selftests/mm: gup_longterm: new functional test for FOLL_LONGTERM

Let's add a new test for checking whether GUP long-term page pinning works
as expected (R/O vs.  R/W, MAP_PRIVATE vs.  MAP_SHARED, GUP vs. 
GUP-fast).  Note that COW handling with long-term R/O pinning in private
mappings, and pinning of anonymous memory in general, is tested by the COW
selftest.  This test, therefore, focuses on page pinning in file mappings.

The most interesting case is probably the "local tmpfile" case, as that
will likely end up on a "real" filesystem such as ext4 or xfs, not on a
virtual one like tmpfs or hugetlb where any long-term page pinning is
always expected to succeed.

For now, only add tests that use the "/sys/kernel/debug/gup_test"
interface.  We'll add tests based on liburing separately next.

[akpm@linux-foundation.org: update .gitignore for gup_longterm, per Peter]
Link: https://lkml.kernel.org/r/20230519102723.185721-3-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

tools/testing/selftests/mm/.gitignore

@@ -39,3 +39,4 @@ local_config.h
 local_config.mk
 ksm_functional_tests
 mdwe_test
+gup_longterm

tools/testing/selftests/mm/Makefile

@@ -34,6 +34,7 @@ LDLIBS = -lrt -lpthread
 
 TEST_GEN_PROGS = cow
 TEST_GEN_PROGS += compaction_test
+TEST_GEN_PROGS += gup_longterm
 TEST_GEN_PROGS += gup_test
 TEST_GEN_PROGS += hmm-tests
 TEST_GEN_PROGS += hugetlb-madvise
@@ -164,6 +165,8 @@ endif
 # IOURING_EXTRA_LIBS may get set in local_config.mk, or it may be left empty.
 $(OUTPUT)/cow: LDLIBS += $(IOURING_EXTRA_LIBS)
 
+$(OUTPUT)/gup_longterm: LDLIBS += $(IOURING_EXTRA_LIBS)
+
 $(OUTPUT)/mlock-random-test $(OUTPUT)/memfd_secret: LDLIBS += -lcap
 
 $(OUTPUT)/ksm_tests: LDLIBS += -lnuma

tools/testing/selftests/mm/gup_longterm.c

@@ -0,0 +1,386 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * GUP long-term page pinning tests.
+ *
+ * Copyright 2023, Red Hat, Inc.
+ *
+ * Author(s): David Hildenbrand <david@redhat.com>
+ */
+#define _GNU_SOURCE
+#include <stdlib.h>
+#include <string.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <unistd.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <assert.h>
+#include <sys/mman.h>
+#include <sys/ioctl.h>
+#include <sys/vfs.h>
+#include <linux/magic.h>
+#include <linux/memfd.h>
+
+#include "local_config.h"
+
+#include "../../../../mm/gup_test.h"
+#include "../kselftest.h"
+#include "vm_util.h"
+
+static size_t pagesize;
+static int nr_hugetlbsizes;
+static size_t hugetlbsizes[10];
+static int gup_fd;
+
+static __fsword_t get_fs_type(int fd)
+{
+	struct statfs fs;
+	int ret;
+
+	do {
+		ret = fstatfs(fd, &fs);
+	} while (ret && errno == EINTR);
+
+	return ret ? 0 : fs.f_type;
+}
+
+static bool fs_is_unknown(__fsword_t fs_type)
+{
+	/*
+	 * We only support some filesystems in our tests when dealing with
+	 * R/W long-term pinning. For these filesystems, we can be fairly sure
+	 * whether they support it or not.
+	 */
+	switch (fs_type) {
+	case TMPFS_MAGIC:
+	case HUGETLBFS_MAGIC:
+	case BTRFS_SUPER_MAGIC:
+	case EXT4_SUPER_MAGIC:
+	case XFS_SUPER_MAGIC:
+		return false;
+	default:
+		return true;
+	}
+}
+
+static bool fs_supports_writable_longterm_pinning(__fsword_t fs_type)
+{
+	assert(!fs_is_unknown(fs_type));
+	switch (fs_type) {
+	case TMPFS_MAGIC:
+	case HUGETLBFS_MAGIC:
+		return true;
+	default:
+		return false;
+	}
+}
+
+enum test_type {
+	TEST_TYPE_RO,
+	TEST_TYPE_RO_FAST,
+	TEST_TYPE_RW,
+	TEST_TYPE_RW_FAST,
+};
+
+static void do_test(int fd, size_t size, enum test_type type, bool shared)
+{
+	__fsword_t fs_type = get_fs_type(fd);
+	bool should_work;
+	char *mem;
+	int ret;
+
+	if (ftruncate(fd, size)) {
+		ksft_test_result_fail("ftruncate() failed\n");
+		return;
+	}
+
+	if (fallocate(fd, 0, 0, size)) {
+		if (size == pagesize)
+			ksft_test_result_fail("fallocate() failed\n");
+		else
+			ksft_test_result_skip("need more free huge pages\n");
+		return;
+	}
+
+	mem = mmap(NULL, size, PROT_READ | PROT_WRITE,
+		   shared ? MAP_SHARED : MAP_PRIVATE, fd, 0);
+	if (mem == MAP_FAILED) {
+		if (size == pagesize || shared)
+			ksft_test_result_fail("mmap() failed\n");
+		else
+			ksft_test_result_skip("need more free huge pages\n");
+		return;
+	}
+
+	/*
+	 * Fault in the page writable such that GUP-fast can eventually pin
+	 * it immediately.
+	 */
+	memset(mem, 0, size);
+
+	switch (type) {
+	case TEST_TYPE_RO:
+	case TEST_TYPE_RO_FAST:
+	case TEST_TYPE_RW:
+	case TEST_TYPE_RW_FAST: {
+		struct pin_longterm_test args;
+		const bool fast = type == TEST_TYPE_RO_FAST ||
+				  type == TEST_TYPE_RW_FAST;
+		const bool rw = type == TEST_TYPE_RW ||
+				type == TEST_TYPE_RW_FAST;
+
+		if (gup_fd < 0) {
+			ksft_test_result_skip("gup_test not available\n");
+			break;
+		}
+
+		if (rw && shared && fs_is_unknown(fs_type)) {
+			ksft_test_result_skip("Unknown filesystem\n");
+			return;
+		}
+		/*
+		 * R/O pinning or pinning in a private mapping is always
+		 * expected to work. Otherwise, we expect long-term R/W pinning
+		 * to only succeed for special fielesystems.
+		 */
+		should_work = !shared || !rw ||
+			      fs_supports_writable_longterm_pinning(fs_type);
+
+		args.addr = (__u64)(uintptr_t)mem;
+		args.size = size;
+		args.flags = fast ? PIN_LONGTERM_TEST_FLAG_USE_FAST : 0;
+		args.flags |= rw ? PIN_LONGTERM_TEST_FLAG_USE_WRITE : 0;
+		ret = ioctl(gup_fd, PIN_LONGTERM_TEST_START, &args);
+		if (ret && errno == EINVAL) {
+			ksft_test_result_skip("PIN_LONGTERM_TEST_START failed\n");
+			break;
+		} else if (ret && errno == EFAULT) {
+			ksft_test_result(!should_work, "Should have failed\n");
+			break;
+		} else if (ret) {
+			ksft_test_result_fail("PIN_LONGTERM_TEST_START failed\n");
+			break;
+		}
+
+		if (ioctl(gup_fd, PIN_LONGTERM_TEST_STOP))
+			ksft_print_msg("[INFO] PIN_LONGTERM_TEST_STOP failed\n");
+
+		/*
+		 * TODO: if the kernel ever supports long-term R/W pinning on
+		 * some previously unsupported filesystems, we might want to
+		 * perform some additional tests for possible data corruptions.
+		 */
+		ksft_test_result(should_work, "Should have worked\n");
+		break;
+	}
+	default:
+		assert(false);
+	}
+
+	munmap(mem, size);
+}
+
+typedef void (*test_fn)(int fd, size_t size);
+
+static void run_with_memfd(test_fn fn, const char *desc)
+{
+	int fd;
+
+	ksft_print_msg("[RUN] %s ... with memfd\n", desc);
+
+	fd = memfd_create("test", 0);
+	if (fd < 0) {
+		ksft_test_result_fail("memfd_create() failed\n");
+		return;
+	}
+
+	fn(fd, pagesize);
+	close(fd);
+}
+
+static void run_with_tmpfile(test_fn fn, const char *desc)
+{
+	FILE *file;
+	int fd;
+
+	ksft_print_msg("[RUN] %s ... with tmpfile\n", desc);
+
+	file = tmpfile();
+	if (!file) {
+		ksft_test_result_fail("tmpfile() failed\n");
+		return;
+	}
+
+	fd = fileno(file);
+	if (fd < 0) {
+		ksft_test_result_fail("fileno() failed\n");
+		return;
+	}
+
+	fn(fd, pagesize);
+	fclose(file);
+}
+
+static void run_with_local_tmpfile(test_fn fn, const char *desc)
+{
+	char filename[] = __FILE__"_tmpfile_XXXXXX";
+	int fd;
+
+	ksft_print_msg("[RUN] %s ... with local tmpfile\n", desc);
+
+	fd = mkstemp(filename);
+	if (fd < 0) {
+		ksft_test_result_fail("mkstemp() failed\n");
+		return;
+	}
+
+	if (unlink(filename)) {
+		ksft_test_result_fail("unlink() failed\n");
+		goto close;
+	}
+
+	fn(fd, pagesize);
+close:
+	close(fd);
+}
+
+static void run_with_memfd_hugetlb(test_fn fn, const char *desc,
+				   size_t hugetlbsize)
+{
+	int flags = MFD_HUGETLB;
+	int fd;
+
+	ksft_print_msg("[RUN] %s ... with memfd hugetlb (%zu kB)\n", desc,
+		       hugetlbsize / 1024);
+
+	flags |= __builtin_ctzll(hugetlbsize) << MFD_HUGE_SHIFT;
+
+	fd = memfd_create("test", flags);
+	if (fd < 0) {
+		ksft_test_result_skip("memfd_create() failed\n");
+		return;
+	}
+
+	fn(fd, hugetlbsize);
+	close(fd);
+}
+
+struct test_case {
+	const char *desc;
+	test_fn fn;
+};
+
+static void test_shared_rw_pin(int fd, size_t size)
+{
+	do_test(fd, size, TEST_TYPE_RW, true);
+}
+
+static void test_shared_rw_fast_pin(int fd, size_t size)
+{
+	do_test(fd, size, TEST_TYPE_RW_FAST, true);
+}
+
+static void test_shared_ro_pin(int fd, size_t size)
+{
+	do_test(fd, size, TEST_TYPE_RO, true);
+}
+
+static void test_shared_ro_fast_pin(int fd, size_t size)
+{
+	do_test(fd, size, TEST_TYPE_RO_FAST, true);
+}
+
+static void test_private_rw_pin(int fd, size_t size)
+{
+	do_test(fd, size, TEST_TYPE_RW, false);
+}
+
+static void test_private_rw_fast_pin(int fd, size_t size)
+{
+	do_test(fd, size, TEST_TYPE_RW_FAST, false);
+}
+
+static void test_private_ro_pin(int fd, size_t size)
+{
+	do_test(fd, size, TEST_TYPE_RO, false);
+}
+
+static void test_private_ro_fast_pin(int fd, size_t size)
+{
+	do_test(fd, size, TEST_TYPE_RO_FAST, false);
+}
+
+static const struct test_case test_cases[] = {
+	{
+		"R/W longterm GUP pin in MAP_SHARED file mapping",
+		test_shared_rw_pin,
+	},
+	{
+		"R/W longterm GUP-fast pin in MAP_SHARED file mapping",
+		test_shared_rw_fast_pin,
+	},
+	{
+		"R/O longterm GUP pin in MAP_SHARED file mapping",
+		test_shared_ro_pin,
+	},
+	{
+		"R/O longterm GUP-fast pin in MAP_SHARED file mapping",
+		test_shared_ro_fast_pin,
+	},
+	{
+		"R/W longterm GUP pin in MAP_PRIVATE file mapping",
+		test_private_rw_pin,
+	},
+	{
+		"R/W longterm GUP-fast pin in MAP_PRIVATE file mapping",
+		test_private_rw_fast_pin,
+	},
+	{
+		"R/O longterm GUP pin in MAP_PRIVATE file mapping",
+		test_private_ro_pin,
+	},
+	{
+		"R/O longterm GUP-fast pin in MAP_PRIVATE file mapping",
+		test_private_ro_fast_pin,
+	},
+};
+
+static void run_test_case(struct test_case const *test_case)
+{
+	int i;
+
+	run_with_memfd(test_case->fn, test_case->desc);
+	run_with_tmpfile(test_case->fn, test_case->desc);
+	run_with_local_tmpfile(test_case->fn, test_case->desc);
+	for (i = 0; i < nr_hugetlbsizes; i++)
+		run_with_memfd_hugetlb(test_case->fn, test_case->desc,
+				       hugetlbsizes[i]);
+}
+
+static int tests_per_test_case(void)
+{
+	return 3 + nr_hugetlbsizes;
+}
+
+int main(int argc, char **argv)
+{
+	int i, err;
+
+	pagesize = getpagesize();
+	nr_hugetlbsizes = detect_hugetlb_page_sizes(hugetlbsizes,
+						    ARRAY_SIZE(hugetlbsizes));
+
+	ksft_print_header();
+	ksft_set_plan(ARRAY_SIZE(test_cases) * tests_per_test_case());
+
+	gup_fd = open("/sys/kernel/debug/gup_test", O_RDWR);
+
+	for (i = 0; i < ARRAY_SIZE(test_cases); i++)
+		run_test_case(&test_cases[i]);
+
+	err = ksft_get_fail_cnt();
+	if (err)
+		ksft_exit_fail_msg("%d out of %d tests failed\n",
+				   err, ksft_test_num());
+	return ksft_exit_pass();
+}

tools/testing/selftests/mm/run_vmtests.sh

@@ -24,7 +24,7 @@ separated by spaces:
 - mmap
 	tests for mmap(2)
 - gup_test
-	tests for gup using gup_test interface
+	tests for gup
 - userfaultfd
 	tests for  userfaultfd(2)
 - compaction
@@ -196,6 +196,8 @@ CATEGORY="gup_test" run_test ./gup_test -a
 # Dump pages 0, 19, and 4096, using pin_user_pages:
 CATEGORY="gup_test" run_test ./gup_test -ct -F 0x1 0 19 0x1000
 
+CATEGORY="gup_test" run_test ./gup_longterm
+
 CATEGORY="userfaultfd" run_test ./uffd-unit-tests
 uffd_stress_bin=./uffd-stress
 CATEGORY="userfaultfd" run_test ${uffd_stress_bin} anon 20 16