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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.
*/
#ifdef CONFIG_LINUX
#include <linux/mman.h>
#else /* !CONFIG_LINUX */
#define MAP_SYNC 0x0
#define MAP_SHARED_VALIDATE 0x0
#endif /* CONFIG_LINUX */
#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;
}
}
#ifdef __sparc__
/* SPARC Linux needs greater alignment than the pagesize */
return QEMU_VMALLOC_ALIGN;
#endif
#endif
return qemu_real_host_page_size;
}
size_t qemu_mempath_getpagesize(const char *mem_path)
{
#ifdef CONFIG_LINUX
struct statfs fs;
int ret;
if (mem_path) {
do {
ret = statfs(mem_path, &fs);
} while (ret != 0 && errno == EINTR);
if (ret != 0) {
fprintf(stderr, "Couldn't statfs() memory path: %s\n",
strerror(errno));
exit(1);
}
if (fs.f_type == HUGETLBFS_MAGIC) {
/* It's hugepage, return the huge page size */
return fs.f_bsize;
}
}
#ifdef __sparc__
/* SPARC Linux needs greater alignment than the pagesize */
return QEMU_VMALLOC_ALIGN;
#endif
#endif
return qemu_real_host_page_size;
}
void *qemu_ram_mmap(int fd,
size_t size,
size_t align,
bool readonly,
bool shared,
bool is_pmem)
{
int prot;
int flags;
int map_sync_flags = 0;
int guardfd;
size_t offset;
size_t pagesize;
size_t total;
void *guardptr;
void *ptr;
/*
* Note: this always allocates at least one extra page of virtual address
* space, even if size is already aligned.
*/
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.
*/
flags = MAP_PRIVATE;
pagesize = qemu_fd_getpagesize(fd);
if (fd == -1 || pagesize == qemu_real_host_page_size) {
guardfd = -1;
flags |= MAP_ANONYMOUS;
} else {
guardfd = fd;
flags |= MAP_NORESERVE;
}
#else
guardfd = -1;
pagesize = qemu_real_host_page_size;
flags = MAP_PRIVATE | MAP_ANONYMOUS;
#endif
guardptr = mmap(0, total, PROT_NONE, flags, guardfd, 0);
if (guardptr == MAP_FAILED) {
return MAP_FAILED;
}
assert(is_power_of_2(align));
/* Always align to host page size */
assert(align >= pagesize);
flags = MAP_FIXED;
flags |= fd == -1 ? MAP_ANONYMOUS : 0;
flags |= shared ? MAP_SHARED : MAP_PRIVATE;
if (shared && is_pmem) {
map_sync_flags = MAP_SYNC | MAP_SHARED_VALIDATE;
}
offset = QEMU_ALIGN_UP((uintptr_t)guardptr, align) - (uintptr_t)guardptr;
prot = PROT_READ | (readonly ? 0 : PROT_WRITE);
ptr = mmap(guardptr + offset, size, prot, flags | map_sync_flags, fd, 0);
if (ptr == MAP_FAILED && map_sync_flags) {
if (errno == ENOTSUP) {
char *proc_link, *file_name;
int len;
proc_link = g_strdup_printf("/proc/self/fd/%d", fd);
file_name = g_malloc0(PATH_MAX);
len = readlink(proc_link, file_name, PATH_MAX - 1);
if (len < 0) {
len = 0;
}
file_name[len] = '\0';
fprintf(stderr, "Warning: requesting persistence across crashes "
"for backend file %s failed. Proceeding without "
"persistence, data might become corrupted in case of host "
"crash.\n", file_name);
g_free(proc_link);
g_free(file_name);
}
/*
* if map failed with MAP_SHARED_VALIDATE | MAP_SYNC,
* we will remove these flags to handle compatibility.
*/
ptr = mmap(guardptr + offset, size, prot, flags, fd, 0);
}
if (ptr == MAP_FAILED) {
munmap(guardptr, total);
return MAP_FAILED;
}
if (offset > 0) {
munmap(guardptr, 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 + pagesize) {
munmap(ptr + size + pagesize, total - size - pagesize);
}
return ptr;
}
void qemu_ram_munmap(int fd, void *ptr, size_t size)
{
size_t pagesize;
if (ptr) {
/* Unmap both the RAM block and the guard page */
#if defined(__powerpc64__) && defined(__linux__)
pagesize = qemu_fd_getpagesize(fd);
#else
pagesize = qemu_real_host_page_size;
#endif
munmap(ptr, size + pagesize);
}
}
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