[PATCH RFC v2 4/4] KVM: selftests: exercise guest_memfd folio migration

[Shivank Garg]

Add a migration test to guest_memfd_test using guest_memfd files created
with MMAP, INIT_SHARED, and MIGRATABLE. MMAP and INIT_SHARED are required
here because move_pages() operates on userspace mapping. Run the test
only when the VM supports all three flags and the system has at least two
NUMA nodes (skipped otherwise).

Migrate every folio from node 0 to node 1 with move_pages(), and
verify both the resulting node and contents. Migrate the folios back
and verify their contents again.

Signed-off-by: Shivank Garg <shivankg@xxxxxxx>
---
 tools/testing/selftests/kvm/guest_memfd_test.c | 82 ++++++++++++++++++++++++++
 1 file changed, 82 insertions(+)

diff --git a/tools/testing/selftests/kvm/guest_memfd_test.c b/tools/testing/selftests/kvm/guest_memfd_test.c
index 2233d871a38f..77e034a9d587 100644
--- a/tools/testing/selftests/kvm/guest_memfd_test.c
+++ b/tools/testing/selftests/kvm/guest_memfd_test.c
@@ -171,6 +171,82 @@ static void test_numa_allocation(int fd, size_t total_size)
 	kvm_munmap(mem, total_size);
 }
 
+/*
+ * Each page is filled with a distinct byte (its index). Check every byte that
+ * data is intact after migration.
+ */
+static void verify_page(const char *page, int page_idx, size_t size,
+			const char *when)
+{
+	char expected = (char)(page_idx & 0xff);
+	size_t off;
+
+	for (off = 0; off < size; off++)
+		TEST_ASSERT(page[off] == expected,
+			    "Page %d corrupted at offset %zu %s", page_idx, off, when);
+}
+
+static void test_migrate_folio(int fd, size_t total_size)
+{
+	const unsigned long nodemask_0 = 1; /* nid: 0 */
+	unsigned long maxnode = BITS_PER_TYPE(nodemask_0);
+	int page_count = total_size / page_size;
+	int *status, *nodes;
+	void **addr;
+	char *mem;
+	int i;
+
+	if (!is_multi_numa_node_system())
+		return;
+
+	mem = kvm_mmap(total_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd);
+
+	addr = calloc(page_count, sizeof(*addr));
+	status = calloc(page_count, sizeof(*status));
+	nodes = calloc(page_count, sizeof(*nodes));
+	TEST_ASSERT(addr && status && nodes, "Failed to allocate page arrays");
+
+	/* Allocate all folios on node 0 and fill each with a known pattern. */
+	kvm_mbind(mem, total_size, MPOL_BIND, &nodemask_0, maxnode, 0);
+	for (i = 0; i < page_count; i++) {
+		memset(mem + i * page_size, (char)(i & 0xff), page_size);
+		addr[i] = mem + i * page_size;
+	}
+
+	kvm_move_pages(0, page_count, addr, NULL, status, 0);
+	for (i = 0; i < page_count; i++)
+		TEST_ASSERT(status[i] == 0, "Page %d should be on node 0", i);
+
+	/* Migrate node 0 -> 1, then check both the location and the data. */
+	for (i = 0; i < page_count; i++)
+		nodes[i] = 1;
+	kvm_move_pages(0, page_count, addr, nodes, status, MPOL_MF_MOVE);
+
+	kvm_move_pages(0, page_count, addr, NULL, status, 0);
+	for (i = 0; i < page_count; i++)
+		TEST_ASSERT(status[i] == 1,
+			    "Page %d should be on node 1 after migration", i);
+	for (i = 0; i < page_count; i++)
+		verify_page(mem + i * page_size, i, page_size, "after migration");
+
+	/* Migrate back node 1 -> 0, then re-check the location and the data. */
+	for (i = 0; i < page_count; i++)
+		nodes[i] = 0;
+	kvm_move_pages(0, page_count, addr, nodes, status, MPOL_MF_MOVE);
+
+	kvm_move_pages(0, page_count, addr, NULL, status, 0);
+	for (i = 0; i < page_count; i++)
+		TEST_ASSERT(status[i] == 0,
+			    "Page %d should be on node 0 after round-trip", i);
+	for (i = 0; i < page_count; i++)
+		verify_page(mem + i * page_size, i, page_size, "after round-trip");
+
+	free(addr);
+	free(status);
+	free(nodes);
+	kvm_munmap(mem, total_size);
+}
+
 static void test_collapse(int fd, u64 flags)
 {
 	const size_t pmd_size = get_trans_hugepagesz();
@@ -472,6 +548,9 @@ static void __test_guest_memfd(struct kvm_vm *vm, u64 flags)
 static void test_guest_memfd(unsigned long vm_type)
 {
 	struct kvm_vm *vm = vm_create_barebones_type(vm_type);
+	const u64 migrate_flags = GUEST_MEMFD_FLAG_MMAP |
+				  GUEST_MEMFD_FLAG_INIT_SHARED |
+				  GUEST_MEMFD_FLAG_MIGRATABLE;
 	u64 flags;
 
 	test_guest_memfd_flags(vm);
@@ -486,6 +565,9 @@ static void test_guest_memfd(unsigned long vm_type)
 	if (flags & GUEST_MEMFD_FLAG_INIT_SHARED)
 		__test_guest_memfd(vm, GUEST_MEMFD_FLAG_MMAP |
 				       GUEST_MEMFD_FLAG_INIT_SHARED);
+	/* Testing with move_pages() requires MMAP and INIT_SHARED. */
+	if ((flags & migrate_flags) == migrate_flags)
+		gmem_test(migrate_folio, vm, migrate_flags);
 
 	kvm_vm_free(vm);
 }

-- 
2.43.0