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/*
* Support for RAM backed by mmaped host memory.
*
* Copyright (c) 2015 Red Hat, Inc.
*
* Authors:
* Michael S. Tsirkin <mst@redhat.com>
*
* This work is licensed under the terms of the GNU GPL, version 2 or
* later. See the COPYING file in the top-level directory.
*/
#include "qemu/osdep.h"
#include "qemu/mmap-alloc.h"
#include "qemu/host-utils.h"
#define HUGETLBFS_MAGIC 0x958458f6
#ifdef CONFIG_LINUX
#include <sys/vfs.h>
#endif
size_t qemu_fd_getpagesize(int fd)
{
#ifdef CONFIG_LINUX
struct statfs fs;
int ret;
if (fd != -1) {
do {
ret = fstatfs(fd, &fs);
} while (ret != 0 && errno == EINTR);
if (ret == 0 && fs.f_type == HUGETLBFS_MAGIC) {
return fs.f_bsize;
}
}
#endif
return getpagesize();
}
void *qemu_ram_mmap(int fd, size_t size, size_t align, bool shared)
{
/*
* Note: this always allocates at least one extra page of virtual address
* space, even if size is already aligned.
*/
size_t total = size + align;
#if defined(__powerpc64__) && defined(__linux__)
/* On ppc64 mappings in the same segment (aka slice) must share the same
* page size. Since we will be re-allocating part of this segment
* from the supplied fd, we should make sure to use the same page size, to
* this end we mmap the supplied fd. In this case, set MAP_NORESERVE to
* avoid allocating backing store memory.
* We do this unless we are using the system page size, in which case
* anonymous memory is OK.
*/
int anonfd = fd == -1 || qemu_fd_getpagesize(fd) == getpagesize() ? -1 : fd;
int flags = anonfd == -1 ? MAP_ANONYMOUS : MAP_NORESERVE;
void *ptr = mmap(0, total, PROT_NONE, flags | MAP_PRIVATE, anonfd, 0);
#else
void *ptr = mmap(0, total, PROT_NONE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
#endif
size_t offset;
void *ptr1;
if (ptr == MAP_FAILED) {
return MAP_FAILED;
}
assert(is_power_of_2(align));
/* Always align to host page size */
assert(align >= getpagesize());
offset = QEMU_ALIGN_UP((uintptr_t)ptr, align) - (uintptr_t)ptr;
ptr1 = mmap(ptr + offset, size, PROT_READ | PROT_WRITE,
MAP_FIXED |
(fd == -1 ? MAP_ANONYMOUS : 0) |
(shared ? MAP_SHARED : MAP_PRIVATE),
fd, 0);
if (ptr1 == MAP_FAILED) {
munmap(ptr, total);
return MAP_FAILED;
}
if (offset > 0) {
munmap(ptr, offset);
}
/*
* Leave a single PROT_NONE page allocated after the RAM block, to serve as
* a guard page guarding against potential buffer overflows.
*/
total -= offset;
if (total > size + getpagesize()) {
munmap(ptr1 + size + getpagesize(), total - size - getpagesize());
}
return ptr1;
}
void qemu_ram_munmap(void *ptr, size_t size)
{
if (ptr) {
/* Unmap both the RAM block and the guard page */
munmap(ptr, size + getpagesize());
}
}
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