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    int flags;
  81    int guardfd;
  82    size_t offset;
  83    size_t pagesize;
  84    size_t total;
  85    void *guardptr;
  86    void *ptr;
  87
  88    /*
  89     * Note: this always allocates at least one extra page of virtual address
  90     * space, even if size is already aligned.
  91     */
  92    total = size + align;
  93
  94#if defined(__powerpc64__) && defined(__linux__)
  95    /* On ppc64 mappings in the same segment (aka slice) must share the same
  96     * page size. Since we will be re-allocating part of this segment
  97     * from the supplied fd, we should make sure to use the same page size, to
  98     * this end we mmap the supplied fd.  In this case, set MAP_NORESERVE to
  99     * avoid allocating backing store memory.
 100     * We do this unless we are using the system page size, in which case
 101     * anonymous memory is OK.
 102     */
 103    flags = MAP_PRIVATE;
 104    pagesize = qemu_fd_getpagesize(fd);
 105    if (fd == -1 || pagesize == getpagesize()) {
 106        guardfd = -1;
 107        flags |= MAP_ANONYMOUS;
 108    } else {
 109        guardfd = fd;
 110        flags |= MAP_NORESERVE;
 111    }
 112#else
 113    guardfd = -1;
 114    pagesize = getpagesize();
 115    flags = MAP_PRIVATE | MAP_ANONYMOUS;
 116#endif
 117
 118    guardptr = mmap(0, total, PROT_NONE, flags, guardfd, 0);
 119
 120    if (guardptr == MAP_FAILED) {
 121        return MAP_FAILED;
 122    }
 123
 124    assert(is_power_of_2(align));
 125    /* Always align to host page size */
 126    assert(align >= pagesize);
 127
 128    flags = MAP_FIXED;
 129    flags |= fd == -1 ? MAP_ANONYMOUS : 0;
 130    flags |= shared ? MAP_SHARED : MAP_PRIVATE;
 131    offset = QEMU_ALIGN_UP((uintptr_t)guardptr, align) - (uintptr_t)guardptr;
 132
 133    ptr = mmap(guardptr + offset, size, PROT_READ | PROT_WRITE, flags, fd, 0);
 134
 135    if (ptr == MAP_FAILED) {
 136        munmap(guardptr, total);
 137        return MAP_FAILED;
 138    }
 139
 140    if (offset > 0) {
 141        munmap(guardptr, offset);
 142    }
 143
 144    /*
 145     * Leave a single PROT_NONE page allocated after the RAM block, to serve as
 146     * a guard page guarding against potential buffer overflows.
 147     */
 148    total -= offset;
 149    if (total > size + pagesize) {
 150        munmap(ptr + size + pagesize, total - size - pagesize);
 151    }
 152
 153    return ptr;
 154}
 155
 156void qemu_ram_munmap(int fd, void *ptr, size_t size)
 157{
 158    size_t pagesize;
 159
 160    if (ptr) {
 161        /* Unmap both the RAM block and the guard page */
 162#if defined(__powerpc64__) && defined(__linux__)
 163        pagesize = qemu_fd_getpagesize(fd);
 164#else
 165        pagesize = getpagesize();
 166#endif
 167        munmap(ptr, size + pagesize);
 168    }
 169}
 170