LXR qemu/util/mmap-alloc.c

   1/*
   2 * Support for RAM backed by mmaped host memory.
   3 *
   4 * Copyright (c) 2015 Red Hat, Inc.
   5 *
   6 * Authors:
   7 *  Michael S. Tsirkin <mst@redhat.com>
   8 *
   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.
  11 */
  12
  13#include "qemu/osdep.h"
  14#include "qemu/mmap-alloc.h"
  15#include "qemu/host-utils.h"
  16
  17#define HUGETLBFS_MAGIC       0x958458f6
  18
  19#ifdef CONFIG_LINUX
  20#include <sys/vfs.h>
  21#endif
  22
  23size_t qemu_fd_getpagesize(int fd)
  24{
  25#ifdef CONFIG_LINUX
  26    struct statfs fs;
  27    int ret;
  28
  29    if (fd != -1) {
  30        do {
  31            ret = fstatfs(fd, &fs);
  32        } while (ret != 0 && errno == EINTR);
  33
  34        if (ret == 0 && fs.f_type == HUGETLBFS_MAGIC) {
  35            return fs.f_bsize;
  36        }
  37    }
  38#endif
  39
  40    return getpagesize();
  41}
  42
  43size_t qemu_mempath_getpagesize(const char *mem_path)
  44{
  45#ifdef CONFIG_LINUX
  46    struct statfs fs;
  47    int ret;
  48
  49    do {
  50        ret = statfs(mem_path, &fs);
  51    } while (ret != 0 && errno == EINTR);
  52
  53    if (ret != 0) {
  54        fprintf(stderr, "Couldn't statfs() memory path: %s\n",
  55                strerror(errno));
  56        exit(1);
  57    }
  58
  59    if (fs.f_type == HUGETLBFS_MAGIC) {
  60        /* It's hugepage, return the huge page size */
  61        return fs.f_bsize;
  62    }
  63#endif
  64
  65    return getpagesize();
  66}
  67
  68void *qemu_ram_mmap(int fd, size_t size, size_t align, bool shared)
  69{
  70    /*
  71     * Note: this always allocates at least one extra page of virtual address
  72     * space, even if size is already aligned.
  73     */
  74    size_t total = size + align;
  75#if defined(__powerpc64__) && defined(__linux__)
  76    /* On ppc64 mappings in the same segment (aka slice) must share the same
  77     * page size. Since we will be re-allocating part of this segment
  78     * from the supplied fd, we should make sure to use the same page size, to
  79     * this end we mmap the supplied fd.  In this case, set MAP_NORESERVE to
  80     * avoid allocating backing store memory.
  81     * We do this unless we are using the system page size, in which case
  82     * anonymous memory is OK.
  83     */
  84    int anonfd = fd == -1 || qemu_fd_getpagesize(fd) == getpagesize() ? -1 : fd;
  85    int flags = anonfd == -1 ? MAP_ANONYMOUS : MAP_NORESERVE;
  86    void *ptr = mmap(0, total, PROT_NONE, flags | MAP_PRIVATE, anonfd, 0);
  87#else
  88    void *ptr = mmap(0, total, PROT_NONE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
  89#endif
  90    size_t offset;
  91    void *ptr1;
  92
  93    if (ptr == MAP_FAILED) {
  94        return MAP_FAILED;
  95    }
  96
  97    assert(is_power_of_2(align));
  98    /* Always align to host page size */
  99    assert(align >= getpagesize());
 100
 101    offset = QEMU_ALIGN_UP((uintptr_t)ptr, align) - (uintptr_t)ptr;
 102    ptr1 = mmap(ptr + offset, size, PROT_READ | PROT_WRITE,
 103                MAP_FIXED |
 104                (fd == -1 ? MAP_ANONYMOUS : 0) |
 105                (shared ? MAP_SHARED : MAP_PRIVATE),
 106                fd, 0);
 107    if (ptr1 == MAP_FAILED) {
 108        munmap(ptr, total);
 109        return MAP_FAILED;
 110    }
 111
 112    if (offset > 0) {
 113        munmap(ptr, offset);
 114    }
 115
 116    /*
 117     * Leave a single PROT_NONE page allocated after the RAM block, to serve as
 118     * a guard page guarding against potential buffer overflows.
 119     */
 120    total -= offset;
 121    if (total > size + getpagesize()) {
 122        munmap(ptr1 + size + getpagesize(), total - size - getpagesize());
 123    }
 124
 125    return ptr1;
 126}
 127
 128void qemu_ram_munmap(void *ptr, size_t size)
 129{
 130    if (ptr) {
 131        /* Unmap both the RAM block and the guard page */
 132        munmap(ptr, size + getpagesize());
 133    }
 134}
 135