[RESEND v7 29/29] selftests/mm: add PMD swap entry tests

[Usama Arif <usama.arif@linux.dev>]

Each test gets a fresh PMD-mapped THP from fixture setup, fills it with a
pattern that differs between base pages so a reordered split is detectable,
swaps it out with MADV_PAGEOUT, and verifies thp_swpout_pmd increased
before the test body runs.

The tests are basic, swapin_sync, fork, fork_cow, write, rwp_swapin,
munmap, mprotect, split_mprotect, split_munmap, uffdio_move, mremap,
pagemap, mincore, madvise_free, madvise_willneed and swapoff.

MADV_PAGEOUT leaves the folio in the swap cache on an asynchronous device,
so a fault would only remap it and never reach swapin_sync(). Fixture setup
therefore asks the current cgroup to reclaim afterwards, and uses mincore()
- which reports a PMD swap entry as resident exactly while the cache holds
it - to tell whether that worked. Tests run either way; swapin_sync skips
if the cache survived. The swapoff test runs only when PMD_SWAP_DEVICE is
the sole active swap device, and restores it at its original priority.

Skip rather than fail where the kernel never promised anything.
thp_swpout_pmd and thp_swpout_fallback are system-wide, so test the
fallback counter first: if reclaim split any THP we cannot be sure it was
not ours. That also covers a kernel without CONFIG_THP_SWAP. A kernel with
no thp_swpout_pmd counter does not implement the feature at all.

With zswap enabled the range may legitimately come back through the PTE
fallback, so those runs skip the PMD-restoration assertions and say so.

Add a /proc/vmstat field reader to vm_util.c so other tests can use it too,
and register pmd_swap with run_vmtests.sh and the default runner.

Assisted-by: LLM
Signed-off-by: Usama Arif <usama.arif@linux.dev>
---
 tools/testing/selftests/mm/Makefile         |   2 +
 tools/testing/selftests/mm/ksft_pmd_swap.sh |   4 +
 tools/testing/selftests/mm/pmd_swap.c       | 989 ++++++++++++++++++++
 tools/testing/selftests/mm/run_vmtests.sh   |   4 +
 tools/testing/selftests/mm/vm_util.c        |  24 +
 tools/testing/selftests/mm/vm_util.h        |   2 +
 6 files changed, 1025 insertions(+)
 create mode 100755 tools/testing/selftests/mm/ksft_pmd_swap.sh
 create mode 100644 tools/testing/selftests/mm/pmd_swap.c

diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile
index d3e9bd67904aa..a685988a3d569 100644
--- a/tools/testing/selftests/mm/Makefile
+++ b/tools/testing/selftests/mm/Makefile
@@ -104,6 +104,7 @@ TEST_GEN_FILES += guard-regions
 TEST_GEN_FILES += merge
 TEST_GEN_FILES += rmap
 TEST_GEN_FILES += folio_split_race_test
+TEST_GEN_FILES += pmd_swap
 TEST_GEN_FILES += soft-dirty
 
 ifeq ($(ARCH),x86_64)
@@ -162,6 +163,7 @@ TEST_PROGS += ksft_mremap.sh
 TEST_PROGS += ksft_pagemap.sh
 TEST_PROGS += ksft_pfnmap.sh
 TEST_PROGS += ksft_pkey.sh
+TEST_PROGS += ksft_pmd_swap.sh
 TEST_PROGS += ksft_process_madv.sh
 TEST_PROGS += ksft_process_mrelease.sh
 TEST_PROGS += ksft_rmap.sh
diff --git a/tools/testing/selftests/mm/ksft_pmd_swap.sh b/tools/testing/selftests/mm/ksft_pmd_swap.sh
new file mode 100755
index 0000000000000..0f070b4729a89
--- /dev/null
+++ b/tools/testing/selftests/mm/ksft_pmd_swap.sh
@@ -0,0 +1,4 @@
+#!/bin/sh -e
+# SPDX-License-Identifier: GPL-2.0
+
+./run_vmtests.sh -t pmd_swap
diff --git a/tools/testing/selftests/mm/pmd_swap.c b/tools/testing/selftests/mm/pmd_swap.c
new file mode 100644
index 0000000000000..91bac9ae5560e
--- /dev/null
+++ b/tools/testing/selftests/mm/pmd_swap.c
@@ -0,0 +1,989 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Test PMD-level swap entries and their users. */
+#define _GNU_SOURCE
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/mman.h>
+#include <sys/wait.h>
+#include <fcntl.h>
+#include <errno.h>
+#include <stdint.h>
+#include <sys/random.h>
+#include <sys/stat.h>
+#include <sys/swap.h>
+#include <sys/syscall.h>
+#include <sys/ioctl.h>
+#include <poll.h>
+#include <pthread.h>
+#include <linux/userfaultfd.h>
+#include <time.h>
+
+#include "kselftest_harness.h"
+#include "vm_util.h"
+
+#define ZSWAP_ENABLED_PATH "/sys/module/zswap/parameters/enabled"
+
+/* pagemap: bits 0-54 hold the PFN, or type|offset for a swap entry. */
+#define PM_PFRAME_MASK		((1ULL << 55) - 1)
+/* Must match MAX_SWAPFILES_SHIFT in include/linux/swap.h. */
+#define MAX_SWAPFILES_SHIFT	5
+
+static bool check_swapped(int pagemap_fd, char *addr, unsigned long size)
+{
+	unsigned long off;
+
+	for (off = 0; off < size; off += getpagesize())
+		if (!pagemap_is_swapped(pagemap_fd, addr + off))
+			return false;
+	return true;
+}
+
+static bool zswap_enabled(void)
+{
+	char enabled = 0;
+	FILE *f;
+
+	f = fopen(ZSWAP_ENABLED_PATH, "r");
+	if (!f)
+		return false;
+
+	if (fscanf(f, " %c", &enabled) != 1)
+		enabled = 0;
+	fclose(f);
+
+	return enabled == 'Y' || enabled == 'y' || enabled == '1';
+}
+
+static bool swap_available(unsigned long required_bytes)
+{
+	unsigned long required_kb = (required_bytes + 1023) / 1024;
+	unsigned long size_kb, used_kb;
+	char line[256];
+	bool ret = false;
+	FILE *f;
+
+	f = fopen("/proc/swaps", "r");
+	if (!f)
+		return false;
+
+	/* Skip the header. */
+	if (!fgets(line, sizeof(line), f))
+		goto out;
+
+	while (fgets(line, sizeof(line), f)) {
+		if (sscanf(line, "%*s %*s %lu %lu", &size_kb, &used_kb) == 2 &&
+		    size_kb >= used_kb && size_kb - used_kb >= required_kb) {
+			ret = true;
+			break;
+		}
+	}
+
+out:
+	fclose(f);
+	return ret;
+}
+
+static bool same_swap_device(const struct stat *a, const struct stat *b)
+{
+	if (S_ISBLK(a->st_mode) && S_ISBLK(b->st_mode))
+		return a->st_rdev == b->st_rdev;
+	return a->st_dev == b->st_dev && a->st_ino == b->st_ino;
+}
+
+/*
+ * Returns true if @swap_dev is the one and only active swap device, and stores
+ * its /proc/swaps priority in *prio so the caller can put it back the way it
+ * found it.
+ */
+static bool swap_device_is_only_active(const char *swap_dev, int *prio)
+{
+	struct stat expected, active;
+	char path[256], line[512];
+	unsigned int nr_active = 0;
+	bool matches = false;
+	FILE *f;
+
+	*prio = -1;
+
+	if (stat(swap_dev, &expected))
+		return false;
+
+	f = fopen("/proc/swaps", "r");
+	if (!f)
+		return false;
+	if (!fgets(line, sizeof(line), f))
+		goto out;
+
+	while (fgets(line, sizeof(line), f)) {
+		int line_prio;
+
+		if (sscanf(line, "%255s %*s %*s %*s %d", path, &line_prio) != 2)
+			continue;
+		nr_active++;
+		if (nr_active > 1)
+			goto out;
+		matches = !stat(path, &active) &&
+			  same_swap_device(&expected, &active);
+		if (matches)
+			*prio = line_prio;
+	}
+
+out:
+	fclose(f);
+	return nr_active == 1 && matches;
+}
+
+/* Re-enable a device swapoff()ed by this test, at its original priority. */
+static int swapon_restore(const char *swap_dev, int prio)
+{
+	int flags = 0;
+
+	if (prio >= 0)
+		flags = SWAP_FLAG_PREFER |
+			((prio << SWAP_FLAG_PRIO_SHIFT) & SWAP_FLAG_PRIO_MASK);
+	return swapon(swap_dev, flags);
+}
+
+/* Locate this task's cgroup-v2 directory. An empty relative path is the root. */
+static bool cgroup2_self_dir(char *buf, size_t len)
+{
+	char mnt[PATH_MAX] = "", type[64], rel[PATH_MAX] = "";
+	char line[2 * PATH_MAX];
+	size_t rel_len;
+	FILE *f;
+
+	f = fopen("/proc/self/mounts", "r");
+	if (!f)
+		return false;
+	while (fgets(line, sizeof(line), f)) {
+		if (sscanf(line, "%*s %4095s %63s", mnt, type) == 2 &&
+		    !strcmp(type, "cgroup2"))
+			goto found_mnt;
+	}
+	mnt[0] = '\0';
+found_mnt:
+	fclose(f);
+	if (!mnt[0])
+		return false;
+
+	f = fopen("/proc/self/cgroup", "r");
+	if (!f)
+		return false;
+	while (fgets(line, sizeof(line), f)) {
+		if (strncmp(line, "0::", 3))
+			continue;
+		rel_len = strcspn(line + 3, "\n");
+		if (rel_len && rel_len < sizeof(rel)) {
+			memcpy(rel, line + 3, rel_len);
+			rel[rel_len] = '\0';
+		}
+		break;
+	}
+	fclose(f);
+	if (!rel[0])
+		return false;
+	if (!strcmp(rel, "/"))
+		rel[0] = '\0';
+	return snprintf(buf, len, "%s%s/memory.reclaim", mnt, rel) < (int)len;
+}
+
+static bool cgroup_reclaim(unsigned long bytes)
+{
+	char path[PATH_MAX], val[32];
+	ssize_t written;
+	int fd, len, err;
+
+	if (!cgroup2_self_dir(path, sizeof(path)))
+		return false;
+
+	fd = open(path, O_WRONLY);
+	if (fd < 0)
+		return false;
+	len = snprintf(val, sizeof(val), "%lu", bytes);
+	written = write(fd, val, len);
+	err = errno;
+	close(fd);
+	/* -EAGAIN means it reclaimed something but fell short, which is fine. */
+	return written == len || err == EAGAIN;
+}
+
+/*
+ * mincore() reports 1 over a PMD swap entry iff the swap cache still holds it.
+ * This samples the first slot only: it is a hint used to decide whether the
+ * swap cache was evicted, not an assertion about the whole range.
+ */
+static bool swapcache_resident(char *mem)
+{
+	unsigned char vec[1];
+
+	if (mincore(mem, getpagesize(), vec))
+		return true;
+	return vec[0] & 1;
+}
+
+/*
+ * MADV_PAGEOUT leaves the folio in the swap cache on asynchronous swap
+ * devices, so faulting would just remap the cached folio and never reach
+ * swapin_sync(). Push it out so the PMD-order swap-in path is exercised.
+ */
+static bool drop_swapcache(char *mem, unsigned long pmd_size)
+{
+	unsigned long want = pmd_size;
+	int i;
+
+	for (i = 0; i < 3 && swapcache_resident(mem); i++, want *= 4)
+		if (!cgroup_reclaim(want))
+			break;
+	return !swapcache_resident(mem);
+}
+
+static unsigned int random_seed(void)
+{
+	unsigned int seed;
+
+	if (getrandom(&seed, sizeof(seed), 0) != sizeof(seed))
+		seed = (unsigned int)time(NULL);
+	return seed;
+}
+
+static unsigned long test_page_size(void)
+{
+	static unsigned long page_size;
+
+	if (!page_size)
+		page_size = getpagesize();
+	return page_size;
+}
+
+/*
+ * Two base pages of the same PMD must never hold identical bytes, or the split
+ * tests cannot tell that the slots came back in the wrong order. A single byte
+ * cannot encode a page index on its own - HPAGE_PMD_NR is 8192 on arm64 with
+ * 64K pages - so spell the index out in the first two bytes of every page.
+ */
+static unsigned char pattern_byte(unsigned int seed, unsigned long off)
+{
+	unsigned long page_size = test_page_size();
+	unsigned long idx = off & (page_size - 1);
+
+	if (idx < 2)
+		return (unsigned char)(seed + ((off / page_size) >> (idx * 8)));
+
+	return (unsigned char)(seed + off + (off >> 8) + (off >> 16));
+}
+
+static void fill_pattern(char *buf, unsigned long size, unsigned int seed)
+{
+	unsigned long i;
+
+	for (i = 0; i < size; i++)
+		buf[i] = (char)pattern_byte(seed, i);
+}
+
+static bool verify_pattern_range(char *buf, unsigned long size,
+				 unsigned int seed, unsigned long offset)
+{
+	unsigned long i;
+
+	for (i = 0; i < size; i++)
+		if ((unsigned char)buf[i] != pattern_byte(seed, offset + i))
+			return false;
+	return true;
+}
+
+static bool verify_pattern(char *buf, unsigned long size, unsigned int seed)
+{
+	return verify_pattern_range(buf, size, seed, 0);
+}
+
+static bool verify_zero(char *buf, unsigned long size)
+{
+	unsigned long i;
+
+	for (i = 0; i < size; i++)
+		if (buf[i])
+			return false;
+	return true;
+}
+
+/*
+ * mmap an anonymous PMD-aligned region of pmd_size bytes. Over-allocates
+ * by one PMD and trims the unaligned head/tail so the returned address is
+ * PMD-aligned (required for whole-PMD UFFDIO_MOVE).
+ */
+static char *mmap_pmd_aligned(unsigned long pmd_size)
+{
+	unsigned long pad = pmd_size;
+	char *raw, *aligned;
+
+	raw = mmap(NULL, pmd_size + pad, PROT_READ | PROT_WRITE,
+		   MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+	if (raw == MAP_FAILED)
+		return MAP_FAILED;
+
+	aligned = (char *)(((uintptr_t)raw + pmd_size - 1) & ~(pmd_size - 1));
+	if (aligned != raw)
+		munmap(raw, aligned - raw);
+	if (aligned + pmd_size != raw + pmd_size + pad)
+		munmap(aligned + pmd_size,
+		       (raw + pmd_size + pad) - (aligned + pmd_size));
+	return aligned;
+}
+
+/* Per-process swapped size in bytes, from /proc/self/status VmSwap. */
+static unsigned long read_vmswap(void)
+{
+	char line[256];
+	unsigned long kb = 0;
+	FILE *f;
+
+	f = fopen("/proc/self/status", "r");
+	if (!f)
+		return 0;
+	while (fgets(line, sizeof(line), f)) {
+		if (!strncmp(line, "VmSwap:", 7)) {
+			kb = strtoul(line + 7, NULL, 10);
+			break;
+		}
+	}
+	fclose(f);
+	return kb * 1024;
+}
+
+/*
+ * Swap the PMD range out. Returns true if a PMD swap entry was installed.
+ * On failure *swap_failed is set unless this environment simply cannot swap
+ * at PMD granularity, in which case the caller should skip rather than fail.
+ */
+static bool swap_out_pmd(char *mem, unsigned long pmd_size, int pagemap_fd,
+			 bool *swap_failed)
+{
+	long pmd_before = read_vmstat("thp_swpout_pmd");
+	long fallback_before = read_vmstat("thp_swpout_fallback");
+	long pmd_after, fallback_after;
+	bool swapped;
+
+	/*
+	 * A kernel without PMD swap entry support has no thp_swpout_pmd at
+	 * all. Skip rather than report a failure the kernel never promised.
+	 */
+	if (pmd_before < 0 || fallback_before < 0) {
+		ksft_print_msg("no thp_swpout_pmd counter; PMD swap entries unsupported\n");
+		return false;
+	}
+
+	if (madvise(mem, pmd_size, MADV_PAGEOUT)) {
+		ksft_print_msg("MADV_PAGEOUT failed: %s\n", strerror(errno));
+		*swap_failed = true;
+		return false;
+	}
+
+	swapped = check_swapped(pagemap_fd, mem, pmd_size);
+	pmd_after = read_vmstat("thp_swpout_pmd");
+	fallback_after = read_vmstat("thp_swpout_fallback");
+	ksft_print_msg("thp_swpout_pmd: %ld -> %ld, fallback: %ld -> %ld\n",
+		       pmd_before, pmd_after, fallback_before, fallback_after);
+
+	if (!swapped) {
+		ksft_print_msg("MADV_PAGEOUT did not swap the whole PMD range\n");
+		*swap_failed = true;
+		return false;
+	}
+	/*
+	 * Both counters are system-wide, so another task swapping a THP during
+	 * the window above can move either of them. Test the fallback counter
+	 * first: if reclaim split *any* THP we cannot be sure ours was not the
+	 * one, and skipping is the safe direction. That also covers a kernel
+	 * built without CONFIG_THP_SWAP, where folio_alloc_swap() returns
+	 * -E2BIG for every PMD-order folio.
+	 */
+	if (fallback_after > fallback_before) {
+		ksft_print_msg("PMD swap unavailable; reclaim used PTE fallback\n");
+		return false;
+	}
+	if (pmd_after > pmd_before)
+		return true;
+
+	*swap_failed = true;
+	return false;
+}
+
+static char *alloc_fill_swap_thp(unsigned long pmd_size, int pagemap_fd,
+				 unsigned int seed, bool *swap_failed)
+{
+	char *mem;
+
+	*swap_failed = false;
+
+	mem = mmap_pmd_aligned(pmd_size);
+	if (mem == MAP_FAILED)
+		return MAP_FAILED;
+
+	if (madvise(mem, pmd_size, MADV_HUGEPAGE)) {
+		ksft_print_msg("MADV_HUGEPAGE failed: %s\n", strerror(errno));
+		munmap(mem, pmd_size);
+		return MAP_FAILED;
+	}
+	fill_pattern(mem, pmd_size, seed);
+
+	if (!check_huge_anon(mem, pmd_size, 1, pmd_size)) {
+		munmap(mem, pmd_size);
+		return MAP_FAILED;
+	}
+	if (!swap_out_pmd(mem, pmd_size, pagemap_fd, swap_failed)) {
+		munmap(mem, pmd_size);
+		return MAP_FAILED;
+	}
+
+	return mem;
+}
+
+struct rwp_access_args {
+	unsigned char *addr;
+	unsigned char expected;
+	bool write;
+	bool ok;
+};
+
+static void *rwp_access_thread(void *data)
+{
+	struct rwp_access_args *args = data;
+
+	if (args->write)
+		*args->addr = args->expected;
+	args->ok = *args->addr == args->expected;
+	return NULL;
+}
+
+static int register_rwp(char *addr, unsigned long size, bool protect)
+{
+	struct uffdio_register reg = {};
+	struct uffdio_rwprotect rwp = {};
+	struct uffdio_api api = {};
+	int uffd;
+
+	uffd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK);
+	if (uffd < 0)
+		return -1;
+
+	api.api = UFFD_API;
+	api.features = UFFD_FEATURE_RWP;
+	if (ioctl(uffd, UFFDIO_API, &api) ||
+	    !(api.features & UFFD_FEATURE_RWP))
+		goto error;
+
+	reg.range.start = (unsigned long)addr;
+	reg.range.len = size;
+	reg.mode = UFFDIO_REGISTER_MODE_RWP;
+	if (ioctl(uffd, UFFDIO_REGISTER, &reg))
+		goto error;
+
+	if (!protect)
+		return uffd;
+
+	rwp.range.start = (unsigned long)addr;
+	rwp.range.len = size;
+	rwp.mode = UFFDIO_RWPROTECT_MODE_RWP;
+	if (!ioctl(uffd, UFFDIO_RWPROTECT, &rwp))
+		return uffd;
+
+error:
+	close(uffd);
+	return -1;
+}
+
+static bool expect_rwp_fault(int uffd, char *addr, unsigned long size,
+			     unsigned char expected, bool write)
+{
+	struct rwp_access_args args = {
+		.addr = (unsigned char *)addr,
+		.expected = expected,
+		.write = write,
+	};
+	struct uffdio_rwprotect rwp = {
+		.range = {
+			.start = (unsigned long)addr,
+			.len = size,
+		},
+	};
+	struct pollfd pollfd = {
+		.fd = uffd,
+		.events = POLLIN,
+	};
+	struct uffd_msg msg = {};
+	pthread_t thread;
+	bool saw_rwp = false;
+	int ret;
+
+	if (pthread_create(&thread, NULL, rwp_access_thread, &args))
+		return false;
+
+	ret = poll(&pollfd, 1, 5000);
+	if (ret == 1 && (pollfd.revents & POLLIN) &&
+	    read(uffd, &msg, sizeof(msg)) == (ssize_t)sizeof(msg)) {
+		saw_rwp = msg.event == UFFD_EVENT_PAGEFAULT &&
+			  (msg.arg.pagefault.flags & UFFD_PAGEFAULT_FLAG_RWP);
+	}
+
+	/* Resolve the access even on failure so the worker cannot remain blocked. */
+	ioctl(uffd, UFFDIO_RWPROTECT, &rwp);
+	if (pthread_join(thread, NULL))
+		return false;
+	return saw_rwp && args.ok;
+}
+
+FIXTURE(pmd_swap)
+{
+	unsigned long pmd_size;
+	unsigned long mem_len;
+	int pagemap_fd;
+	int uffd;
+	unsigned int seed;
+	bool zswap_enabled;
+	bool swap_disabled;
+	int swap_prio;
+	bool swapcache_dropped;
+	const char *swap_dev;
+	char *mem;
+	char *aux;
+};
+
+FIXTURE_SETUP(pmd_swap)
+{
+	bool swap_failed;
+
+	self->pagemap_fd = -1;
+	self->uffd = -1;
+	self->mem = MAP_FAILED;
+	self->aux = MAP_FAILED;
+	self->mem_len = 0;
+	self->swap_disabled = false;
+	self->swap_prio = -1;
+	self->swapcache_dropped = false;
+	self->swap_dev = NULL;
+
+	self->pmd_size = read_pmd_pagesize();
+	if (!self->pmd_size)
+		SKIP(return, "Cannot determine PMD size\n");
+
+	self->pagemap_fd = open("/proc/self/pagemap", O_RDONLY);
+	if (self->pagemap_fd < 0)
+		SKIP(return, "Cannot open /proc/self/pagemap\n");
+
+	if (!swap_available(self->pmd_size))
+		SKIP(return, "No active swap device has enough free space\n");
+
+	self->seed = random_seed();
+	self->zswap_enabled = zswap_enabled();
+	self->mem = alloc_fill_swap_thp(self->pmd_size, self->pagemap_fd,
+					self->seed, &swap_failed);
+	if (self->mem == MAP_FAILED) {
+		ASSERT_FALSE(swap_failed);
+		SKIP(return, "Could not create swapped THP\n");
+	}
+	self->mem_len = self->pmd_size;
+	self->swapcache_dropped = drop_swapcache(self->mem, self->pmd_size);
+	ksft_print_msg("swap cache %s the swapped-out THP\n",
+		       self->swapcache_dropped ? "no longer holds"
+					       : "still holds");
+}
+
+FIXTURE_TEARDOWN(pmd_swap)
+{
+	int swap_err = 0;
+	int swap_ret = 0;
+
+	if (self->swap_disabled) {
+		swap_ret = swapon_restore(self->swap_dev, self->swap_prio);
+		swap_err = errno;
+	}
+	if (self->uffd >= 0)
+		close(self->uffd);
+	if (self->aux != MAP_FAILED)
+		munmap(self->aux, self->pmd_size);
+	if (self->mem != MAP_FAILED)
+		munmap(self->mem, self->mem_len);
+	if (self->pagemap_fd >= 0)
+		close(self->pagemap_fd);
+
+	EXPECT_EQ(swap_ret, 0) {
+		TH_LOG("swapon(%s) failed: %s", self->swap_dev,
+		       strerror(swap_err));
+	}
+}
+
+TEST_F(pmd_swap, basic)
+{
+	ASSERT_TRUE(verify_pattern(self->mem, self->pmd_size, self->seed));
+}
+
+/*
+ * With the swap cache evicted, the fault cannot be served by remapping a
+ * cached folio, so this covers the PMD-order swapin_sync() read.
+ */
+TEST_F(pmd_swap, swapin_sync)
+{
+	if (!self->swapcache_dropped)
+		SKIP(return, "Could not evict the folio from the swap cache\n");
+
+	ASSERT_TRUE(verify_pattern(self->mem, self->pmd_size, self->seed));
+	if (self->zswap_enabled)
+		ksft_print_msg("zswap enabled: PMD restoration not checked\n");
+	else
+		ASSERT_TRUE(check_huge_anon(self->mem, self->pmd_size, 1,
+					    self->pmd_size));
+}
+
+TEST_F(pmd_swap, fork)
+{
+	pid_t pid;
+	int status;
+
+	pid = fork();
+	ASSERT_GE(pid, 0);
+
+	if (pid == 0)
+		_exit(verify_pattern(self->mem, self->pmd_size,
+				     self->seed) ? 0 : 1);
+
+	ASSERT_TRUE(verify_pattern(self->mem, self->pmd_size, self->seed));
+
+	ASSERT_EQ(waitpid(pid, &status, 0), pid);
+	ASSERT_TRUE(WIFEXITED(status));
+	ASSERT_EQ(WEXITSTATUS(status), 0);
+}
+
+TEST_F(pmd_swap, fork_cow)
+{
+	unsigned int parent_seed = self->seed;
+	unsigned int child_seed = ~self->seed;
+	unsigned int new_seed = self->seed ^ 0xa5a5a5a5;
+	int release_child[2];
+	bool parent_ok;
+	char c = 0;
+	pid_t pid;
+	int status, ret;
+
+	ASSERT_EQ(pipe(release_child), 0);
+
+	pid = fork();
+	ASSERT_GE(pid, 0);
+
+	if (pid == 0) {
+		close(release_child[1]);
+		if (read(release_child[0], &c, 1) != 1)
+			_exit(1);
+		if (!verify_pattern(self->mem, self->pmd_size, parent_seed))
+			_exit(2);
+		fill_pattern(self->mem, self->pmd_size, child_seed);
+		if (!verify_pattern(self->mem, self->pmd_size, child_seed))
+			_exit(3);
+		_exit(0);
+	}
+
+	close(release_child[0]);
+	fill_pattern(self->mem, self->pmd_size, new_seed);
+	parent_ok = verify_pattern(self->mem, self->pmd_size, new_seed);
+	ret = write(release_child[1], &c, 1);
+	close(release_child[1]);
+	ASSERT_EQ(waitpid(pid, &status, 0), pid);
+	ASSERT_EQ(ret, 1);
+	ASSERT_TRUE(parent_ok);
+	ASSERT_TRUE(WIFEXITED(status));
+	ASSERT_EQ(WEXITSTATUS(status), 0);
+	ASSERT_TRUE(verify_pattern(self->mem, self->pmd_size, new_seed));
+}
+
+TEST_F(pmd_swap, write)
+{
+	self->mem[0] = 0xbb;
+	ASSERT_EQ(self->mem[0], (char)0xbb);
+	ASSERT_TRUE(verify_pattern_range(self->mem + 1, self->pmd_size - 1,
+					 self->seed, 1));
+	if (self->zswap_enabled)
+		ksft_print_msg("zswap enabled: PMD restoration not checked\n");
+	else
+		ASSERT_TRUE(check_huge_anon(self->mem, self->pmd_size, 1,
+					    self->pmd_size));
+}
+
+TEST_F(pmd_swap, rwp_swapin)
+{
+	self->uffd = register_rwp(self->mem, self->pmd_size, true);
+	if (self->uffd < 0)
+		SKIP(return, "Userfaultfd RWP unsupported\n");
+
+	ASSERT_TRUE(expect_rwp_fault(self->uffd, self->mem, self->pmd_size,
+				     pattern_byte(self->seed, 0), false));
+	ASSERT_TRUE(verify_pattern(self->mem, self->pmd_size, self->seed));
+}
+
+TEST_F(pmd_swap, munmap)
+{
+	unsigned long swap_before, swap_after;
+	int ret;
+
+	swap_before = read_vmswap();
+	ASSERT_GE(swap_before, self->pmd_size);
+
+	ret = munmap(self->mem, self->pmd_size);
+	if (!ret) {
+		self->mem = MAP_FAILED;
+		self->mem_len = 0;
+	}
+	ASSERT_EQ(ret, 0);
+
+	swap_after = read_vmswap();
+	ASSERT_LE(swap_after, swap_before - self->pmd_size);
+}
+
+TEST_F(pmd_swap, mprotect)
+{
+	ASSERT_EQ(mprotect(self->mem, self->pmd_size, PROT_READ), 0);
+	ASSERT_TRUE(check_swapped(self->pagemap_fd, self->mem,
+				  self->pmd_size));
+	ASSERT_EQ(mprotect(self->mem, self->pmd_size,
+			   PROT_READ | PROT_WRITE), 0);
+	ASSERT_TRUE(check_swapped(self->pagemap_fd, self->mem,
+				  self->pmd_size));
+	ASSERT_TRUE(verify_pattern(self->mem, self->pmd_size, self->seed));
+}
+
+TEST_F(pmd_swap, split_mprotect)
+{
+	unsigned long half = self->pmd_size / 2;
+
+	ASSERT_EQ(mprotect(self->mem, half, PROT_READ), 0);
+	ASSERT_TRUE(check_swapped(self->pagemap_fd, self->mem,
+				  self->pmd_size));
+	ASSERT_EQ(mprotect(self->mem, half, PROT_READ | PROT_WRITE), 0);
+	ASSERT_TRUE(verify_pattern(self->mem, self->pmd_size, self->seed));
+}
+
+TEST_F(pmd_swap, split_munmap)
+{
+	unsigned long half = self->pmd_size / 2;
+	unsigned long swap_before = read_vmswap();
+	unsigned long i;
+	char *base = self->mem;
+	int ret;
+
+	ASSERT_GE(swap_before, half);
+	ret = munmap(base, half);
+	if (!ret) {
+		self->mem = base + half;
+		self->mem_len = half;
+	}
+	ASSERT_EQ(ret, 0);
+	ASSERT_LE(read_vmswap(), swap_before - half);
+
+	for (i = 0; i < half; i += getpagesize())
+		ASSERT_TRUE(pagemap_is_swapped(self->pagemap_fd,
+					       self->mem + i));
+	ASSERT_TRUE(verify_pattern_range(self->mem, half, self->seed, half));
+}
+
+TEST_F(pmd_swap, uffdio_move)
+{
+	struct uffdio_register reg = {};
+	struct uffdio_move move = {};
+	struct uffdio_api api = {};
+	bool rwp;
+
+	self->aux = mmap_pmd_aligned(self->pmd_size);
+	if (self->aux == MAP_FAILED)
+		SKIP(return, "Could not mmap aligned dst\n");
+	ASSERT_EQ(madvise(self->aux, self->pmd_size, MADV_HUGEPAGE), 0);
+
+	self->uffd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK);
+	if (self->uffd < 0)
+		SKIP(return, "userfaultfd unavailable\n");
+
+	api.api = UFFD_API;
+	api.features = UFFD_FEATURE_MOVE | UFFD_FEATURE_RWP;
+	if (ioctl(self->uffd, UFFDIO_API, &api) ||
+	    !(api.features & UFFD_FEATURE_MOVE))
+		SKIP(return, "UFFD_FEATURE_MOVE unsupported\n");
+	rwp = api.features & UFFD_FEATURE_RWP;
+
+	reg.range.start = (unsigned long)self->aux;
+	reg.range.len = self->pmd_size;
+	reg.mode = UFFDIO_REGISTER_MODE_MISSING |
+		   (rwp ? UFFDIO_REGISTER_MODE_RWP : 0);
+	ASSERT_EQ(ioctl(self->uffd, UFFDIO_REGISTER, &reg), 0);
+
+	move.dst = (unsigned long)self->aux;
+	move.src = (unsigned long)self->mem;
+	move.len = self->pmd_size;
+	ASSERT_EQ(ioctl(self->uffd, UFFDIO_MOVE, &move), 0);
+	ASSERT_EQ(move.move, self->pmd_size);
+
+	ASSERT_TRUE(check_swapped(self->pagemap_fd, self->aux,
+				  self->pmd_size));
+	if (rwp)
+		ASSERT_TRUE(expect_rwp_fault(self->uffd, self->aux,
+					     self->pmd_size,
+					     pattern_byte(self->seed, 0), false));
+	ASSERT_TRUE(verify_pattern(self->aux, self->pmd_size, self->seed));
+	if (self->zswap_enabled)
+		ksft_print_msg("zswap enabled: PMD restoration not checked\n");
+	else
+		ASSERT_TRUE(check_huge_anon(self->aux, self->pmd_size, 1,
+					    self->pmd_size));
+}
+
+TEST_F(pmd_swap, mremap)
+{
+	char *new_mem, *dst;
+
+	self->aux = mmap_pmd_aligned(self->pmd_size);
+	if (self->aux == MAP_FAILED)
+		SKIP(return, "Could not mmap aligned dst\n");
+	dst = self->aux;
+
+	new_mem = mremap(self->mem, self->pmd_size, self->pmd_size,
+			 MREMAP_MAYMOVE | MREMAP_FIXED, dst);
+	if (new_mem != MAP_FAILED) {
+		self->mem = new_mem;
+		self->aux = MAP_FAILED;
+	}
+	ASSERT_NE(new_mem, MAP_FAILED);
+	ASSERT_EQ(new_mem, dst);
+
+	ASSERT_TRUE(check_swapped(self->pagemap_fd, new_mem, self->pmd_size));
+	ASSERT_TRUE(verify_pattern(new_mem, self->pmd_size, self->seed));
+}
+
+TEST_F(pmd_swap, pagemap)
+{
+	uint64_t entry, first;
+	unsigned long off;
+
+	entry = pagemap_get_entry(self->pagemap_fd, self->mem);
+	ASSERT_TRUE(entry & (1ULL << 62));
+	ASSERT_FALSE(entry & (1ULL << 63));
+	first = entry & PM_PFRAME_MASK;
+
+	/*
+	 * The kernel zeroes the swap type/offset payload for readers without
+	 * CAP_SYS_ADMIN, so the slot-ordering check below would silently test
+	 * nothing. Skip instead of passing vacuously.
+	 */
+	if (!first)
+		SKIP(return, "pagemap swap offsets need CAP_SYS_ADMIN\n");
+
+	for (off = getpagesize(); off < self->pmd_size; off += getpagesize()) {
+		uint64_t idx = off / getpagesize();
+
+		entry = pagemap_get_entry(self->pagemap_fd, self->mem + off);
+		ASSERT_TRUE(entry & (1ULL << 62));
+		ASSERT_FALSE(entry & (1ULL << 63));
+		ASSERT_EQ(entry & PM_PFRAME_MASK,
+			  first + (idx << MAX_SWAPFILES_SHIFT));
+	}
+}
+
+TEST_F(pmd_swap, mincore)
+{
+	unsigned long pages = self->pmd_size / getpagesize();
+	unsigned char vec[pages];
+	unsigned long i;
+
+	ASSERT_EQ(mincore(self->mem, self->pmd_size, vec), 0);
+	/*
+	 * Nothing in this test faults the range, and the fixture already
+	 * evicted the swap cache, so every slot must report not-resident. The
+	 * other direction is not stable - reclaim can drop the cached folio
+	 * between fixture setup and here, and a split cache reports per slot -
+	 * so only check that mincore() answered.
+	 */
+	if (self->swapcache_dropped) {
+		for (i = 0; i < pages; i++)
+			ASSERT_EQ(vec[i] & 1, 0);
+	}
+	ASSERT_TRUE(check_swapped(self->pagemap_fd, self->mem,
+				  self->pmd_size));
+}
+
+TEST_F(pmd_swap, madvise_free)
+{
+	unsigned long swap_before = read_vmswap();
+	unsigned long i;
+
+	ASSERT_TRUE(check_swapped(self->pagemap_fd, self->mem,
+				  self->pmd_size));
+	ASSERT_GE(swap_before, self->pmd_size);
+	ASSERT_EQ(madvise(self->mem, self->pmd_size, MADV_FREE), 0);
+	for (i = 0; i < self->pmd_size; i += getpagesize())
+		ASSERT_FALSE(pagemap_is_swapped(self->pagemap_fd,
+						self->mem + i));
+	ASSERT_LE(read_vmswap(), swap_before - self->pmd_size);
+	ASSERT_TRUE(verify_zero(self->mem, self->pmd_size));
+}
+
+TEST_F(pmd_swap, madvise_willneed)
+{
+	ASSERT_EQ(madvise(self->mem, self->pmd_size, MADV_WILLNEED), 0);
+	ASSERT_TRUE(check_swapped(self->pagemap_fd, self->mem,
+				  self->pmd_size));
+	ASSERT_TRUE(verify_pattern(self->mem, self->pmd_size, self->seed));
+	if (self->zswap_enabled)
+		ksft_print_msg("zswap enabled: PMD restoration not checked\n");
+	else
+		ASSERT_TRUE(check_huge_anon(self->mem, self->pmd_size, 1,
+					    self->pmd_size));
+}
+
+TEST_F(pmd_swap, swapoff)
+{
+	int ret, err;
+
+	self->swap_dev = getenv("PMD_SWAP_DEVICE");
+	if (!self->swap_dev)
+		SKIP(return, "PMD_SWAP_DEVICE env var not set\n");
+	/*
+	 * Otherwise a higher-priority device may have taken the PMD swap
+	 * entry and swapoff() would operate on the wrong backend.
+	 */
+	if (!swap_device_is_only_active(self->swap_dev, &self->swap_prio))
+		SKIP(return, "PMD_SWAP_DEVICE must be the only active swap device\n");
+
+	self->uffd = register_rwp(self->mem, self->pmd_size, true);
+
+	ret = swapoff(self->swap_dev);
+	err = errno;
+	if (!ret)
+		self->swap_disabled = true;
+	ASSERT_EQ(ret, 0) {
+		TH_LOG("swapoff(%s) failed: %s", self->swap_dev, strerror(err));
+	}
+
+	/*
+	 * Check residency before touching the memory. If we read
+	 * first, a bug that left a PMD swap entry in place after swapoff
+	 * would silently trigger do_huge_pmd_swap_page() and reinstall a
+	 * PMD mapping, masking the regression.
+	 */
+	if (self->zswap_enabled)
+		ksft_print_msg("zswap enabled: PMD restoration not checked\n");
+	else
+		ASSERT_TRUE(check_huge_anon(self->mem, self->pmd_size, 1,
+					    self->pmd_size));
+	if (self->uffd >= 0)
+		ASSERT_TRUE(expect_rwp_fault(self->uffd, self->mem,
+					     self->pmd_size,
+					     pattern_byte(self->seed, 0), false));
+	ASSERT_TRUE(verify_pattern(self->mem, self->pmd_size, self->seed));
+
+	ret = swapon_restore(self->swap_dev, self->swap_prio);
+	err = errno;
+	if (!ret)
+		self->swap_disabled = false;
+	ASSERT_EQ(ret, 0) {
+		TH_LOG("swapon(%s) failed: %s", self->swap_dev, strerror(err));
+	}
+}
+
+TEST_HARNESS_MAIN
diff --git a/tools/testing/selftests/mm/run_vmtests.sh b/tools/testing/selftests/mm/run_vmtests.sh
index 19755fb4edb94..720ba5cbacd62 100755
--- a/tools/testing/selftests/mm/run_vmtests.sh
+++ b/tools/testing/selftests/mm/run_vmtests.sh
@@ -69,6 +69,8 @@ separated by spaces:
 	test pagemap_scan IOCTL
 - pfnmap
 	tests for VM_PFNMAP handling
+- pmd_swap
+	tests for PMD-level swap entries
 - process_madv
 	test for process_madv
 - cow
@@ -414,6 +416,8 @@ CATEGORY="pagemap" run_test ./pagemap_ioctl
 
 CATEGORY="pfnmap" run_test ./pfnmap
 
+CATEGORY="pmd_swap" run_test ./pmd_swap
+
 # COW tests
 CATEGORY="cow" run_test ./cow
 
diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
index 80bc9f597b521..e6133784abad2 100644
--- a/tools/testing/selftests/mm/vm_util.c
+++ b/tools/testing/selftests/mm/vm_util.c
@@ -180,6 +180,30 @@ uint64_t read_pmd_pagesize(void)
 	return strtoul(buf, NULL, 10);
 }
 
+long read_vmstat(const char *name)
+{
+	char line[MAX_LINE_LENGTH];
+	size_t name_len = strlen(name);
+	long val = -1;
+	FILE *f;
+
+	f = fopen("/proc/vmstat", "r");
+	if (!f)
+		return -1;
+	/*
+	 * Match the whole field name: "thp_swpout" is a prefix of
+	 * "thp_swpout_fallback" and "thp_swpout_pmd".
+	 */
+	while (fgets(line, sizeof(line), f)) {
+		if (!strncmp(line, name, name_len) && line[name_len] == ' ') {
+			val = strtol(line + name_len + 1, NULL, 10);
+			break;
+		}
+	}
+	fclose(f);
+	return val;
+}
+
 unsigned long rss_anon(void)
 {
 	unsigned long rss_anon = 0;
diff --git a/tools/testing/selftests/mm/vm_util.h b/tools/testing/selftests/mm/vm_util.h
index 9a49af88702e4..6355d830cd4a8 100644
--- a/tools/testing/selftests/mm/vm_util.h
+++ b/tools/testing/selftests/mm/vm_util.h
@@ -89,6 +89,8 @@ unsigned long pagemap_get_pfn(int fd, char *start);
 void clear_softdirty(void);
 bool check_for_pattern(FILE *fp, const char *pattern, char *buf, size_t len);
 uint64_t read_pmd_pagesize(void);
+/* Returns the counter value, or -1 if /proc/vmstat has no such field. */
+long read_vmstat(const char *name);
 unsigned long rss_anon(void);
 bool check_huge_anon(void *addr, size_t len, int nr_hpages, uint64_t hpage_size);
 bool check_huge_file(void *addr, size_t len, int nr_hpages, uint64_t hpage_size);
-- 
2.53.0-Meta