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// SPDX-License-Identifier: GPL-2.0
/*
* hugepage-mremap:
*
* Example of remapping huge page memory in a user application using the
* mremap system call. Code assumes a hugetlbfs filesystem is mounted
* at './huge'. The code will use 10MB worth of huge pages.
*/
#define _GNU_SOURCE
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/mman.h>
#include <errno.h>
#include <fcntl.h> /* Definition of O_* constants */
#include <sys/syscall.h> /* Definition of SYS_* constants */
#include <linux/userfaultfd.h>
#include <sys/ioctl.h>
#define LENGTH (1UL * 1024 * 1024 * 1024)
#define PROTECTION (PROT_READ | PROT_WRITE | PROT_EXEC)
#define FLAGS (MAP_SHARED | MAP_ANONYMOUS)
static void check_bytes(char *addr)
{
printf("First hex is %x\n", *((unsigned int *)addr));
}
static void write_bytes(char *addr)
{
unsigned long i;
for (i = 0; i < LENGTH; i++)
*(addr + i) = (char)i;
}
static int read_bytes(char *addr)
{
unsigned long i;
check_bytes(addr);
for (i = 0; i < LENGTH; i++)
if (*(addr + i) != (char)i) {
printf("Mismatch at %lu\n", i);
return 1;
}
return 0;
}
static void register_region_with_uffd(char *addr, size_t len)
{
long uffd; /* userfaultfd file descriptor */
struct uffdio_api uffdio_api;
struct uffdio_register uffdio_register;
/* Create and enable userfaultfd object. */
uffd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK);
if (uffd == -1) {
perror("userfaultfd");
exit(1);
}
uffdio_api.api = UFFD_API;
uffdio_api.features = 0;
if (ioctl(uffd, UFFDIO_API, &uffdio_api) == -1) {
perror("ioctl-UFFDIO_API");
exit(1);
}
/* Create a private anonymous mapping. The memory will be
* demand-zero paged--that is, not yet allocated. When we
* actually touch the memory, it will be allocated via
* the userfaultfd.
*/
addr = mmap(NULL, len, PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
if (addr == MAP_FAILED) {
perror("mmap");
exit(1);
}
printf("Address returned by mmap() = %p\n", addr);
/* Register the memory range of the mapping we just created for
* handling by the userfaultfd object. In mode, we request to track
* missing pages (i.e., pages that have not yet been faulted in).
*/
uffdio_register.range.start = (unsigned long)addr;
uffdio_register.range.len = len;
uffdio_register.mode = UFFDIO_REGISTER_MODE_MISSING;
if (ioctl(uffd, UFFDIO_REGISTER, &uffdio_register) == -1) {
perror("ioctl-UFFDIO_REGISTER");
exit(1);
}
}
int main(void)
{
int ret = 0;
int fd = open("/huge/test", O_CREAT | O_RDWR, 0755);
if (fd < 0) {
perror("Open failed");
exit(1);
}
/* mmap to a PUD aligned address to hopefully trigger pmd sharing. */
unsigned long suggested_addr = 0x7eaa40000000;
void *haddr = mmap((void *)suggested_addr, LENGTH, PROTECTION,
MAP_HUGETLB | MAP_SHARED | MAP_POPULATE, fd, 0);
printf("Map haddr: Returned address is %p\n", haddr);
if (haddr == MAP_FAILED) {
perror("mmap1");
exit(1);
}
/* mmap again to a dummy address to hopefully trigger pmd sharing. */
suggested_addr = 0x7daa40000000;
void *daddr = mmap((void *)suggested_addr, LENGTH, PROTECTION,
MAP_HUGETLB | MAP_SHARED | MAP_POPULATE, fd, 0);
printf("Map daddr: Returned address is %p\n", daddr);
if (daddr == MAP_FAILED) {
perror("mmap3");
exit(1);
}
suggested_addr = 0x7faa40000000;
void *vaddr =
mmap((void *)suggested_addr, LENGTH, PROTECTION, FLAGS, -1, 0);
printf("Map vaddr: Returned address is %p\n", vaddr);
if (vaddr == MAP_FAILED) {
perror("mmap2");
exit(1);
}
register_region_with_uffd(haddr, LENGTH);
void *addr = mremap(haddr, LENGTH, LENGTH,
MREMAP_MAYMOVE | MREMAP_FIXED, vaddr);
if (addr == MAP_FAILED) {
perror("mremap");
exit(1);
}
printf("Mremap: Returned address is %p\n", addr);
check_bytes(addr);
write_bytes(addr);
ret = read_bytes(addr);
munmap(addr, LENGTH);
return ret;
}
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