hugepage-mremap.c

  1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 * hugepage-mremap:
  4 *
  5 * Example of remapping huge page memory in a user application using the
  6 * mremap system call.  The path to a file in a hugetlbfs filesystem must
  7 * be passed as the last argument to this test.  The amount of memory used
  8 * by this test in MBs can optionally be passed as an argument.  If no memory
  9 * amount is passed, the default amount is 10MB.
 10 *
 11 * To make sure the test triggers pmd sharing and goes through the 'unshare'
 12 * path in the mremap code use 1GB (1024) or more.
 13 */
 14
 15#define _GNU_SOURCE
 16#include <stdlib.h>
 17#include <stdio.h>
 18#include <unistd.h>
 19#include <sys/mman.h>
 20#include <errno.h>
 21#include <fcntl.h> /* Definition of O_* constants */
 22#include <sys/syscall.h> /* Definition of SYS_* constants */
 23#include <linux/userfaultfd.h>
 24#include <sys/ioctl.h>
 25#include <string.h>
 26#include <stdbool.h>
 27#include "kselftest.h"
 28#include "vm_util.h"
 29
 30#define DEFAULT_LENGTH_MB 10UL
 31#define MB_TO_BYTES(x) (x * 1024 * 1024)
 32
 33#define PROTECTION (PROT_READ | PROT_WRITE | PROT_EXEC)
 34#define FLAGS (MAP_SHARED | MAP_ANONYMOUS)
 35
 36static void check_bytes(char *addr)
 37{
 38	ksft_print_msg("First hex is %x\n", *((unsigned int *)addr));
 39}
 40
 41static void write_bytes(char *addr, size_t len)
 42{
 43	unsigned long i;
 44
 45	for (i = 0; i < len; i++)
 46		*(addr + i) = (char)i;
 47}
 48
 49static int read_bytes(char *addr, size_t len)
 50{
 51	unsigned long i;
 52
 53	check_bytes(addr);
 54	for (i = 0; i < len; i++)
 55		if (*(addr + i) != (char)i) {
 56			ksft_print_msg("Mismatch at %lu\n", i);
 57			return 1;
 58		}
 59	return 0;
 60}
 61
 62static void register_region_with_uffd(char *addr, size_t len)
 63{
 64	long uffd; /* userfaultfd file descriptor */
 65	struct uffdio_api uffdio_api;
 66
 67	/* Create and enable userfaultfd object. */
 68	uffd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK);
 69	if (uffd == -1) {
 70		switch (errno) {
 71		case EPERM:
 72			ksft_exit_skip("Insufficient permissions, try running as root.\n");
 73			break;
 74		case ENOSYS:
 75			ksft_exit_skip("userfaultfd is not supported/not enabled.\n");
 76			break;
 77		default:
 78			ksft_exit_fail_msg("userfaultfd failed with %s\n", strerror(errno));
 79			break;
 80		}
 81	}
 82
 83	uffdio_api.api = UFFD_API;
 84	uffdio_api.features = 0;
 85	if (ioctl(uffd, UFFDIO_API, &uffdio_api) == -1)
 86		ksft_exit_fail_msg("ioctl-UFFDIO_API: %s\n", strerror(errno));
 87
 88	/* Create a private anonymous mapping. The memory will be
 89	 * demand-zero paged--that is, not yet allocated. When we
 90	 * actually touch the memory, it will be allocated via
 91	 * the userfaultfd.
 92	 */
 93
 94	addr = mmap(NULL, len, PROT_READ | PROT_WRITE,
 95		    MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
 96	if (addr == MAP_FAILED)
 97		ksft_exit_fail_msg("mmap: %s\n", strerror(errno));
 98
 99	ksft_print_msg("Address returned by mmap() = %p\n", addr);
100
101	/* Register the memory range of the mapping we just created for
102	 * handling by the userfaultfd object. In mode, we request to track
103	 * missing pages (i.e., pages that have not yet been faulted in).
104	 */
105	if (uffd_register(uffd, addr, len, true, false, false))
106		ksft_exit_fail_msg("ioctl-UFFDIO_REGISTER: %s\n", strerror(errno));
107}
108
109int main(int argc, char *argv[])
110{
111	size_t length = 0;
112	int ret = 0, fd;
113
114	ksft_print_header();
115	ksft_set_plan(1);
116
117	if (argc >= 2 && !strcmp(argv[1], "-h"))
118		ksft_exit_fail_msg("Usage: %s [length_in_MB]\n", argv[0]);
119
120	/* Read memory length as the first arg if valid, otherwise fallback to
121	 * the default length.
122	 */
123	if (argc >= 2)
124		length = (size_t)atoi(argv[1]);
125	else
126		length = DEFAULT_LENGTH_MB;
127
128	length = MB_TO_BYTES(length);
129	fd = memfd_create(argv[0], MFD_HUGETLB);
130	if (fd < 0)
131		ksft_exit_fail_msg("Open failed: %s\n", strerror(errno));
132
133	/* mmap to a PUD aligned address to hopefully trigger pmd sharing. */
134	unsigned long suggested_addr = 0x7eaa40000000;
135	void *haddr = mmap((void *)suggested_addr, length, PROTECTION,
136			   MAP_HUGETLB | MAP_SHARED | MAP_POPULATE, fd, 0);
137	ksft_print_msg("Map haddr: Returned address is %p\n", haddr);
138	if (haddr == MAP_FAILED)
139		ksft_exit_fail_msg("mmap1: %s\n", strerror(errno));
140
141	/* mmap again to a dummy address to hopefully trigger pmd sharing. */
142	suggested_addr = 0x7daa40000000;
143	void *daddr = mmap((void *)suggested_addr, length, PROTECTION,
144			   MAP_HUGETLB | MAP_SHARED | MAP_POPULATE, fd, 0);
145	ksft_print_msg("Map daddr: Returned address is %p\n", daddr);
146	if (daddr == MAP_FAILED)
147		ksft_exit_fail_msg("mmap3: %s\n", strerror(errno));
148
149	suggested_addr = 0x7faa40000000;
150	void *vaddr =
151		mmap((void *)suggested_addr, length, PROTECTION, FLAGS, -1, 0);
152	ksft_print_msg("Map vaddr: Returned address is %p\n", vaddr);
153	if (vaddr == MAP_FAILED)
154		ksft_exit_fail_msg("mmap2: %s\n", strerror(errno));
155
156	register_region_with_uffd(haddr, length);
157
158	void *addr = mremap(haddr, length, length,
159			    MREMAP_MAYMOVE | MREMAP_FIXED, vaddr);
160	if (addr == MAP_FAILED)
161		ksft_exit_fail_msg("mremap: %s\n", strerror(errno));
162
163	ksft_print_msg("Mremap: Returned address is %p\n", addr);
164	check_bytes(addr);
165	write_bytes(addr, length);
166	ret = read_bytes(addr, length);
167
168	munmap(addr, length);
169
170	addr = mremap(addr, length, length, 0);
171	if (addr != MAP_FAILED)
172		ksft_exit_fail_msg("mremap: Expected failure, but call succeeded\n");
173
174	close(fd);
175
176	ksft_test_result(!ret, "Read same data\n");
177	ksft_exit(!ret);
178}