kho: add test for kexec handover

Testing kexec handover requires a kernel driver that will generate some
data and preserve it with KHO on the first boot and then restore that data
and verify it was preserved properly after kexec.

To facilitate such test, along with the kernel driver responsible for data
generation, preservation and restoration add a script that runs a kernel
in a VM with a minimal /init.  The /init enables KHO, loads a kernel image
for kexec and runs kexec reboot.  After the boot of the kexeced kernel,
the driver verifies that the data was properly preserved.

[[email protected]: fix section mismatch]
  Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Mike Rapoport (Microsoft) <[email protected]>
Cc: Alexander Graf <[email protected]>
Cc: Changyuan Lyu <[email protected]>
Cc: Pasha Tatashin <[email protected]>
Cc: Pratyush Yadav <[email protected]>
Cc: Shuah Khan <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: rppt

MAINTAINERS

@@ -13353,6 +13353,7 @@ F:	Documentation/admin-guide/mm/kho.rst
 F:	Documentation/core-api/kho/*
 F:	include/linux/kexec_handover.h
 F:	kernel/kexec_handover.c
+F:	tools/testing/selftests/kho/
 
 KEYS-ENCRYPTED
 M:	Mimi Zohar <[email protected]>

lib/Kconfig.debug

@@ -3225,6 +3225,27 @@ config TEST_OBJPOOL
 
 	  If unsure, say N.
 
+config TEST_KEXEC_HANDOVER
+	bool "Test for Kexec HandOver"
+	default n
+	depends on KEXEC_HANDOVER
+	help
+	  This option enables test for Kexec HandOver (KHO).
+	  The test consists of two parts: saving kernel data before kexec and
+	  restoring the data after kexec and verifying that it was properly
+	  handed over. This test module creates and saves data on the boot of
+	  the first kernel and restores and verifies the data on the boot of
+	  kexec'ed kernel.
+
+	  For detailed documentation about KHO, see Documentation/core-api/kho.
+
+	  To run the test run:
+
+	  tools/testing/selftests/kho/vmtest.sh -h
+
+	  If unsure, say N.
+
+
 config INT_POW_KUNIT_TEST
 	tristate "Integer exponentiation (int_pow) test" if !KUNIT_ALL_TESTS
 	depends on KUNIT

lib/Makefile

@@ -102,6 +102,7 @@ obj-$(CONFIG_TEST_HMM) += test_hmm.o
 obj-$(CONFIG_TEST_FREE_PAGES) += test_free_pages.o
 obj-$(CONFIG_TEST_REF_TRACKER) += test_ref_tracker.o
 obj-$(CONFIG_TEST_OBJPOOL) += test_objpool.o
+obj-$(CONFIG_TEST_KEXEC_HANDOVER) += test_kho.o
 
 obj-$(CONFIG_TEST_FPU) += test_fpu.o
 test_fpu-y := test_fpu_glue.o test_fpu_impl.o

lib/test_kho.c

@@ -0,0 +1,305 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Test module for KHO
+ * Copyright (c) 2025 Microsoft Corporation.
+ *
+ * Authors:
+ *   Saurabh Sengar <[email protected]>
+ *   Mike Rapoport <[email protected]>
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/mm.h>
+#include <linux/gfp.h>
+#include <linux/slab.h>
+#include <linux/kexec.h>
+#include <linux/libfdt.h>
+#include <linux/module.h>
+#include <linux/printk.h>
+#include <linux/vmalloc.h>
+#include <linux/kexec_handover.h>
+
+#include <net/checksum.h>
+
+#define KHO_TEST_MAGIC	0x4b484f21	/* KHO! */
+#define KHO_TEST_FDT	"kho_test"
+#define KHO_TEST_COMPAT "kho-test-v1"
+
+static long max_mem = (PAGE_SIZE << MAX_PAGE_ORDER) * 2;
+module_param(max_mem, long, 0644);
+
+struct kho_test_state {
+	unsigned int nr_folios;
+	struct folio **folios;
+	struct folio *fdt;
+	__wsum csum;
+};
+
+static struct kho_test_state kho_test_state;
+
+static int kho_test_notifier(struct notifier_block *self, unsigned long cmd,
+			     void *v)
+{
+	struct kho_test_state *state = &kho_test_state;
+	struct kho_serialization *ser = v;
+	int err = 0;
+
+	switch (cmd) {
+	case KEXEC_KHO_ABORT:
+		return NOTIFY_DONE;
+	case KEXEC_KHO_FINALIZE:
+		/* Handled below */
+		break;
+	default:
+		return NOTIFY_BAD;
+	}
+
+	err |= kho_preserve_folio(state->fdt);
+	err |= kho_add_subtree(ser, KHO_TEST_FDT, folio_address(state->fdt));
+
+	return err ? NOTIFY_BAD : NOTIFY_DONE;
+}
+
+static struct notifier_block kho_test_nb = {
+	.notifier_call = kho_test_notifier,
+};
+
+static int kho_test_save_data(struct kho_test_state *state, void *fdt)
+{
+	phys_addr_t *folios_info __free(kvfree) = NULL;
+	int err = 0;
+
+	folios_info = kvmalloc_array(state->nr_folios, sizeof(*folios_info),
+				     GFP_KERNEL);
+	if (!folios_info)
+		return -ENOMEM;
+
+	for (int i = 0; i < state->nr_folios; i++) {
+		struct folio *folio = state->folios[i];
+		unsigned int order = folio_order(folio);
+
+		folios_info[i] = virt_to_phys(folio_address(folio)) | order;
+
+		err = kho_preserve_folio(folio);
+		if (err)
+			return err;
+	}
+
+	err |= fdt_begin_node(fdt, "data");
+	err |= fdt_property(fdt, "nr_folios", &state->nr_folios,
+			    sizeof(state->nr_folios));
+	err |= fdt_property(fdt, "folios_info", folios_info,
+			    state->nr_folios * sizeof(*folios_info));
+	err |= fdt_property(fdt, "csum", &state->csum, sizeof(state->csum));
+	err |= fdt_end_node(fdt);
+
+	return err;
+}
+
+static int kho_test_prepare_fdt(struct kho_test_state *state)
+{
+	const char compatible[] = KHO_TEST_COMPAT;
+	unsigned int magic = KHO_TEST_MAGIC;
+	ssize_t fdt_size;
+	int err = 0;
+	void *fdt;
+
+	fdt_size = state->nr_folios * sizeof(phys_addr_t) + PAGE_SIZE;
+	state->fdt = folio_alloc(GFP_KERNEL, get_order(fdt_size));
+	if (!state->fdt)
+		return -ENOMEM;
+
+	fdt = folio_address(state->fdt);
+
+	err |= fdt_create(fdt, fdt_size);
+	err |= fdt_finish_reservemap(fdt);
+
+	err |= fdt_begin_node(fdt, "");
+	err |= fdt_property(fdt, "compatible", compatible, sizeof(compatible));
+	err |= fdt_property(fdt, "magic", &magic, sizeof(magic));
+	err |= kho_test_save_data(state, fdt);
+	err |= fdt_end_node(fdt);
+
+	err |= fdt_finish(fdt);
+
+	if (err)
+		folio_put(state->fdt);
+
+	return err;
+}
+
+static int kho_test_generate_data(struct kho_test_state *state)
+{
+	size_t alloc_size = 0;
+	__wsum csum = 0;
+
+	while (alloc_size < max_mem) {
+		int order = get_random_u32() % NR_PAGE_ORDERS;
+		struct folio *folio;
+		unsigned int size;
+		void *addr;
+
+		/* cap allocation so that we won't exceed max_mem */
+		if (alloc_size + (PAGE_SIZE << order) > max_mem) {
+			order = get_order(max_mem - alloc_size);
+			if (order)
+				order--;
+		}
+		size = PAGE_SIZE << order;
+
+		folio = folio_alloc(GFP_KERNEL | __GFP_NORETRY, order);
+		if (!folio)
+			goto err_free_folios;
+
+		state->folios[state->nr_folios++] = folio;
+		addr = folio_address(folio);
+		get_random_bytes(addr, size);
+		csum = csum_partial(addr, size, csum);
+		alloc_size += size;
+	}
+
+	state->csum = csum;
+	return 0;
+
+err_free_folios:
+	for (int i = 0; i < state->nr_folios; i++)
+		folio_put(state->folios[i]);
+	return -ENOMEM;
+}
+
+static int kho_test_save(void)
+{
+	struct kho_test_state *state = &kho_test_state;
+	struct folio **folios __free(kvfree) = NULL;
+	unsigned long max_nr;
+	int err;
+
+	max_mem = PAGE_ALIGN(max_mem);
+	max_nr = max_mem >> PAGE_SHIFT;
+
+	folios = kvmalloc_array(max_nr, sizeof(*state->folios), GFP_KERNEL);
+	if (!folios)
+		return -ENOMEM;
+	state->folios = folios;
+
+	err = kho_test_generate_data(state);
+	if (err)
+		return err;
+
+	err = kho_test_prepare_fdt(state);
+	if (err)
+		return err;
+
+	return register_kho_notifier(&kho_test_nb);
+}
+
+static int kho_test_restore_data(const void *fdt, int node)
+{
+	const unsigned int *nr_folios;
+	const phys_addr_t *folios_info;
+	const __wsum *old_csum;
+	__wsum csum = 0;
+	int len;
+
+	node = fdt_path_offset(fdt, "/data");
+
+	nr_folios = fdt_getprop(fdt, node, "nr_folios", &len);
+	if (!nr_folios || len != sizeof(*nr_folios))
+		return -EINVAL;
+
+	old_csum = fdt_getprop(fdt, node, "csum", &len);
+	if (!old_csum || len != sizeof(*old_csum))
+		return -EINVAL;
+
+	folios_info = fdt_getprop(fdt, node, "folios_info", &len);
+	if (!folios_info || len != sizeof(*folios_info) * *nr_folios)
+		return -EINVAL;
+
+	for (int i = 0; i < *nr_folios; i++) {
+		unsigned int order = folios_info[i] & ~PAGE_MASK;
+		phys_addr_t phys = folios_info[i] & PAGE_MASK;
+		unsigned int size = PAGE_SIZE << order;
+		struct folio *folio;
+
+		folio = kho_restore_folio(phys);
+		if (!folio)
+			break;
+
+		if (folio_order(folio) != order)
+			break;
+
+		csum = csum_partial(folio_address(folio), size, csum);
+		folio_put(folio);
+	}
+
+	if (csum != *old_csum)
+		return -EINVAL;
+
+	return 0;
+}
+
+static int kho_test_restore(phys_addr_t fdt_phys)
+{
+	void *fdt = phys_to_virt(fdt_phys);
+	const unsigned int *magic;
+	int node, len, err;
+
+	node = fdt_path_offset(fdt, "/");
+	if (node < 0)
+		return -EINVAL;
+
+	if (fdt_node_check_compatible(fdt, node, KHO_TEST_COMPAT))
+		return -EINVAL;
+
+	magic = fdt_getprop(fdt, node, "magic", &len);
+	if (!magic || len != sizeof(*magic))
+		return -EINVAL;
+
+	if (*magic != KHO_TEST_MAGIC)
+		return -EINVAL;
+
+	err = kho_test_restore_data(fdt, node);
+	if (err)
+		return err;
+
+	pr_info("KHO restore succeeded\n");
+	return 0;
+}
+
+static int __init kho_test_init(void)
+{
+	phys_addr_t fdt_phys;
+	int err;
+
+	err = kho_retrieve_subtree(KHO_TEST_FDT, &fdt_phys);
+	if (!err)
+		return kho_test_restore(fdt_phys);
+
+	if (err != -ENOENT) {
+		pr_warn("failed to retrieve %s FDT: %d\n", KHO_TEST_FDT, err);
+		return err;
+	}
+
+	return kho_test_save();
+}
+module_init(kho_test_init);
+
+static void kho_test_cleanup(void)
+{
+	for (int i = 0; i < kho_test_state.nr_folios; i++)
+		folio_put(kho_test_state.folios[i]);
+
+	kvfree(kho_test_state.folios);
+}
+
+static void __exit kho_test_exit(void)
+{
+	unregister_kho_notifier(&kho_test_nb);
+	kho_test_cleanup();
+}
+module_exit(kho_test_exit);
+
+MODULE_AUTHOR("Mike Rapoport <[email protected]>");
+MODULE_DESCRIPTION("KHO test module");
+MODULE_LICENSE("GPL");

tools/testing/selftests/kho/arm64.conf

@@ -0,0 +1,9 @@
+QEMU_CMD="qemu-system-aarch64 -M virt -cpu max"
+QEMU_KCONFIG="
+CONFIG_SERIAL_AMBA_PL010=y
+CONFIG_SERIAL_AMBA_PL010_CONSOLE=y
+CONFIG_SERIAL_AMBA_PL011=y
+CONFIG_SERIAL_AMBA_PL011_CONSOLE=y
+"
+KERNEL_IMAGE="Image"
+KERNEL_CMDLINE="console=ttyAMA0"