_link = g_strdup_printf("/proc/self/fd/%d", fd); char *file_name = g_malloc0(PATH_MAX); int 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); warn_report("Using non DAX backing file with 'pmem=on' option" " is deprecated"); } /* * If mmap failed with MAP_SHARED_VALIDATE | MAP_SYNC, we will try * again without these flags to handle backwards compatibility. */ activated_ptr = mmap(ptr, size, prot, flags, fd, map_offset); } return activated_ptr; } static inline size_t mmap_guard_pagesize(int fd) { #if defined(__powerpc64__) && defined(__linux__) /* Mappings in the same segment must share the same page size */ return qemu_fd_getpagesize(fd); #else return qemu_real_host_page_size(); #endif } void *qemu_ram_mmap(int fd, size_t size, size_t align, uint32_t qemu_map_flags, off_t map_offset) { const size_t guard_pagesize = mmap_guard_pagesize(fd); size_t offset, total; void *ptr, *guardptr; /* * Note: this always allocates at least one extra page of virtual address * space, even if size is already aligned. */ total = size + align; guardptr = mmap_reserve(total, fd); if (guardptr == MAP_FAILED) { return MAP_FAILED; } assert(is_power_of_2(align)); /* Always align to host page size */ assert(align >= guard_pagesize); offset = QEMU_ALIGN_UP((uintptr_t)guardptr, align) - (uintptr_t)guardptr; ptr = mmap_activate(guardptr + offset, size, fd, qemu_map_flags, map_offset); 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 + guard_pagesize) { munmap(ptr + size + guard_pagesize, total - size - guard_pagesize); } return ptr; } void qemu_ram_munmap(int fd, void *ptr, size_t size) { if (ptr) { /* Unmap both the RAM block and the guard page */ munmap(ptr, size + mmap_guard_pagesize(fd)); } }