1 files changed, 188 insertions, 0 deletions
diff --git a/tools/testing/selftests/mm/hugepage-mremap.c b/tools/testing/selftests/mm/hugepage-mremap.c
new file mode 100644
index 000000000000..e53b5eaa8fce
--- /dev/null
+++ b/tools/testing/selftests/mm/hugepage-mremap.c
@@ -0,0 +1,188 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * hugepage-mremap:
+ *
+ * Example of remapping huge page memory in a user application using the
+ * mremap system call.  The path to a file in a hugetlbfs filesystem must
+ * be passed as the last argument to this test.  The amount of memory used
+ * by this test in MBs can optionally be passed as an argument.  If no memory
+ * amount is passed, the default amount is 10MB.
+ *
+ * To make sure the test triggers pmd sharing and goes through the 'unshare'
+ * path in the mremap code use 1GB (1024) or more.
+ */
+
+#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>
+#include <string.h>
+
+#define DEFAULT_LENGTH_MB 10UL
+#define MB_TO_BYTES(x) (x * 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, size_t len)
+{
+	unsigned long i;
+
+	for (i = 0; i < len; i++)
+		*(addr + i) = (char)i;
+}
+
+static int read_bytes(char *addr, size_t len)
+{
+	unsigned long i;
+
+	check_bytes(addr);
+	for (i = 0; i < len; 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(int argc, char *argv[])
+{
+	size_t length = 0;
+	int ret = 0, fd;
+
+	if (argc >= 2 && !strcmp(argv[1], "-h")) {
+		printf("Usage: %s [length_in_MB]\n", argv[0]);
+		exit(1);
+	}
+
+	/* Read memory length as the first arg if valid, otherwise fallback to
+	 * the default length.
+	 */
+	if (argc >= 2)
+		length = (size_t)atoi(argv[1]);
+	else
+		length = DEFAULT_LENGTH_MB;
+
+	length = MB_TO_BYTES(length);
+	fd = memfd_create(argv[0], MFD_HUGETLB);
+	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, length);
+	ret = read_bytes(addr, length);
+
+	munmap(addr, length);
+
+	addr = mremap(addr, length, length, 0);
+	if (addr != MAP_FAILED) {
+		printf("mremap: Expected failure, but call succeeded\n");
+		exit(1);
+	}
+
+	close(fd);
+
+	return ret;
+}