lib/test_kho: use kho_preserve_vmalloc instead of storing addresses in fdt

KHO test stores physical addresses of the preserved folios directly in
fdt.  Use kho_preserve_vmalloc() instead of it and kho_restore_vmalloc()
to retrieve the addresses after kexec.

This makes the test more scalable from one side and adds tests coverage
for kho_preserve_vmalloc() from the other.

Link: https://lkml.kernel.org/r/20250921054458.4043761-5-rppt@kernel.org
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: Pratyush Yadav <pratyush@kernel.org>
Cc: Alexander Graf <graf@amazon.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Changyuan Lyu <changyuanl@google.com>
Cc: Chris Li <chrisl@kernel.org>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

lib/test_kho.c

@@ -32,6 +32,7 @@ module_param(max_mem, long, 0644);
 struct kho_test_state {
 	unsigned int nr_folios;
 	struct folio **folios;
+	phys_addr_t *folios_info;
 	struct folio *fdt;
 	__wsum csum;
 };
@@ -67,18 +68,15 @@ static struct notifier_block kho_test_nb = {
 
 static int kho_test_save_data(struct kho_test_state *state, void *fdt)
 {
-	phys_addr_t *folios_info;
+	phys_addr_t *folios_info __free(kvfree) = NULL;
+	struct kho_vmalloc folios_info_phys;
 	int err = 0;
 
-	err |= fdt_begin_node(fdt, "data");
+	folios_info = vmalloc_array(state->nr_folios, sizeof(*folios_info));
-	err |= fdt_property(fdt, "nr_folios", &state->nr_folios,
+	if (!folios_info)
-			    sizeof(state->nr_folios));
+		return -ENOMEM;
-	err |= fdt_property_placeholder(fdt, "folios_info",
-					state->nr_folios * sizeof(*folios_info),
-					(void **)&folios_info);
-	err |= fdt_property(fdt, "csum", &state->csum, sizeof(state->csum));
-	err |= fdt_end_node(fdt);
 
+	err = kho_preserve_vmalloc(folios_info, &folios_info_phys);
 	if (err)
 		return err;
 
@@ -93,6 +91,17 @@ static int kho_test_save_data(struct kho_test_state *state, void *fdt)
 			break;
 	}
 
+	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_phys,
+			    sizeof(folios_info_phys));
+	err |= fdt_property(fdt, "csum", &state->csum, sizeof(state->csum));
+	err |= fdt_end_node(fdt);
+
+	if (!err)
+		state->folios_info = no_free_ptr(folios_info);
+
 	return err;
 }
 
@@ -209,8 +218,9 @@ err_free_folios:
 
 static int kho_test_restore_data(const void *fdt, int node)
 {
+	const struct kho_vmalloc *folios_info_phys;
 	const unsigned int *nr_folios;
-	const phys_addr_t *folios_info;
+	phys_addr_t *folios_info;
 	const __wsum *old_csum;
 	__wsum csum = 0;
 	int len;
@@ -225,8 +235,12 @@ static int kho_test_restore_data(const void *fdt, int node)
 	if (!old_csum || len != sizeof(*old_csum))
 		return -EINVAL;
 
-	folios_info = fdt_getprop(fdt, node, "folios_info", &len);
+	folios_info_phys = fdt_getprop(fdt, node, "folios_info", &len);
-	if (!folios_info || len != sizeof(*folios_info) * *nr_folios)
+	if (!folios_info_phys || len != sizeof(*folios_info_phys))
+		return -EINVAL;
+
+	folios_info = kho_restore_vmalloc(folios_info_phys);
+	if (!folios_info)
 		return -EINVAL;
 
 	for (int i = 0; i < *nr_folios; i++) {
@@ -246,6 +260,8 @@ static int kho_test_restore_data(const void *fdt, int node)
 		folio_put(folio);
 	}
 
+	vfree(folios_info);
+
 	if (csum != *old_csum)
 		return -EINVAL;
 
@@ -304,6 +320,7 @@ static void kho_test_cleanup(void)
 		folio_put(kho_test_state.folios[i]);
 
 	kvfree(kho_test_state.folios);
+	vfree(kho_test_state.folios_info);
 	folio_put(kho_test_state.fdt);
 }