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#ifdef __sparc__
  39    /* SPARC Linux needs greater alignment than the pagesize */
  40    return QEMU_VMALLOC_ALIGN;
  41#endif
  42#endif
  43
  44    return getpagesize();
  45}
  46
  47size_t qemu_mempath_getpagesize(const char *mem_path)
  48{
  49#ifdef CONFIG_LINUX
  50    struct statfs fs;
  51    int ret;
  52
  53    if (mem_path) {
  54        do {
  55            ret = statfs(mem_path, &fs);
  56        } while (ret != 0 && errno == EINTR);
  57
  58        if (ret != 0) {
  59            fprintf(stderr, "Couldn't statfs() memory path: %s\n",
  60                    strerror(errno));
  61            exit(1);
  62        }
  63
  64        if (fs.f_type == HUGETLBFS_MAGIC) {
  65            /* It's hugepage, return the huge page size */
  66            return fs.f_bsize;
  67        }
  68    }
  69#ifdef __sparc__
  70    /* SPARC Linux needs greater alignment than the pagesize */
  71    return QEMU_VMALLOC_ALIGN;
  72#endif
  73#endif
  74
  75    return getpagesize();
  76}
  77
  78void *qemu_ram_mmap(int fd, size_t size, size_t align, bool shared)
  79{
  80    /*
  81     * Note: this always allocates at least one extra page of virtual address
  82     * space, even if size is already aligned.
  83     */
  84    size_t total = size + align;
  85#if defined(__powerpc64__) && defined(__linux__)
  86    /* On ppc64 mappings in the same segment (aka slice) must share the same
  87     * page size. Since we will be re-allocating part of this segment
  88     * from the supplied fd, we should make sure to use the same page size, to
  89     * this end we mmap the supplied fd.  In this case, set MAP_NORESERVE to
  90     * avoid allocating backing store memory.
  91     * We do this unless we are using the system page size, in which case
  92     * anonymous memory is OK.
  93     */
  94    int anonfd = fd == -1 || qemu_fd_getpagesize(fd) == getpagesize() ? -1 : fd;
  95    int flags = anonfd == -1 ? MAP_ANONYMOUS : MAP_NORESERVE;
  96    void *ptr = mmap(0, total, PROT_NONE, flags | MAP_PRIVATE, anonfd, 0);
  97#else
  98    void *ptr = mmap(0, total, PROT_NONE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
  99#endif
 100    size_t offset;
 101    void *ptr1;
 102
 103    if (ptr == MAP_FAILED) {
 104        return MAP_FAILED;
 105    }
 106
 107    assert(is_power_of_2(align));
 108    /* Always align to host page size */
 109    assert(align >= getpagesize());
 110
 111    offset = QEMU_ALIGN_UP((uintptr_t)ptr, align) - (uintptr_t)ptr;
 112    ptr1 = mmap(ptr + offset, size, PROT_READ | PROT_WRITE,
 113                MAP_FIXED |
 114                (fd == -1 ? MAP_ANONYMOUS : 0) |
 115                (shared ? MAP_SHARED : MAP_PRIVATE),
 116                fd, 0);
 117    if (ptr1 == MAP_FAILED) {
 118        munmap(ptr, total);
 119        return MAP_FAILED;
 120    }
 121
 122    if (offset > 0) {
 123        munmap(ptr, offset);
 124    }
 125
 126    /*
 127     * Leave a single PROT_NONE page allocated after the RAM block, to serve as
 128     * a guard page guarding against potential buffer overflows.
 129     */
 130    total -= offset;
 131    if (total > size + getpagesize()) {
 132        munmap(ptr1 + size + getpagesize(), total - size - getpagesize());
 133    }
 134
 135    return ptr1;
 136}
 137
 138void qemu_ram_munmap(void *ptr, size_t size)
 139{
 140    if (ptr) {
 141        /* Unmap both the RAM block and the guard page */
 142        munmap(ptr, size + getpagesize());
 143    }
 144}
 145