306 lines
9.1 KiB
C
306 lines
9.1 KiB
C
/*
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* Support for RAM backed by mmaped host memory.
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*
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* Copyright (c) 2015 Red Hat, Inc.
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*
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* Authors:
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* Michael S. Tsirkin <mst@redhat.com>
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*
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* This work is licensed under the terms of the GNU GPL, version 2 or
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* later. See the COPYING file in the top-level directory.
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*/
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#ifdef CONFIG_LINUX
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#include <linux/mman.h>
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#else /* !CONFIG_LINUX */
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#define MAP_SYNC 0x0
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#define MAP_SHARED_VALIDATE 0x0
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#endif /* CONFIG_LINUX */
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#include "qemu/osdep.h"
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#include "qemu/mmap-alloc.h"
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#include "qemu/host-utils.h"
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#include "qemu/cutils.h"
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#include "qemu/error-report.h"
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#define HUGETLBFS_MAGIC 0x958458f6
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#ifdef CONFIG_LINUX
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#include <sys/vfs.h>
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#endif
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size_t qemu_fd_getpagesize(int fd)
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{
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#ifdef CONFIG_LINUX
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struct statfs fs;
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int ret;
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if (fd != -1) {
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do {
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ret = fstatfs(fd, &fs);
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} while (ret != 0 && errno == EINTR);
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if (ret == 0 && fs.f_type == HUGETLBFS_MAGIC) {
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return fs.f_bsize;
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}
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}
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#ifdef __sparc__
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/* SPARC Linux needs greater alignment than the pagesize */
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return QEMU_VMALLOC_ALIGN;
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#endif
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#endif
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return qemu_real_host_page_size();
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}
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size_t qemu_mempath_getpagesize(const char *mem_path)
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{
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#ifdef CONFIG_LINUX
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struct statfs fs;
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int ret;
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if (mem_path) {
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do {
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ret = statfs(mem_path, &fs);
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} while (ret != 0 && errno == EINTR);
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if (ret != 0) {
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fprintf(stderr, "Couldn't statfs() memory path: %s\n",
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strerror(errno));
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exit(1);
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}
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if (fs.f_type == HUGETLBFS_MAGIC) {
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/* It's hugepage, return the huge page size */
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return fs.f_bsize;
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}
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}
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#ifdef __sparc__
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/* SPARC Linux needs greater alignment than the pagesize */
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return QEMU_VMALLOC_ALIGN;
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#endif
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#endif
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return qemu_real_host_page_size();
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}
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#define OVERCOMMIT_MEMORY_PATH "/proc/sys/vm/overcommit_memory"
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static bool map_noreserve_effective(int fd, uint32_t qemu_map_flags)
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{
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#if defined(__linux__)
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const bool readonly = qemu_map_flags & QEMU_MAP_READONLY;
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const bool shared = qemu_map_flags & QEMU_MAP_SHARED;
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gchar *content = NULL;
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const char *endptr;
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unsigned int tmp;
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/*
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* hugeltb accounting is different than ordinary swap reservation:
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* a) Hugetlb pages from the pool are reserved for both private and
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* shared mappings. For shared mappings, all mappers have to specify
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* MAP_NORESERVE.
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* b) MAP_NORESERVE is not affected by /proc/sys/vm/overcommit_memory.
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*/
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if (qemu_fd_getpagesize(fd) != qemu_real_host_page_size()) {
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return true;
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}
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/*
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* Accountable mappings in the kernel that can be affected by MAP_NORESEVE
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* are private writable mappings (see mm/mmap.c:accountable_mapping() in
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* Linux). For all shared or readonly mappings, MAP_NORESERVE is always
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* implicitly active -- no reservation; this includes shmem. The only
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* exception is shared anonymous memory, it is accounted like private
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* anonymous memory.
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*/
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if (readonly || (shared && fd >= 0)) {
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return true;
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}
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/*
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* MAP_NORESERVE is globally ignored for applicable !hugetlb mappings when
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* memory overcommit is set to "never". Sparse memory regions aren't really
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* possible in this system configuration.
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*
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* Bail out now instead of silently committing way more memory than
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* currently desired by the user.
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*/
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if (g_file_get_contents(OVERCOMMIT_MEMORY_PATH, &content, NULL, NULL) &&
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!qemu_strtoui(content, &endptr, 0, &tmp) &&
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(!endptr || *endptr == '\n')) {
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if (tmp == 2) {
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error_report("Skipping reservation of swap space is not supported:"
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" \"" OVERCOMMIT_MEMORY_PATH "\" is \"2\"");
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return false;
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}
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return true;
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}
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/* this interface has been around since Linux 2.6 */
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error_report("Skipping reservation of swap space is not supported:"
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" Could not read: \"" OVERCOMMIT_MEMORY_PATH "\"");
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return false;
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#endif
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/*
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* E.g., FreeBSD used to define MAP_NORESERVE, never implemented it,
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* and removed it a while ago.
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*/
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error_report("Skipping reservation of swap space is not supported");
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return false;
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}
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/*
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* Reserve a new memory region of the requested size to be used for mapping
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* from the given fd (if any).
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*/
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static void *mmap_reserve(size_t size, int fd)
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{
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int flags = MAP_PRIVATE;
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#if defined(__powerpc64__) && defined(__linux__)
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/*
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* On ppc64 mappings in the same segment (aka slice) must share the same
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* page size. Since we will be re-allocating part of this segment
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* from the supplied fd, we should make sure to use the same page size, to
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* this end we mmap the supplied fd. In this case, set MAP_NORESERVE to
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* avoid allocating backing store memory.
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* We do this unless we are using the system page size, in which case
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* anonymous memory is OK.
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*/
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if (fd == -1 || qemu_fd_getpagesize(fd) == qemu_real_host_page_size()) {
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fd = -1;
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flags |= MAP_ANONYMOUS;
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} else {
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flags |= MAP_NORESERVE;
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}
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#else
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fd = -1;
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flags |= MAP_ANONYMOUS;
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#endif
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return mmap(0, size, PROT_NONE, flags, fd, 0);
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}
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/*
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* Activate memory in a reserved region from the given fd (if any), to make
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* it accessible.
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*/
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static void *mmap_activate(void *ptr, size_t size, int fd,
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uint32_t qemu_map_flags, off_t map_offset)
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{
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const bool noreserve = qemu_map_flags & QEMU_MAP_NORESERVE;
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const bool readonly = qemu_map_flags & QEMU_MAP_READONLY;
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const bool shared = qemu_map_flags & QEMU_MAP_SHARED;
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const bool sync = qemu_map_flags & QEMU_MAP_SYNC;
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const int prot = PROT_READ | (readonly ? 0 : PROT_WRITE);
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int map_sync_flags = 0;
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int flags = MAP_FIXED;
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void *activated_ptr;
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if (noreserve && !map_noreserve_effective(fd, qemu_map_flags)) {
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return MAP_FAILED;
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}
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flags |= fd == -1 ? MAP_ANONYMOUS : 0;
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flags |= shared ? MAP_SHARED : MAP_PRIVATE;
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flags |= noreserve ? MAP_NORESERVE : 0;
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if (shared && sync) {
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map_sync_flags = MAP_SYNC | MAP_SHARED_VALIDATE;
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}
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activated_ptr = mmap(ptr, size, prot, flags | map_sync_flags, fd,
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map_offset);
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if (activated_ptr == MAP_FAILED && map_sync_flags) {
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if (errno == ENOTSUP) {
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char *proc_link = g_strdup_printf("/proc/self/fd/%d", fd);
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char *file_name = g_malloc0(PATH_MAX);
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int len = readlink(proc_link, file_name, PATH_MAX - 1);
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if (len < 0) {
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len = 0;
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}
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file_name[len] = '\0';
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fprintf(stderr, "Warning: requesting persistence across crashes "
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"for backend file %s failed. Proceeding without "
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"persistence, data might become corrupted in case of host "
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"crash.\n", file_name);
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g_free(proc_link);
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g_free(file_name);
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warn_report("Using non DAX backing file with 'pmem=on' option"
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" is deprecated");
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}
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/*
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* If mmap failed with MAP_SHARED_VALIDATE | MAP_SYNC, we will try
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* again without these flags to handle backwards compatibility.
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*/
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activated_ptr = mmap(ptr, size, prot, flags, fd, map_offset);
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}
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return activated_ptr;
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}
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static inline size_t mmap_guard_pagesize(int fd)
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{
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#if defined(__powerpc64__) && defined(__linux__)
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/* Mappings in the same segment must share the same page size */
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return qemu_fd_getpagesize(fd);
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#else
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return qemu_real_host_page_size();
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#endif
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}
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void *qemu_ram_mmap(int fd,
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size_t size,
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size_t align,
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uint32_t qemu_map_flags,
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off_t map_offset)
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{
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const size_t guard_pagesize = mmap_guard_pagesize(fd);
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size_t offset, total;
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void *ptr, *guardptr;
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/*
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* Note: this always allocates at least one extra page of virtual address
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* space, even if size is already aligned.
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*/
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total = size + align;
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guardptr = mmap_reserve(total, fd);
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if (guardptr == MAP_FAILED) {
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return MAP_FAILED;
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}
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assert(is_power_of_2(align));
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/* Always align to host page size */
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assert(align >= guard_pagesize);
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offset = QEMU_ALIGN_UP((uintptr_t)guardptr, align) - (uintptr_t)guardptr;
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ptr = mmap_activate(guardptr + offset, size, fd, qemu_map_flags,
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map_offset);
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if (ptr == MAP_FAILED) {
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munmap(guardptr, total);
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return MAP_FAILED;
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}
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if (offset > 0) {
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munmap(guardptr, offset);
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}
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/*
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* Leave a single PROT_NONE page allocated after the RAM block, to serve as
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* a guard page guarding against potential buffer overflows.
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*/
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total -= offset;
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if (total > size + guard_pagesize) {
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munmap(ptr + size + guard_pagesize, total - size - guard_pagesize);
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}
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return ptr;
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}
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void qemu_ram_munmap(int fd, void *ptr, size_t size)
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{
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if (ptr) {
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/* Unmap both the RAM block and the guard page */
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munmap(ptr, size + mmap_guard_pagesize(fd));
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}
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}
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