213 lines
5.5 KiB
C
213 lines
5.5 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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#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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void *qemu_ram_mmap(int fd,
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size_t size,
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size_t align,
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bool shared,
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bool is_pmem)
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{
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int flags;
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int map_sync_flags = 0;
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int guardfd;
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size_t offset;
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size_t pagesize;
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size_t total;
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void *guardptr;
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void *ptr;
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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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#if defined(__powerpc64__) && defined(__linux__)
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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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flags = MAP_PRIVATE;
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pagesize = qemu_fd_getpagesize(fd);
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if (fd == -1 || pagesize == qemu_real_host_page_size) {
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guardfd = -1;
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flags |= MAP_ANONYMOUS;
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} else {
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guardfd = fd;
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flags |= MAP_NORESERVE;
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}
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#else
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guardfd = -1;
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pagesize = qemu_real_host_page_size;
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flags = MAP_PRIVATE | MAP_ANONYMOUS;
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#endif
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guardptr = mmap(0, total, PROT_NONE, flags, guardfd, 0);
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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 >= pagesize);
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flags = MAP_FIXED;
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flags |= fd == -1 ? MAP_ANONYMOUS : 0;
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flags |= shared ? MAP_SHARED : MAP_PRIVATE;
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if (shared && is_pmem) {
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map_sync_flags = MAP_SYNC | MAP_SHARED_VALIDATE;
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}
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offset = QEMU_ALIGN_UP((uintptr_t)guardptr, align) - (uintptr_t)guardptr;
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ptr = mmap(guardptr + offset, size, PROT_READ | PROT_WRITE,
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flags | map_sync_flags, fd, 0);
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if (ptr == MAP_FAILED && map_sync_flags) {
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if (errno == ENOTSUP) {
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char *proc_link, *file_name;
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int len;
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proc_link = g_strdup_printf("/proc/self/fd/%d", fd);
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file_name = g_malloc0(PATH_MAX);
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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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}
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/*
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* if map failed with MAP_SHARED_VALIDATE | MAP_SYNC,
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* we will remove these flags to handle compatibility.
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*/
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ptr = mmap(guardptr + offset, size, PROT_READ | PROT_WRITE,
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flags, fd, 0);
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}
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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 + pagesize) {
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munmap(ptr + size + pagesize, total - size - 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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size_t pagesize;
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if (ptr) {
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/* Unmap both the RAM block and the guard page */
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#if defined(__powerpc64__) && defined(__linux__)
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pagesize = qemu_fd_getpagesize(fd);
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#else
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pagesize = qemu_real_host_page_size;
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#endif
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munmap(ptr, size + pagesize);
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}
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}
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