[RFC,5/9] iov_iter: Create a function to prepare userspace VM for UBUF/IOVEC tests

diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c
index 24192a7667ed..4190336180ee 100644
--- a/fs/anon_inodes.c
+++ b/fs/anon_inodes.c
@@ -176,6 +176,7 @@  struct file *anon_inode_getfile_secure(const char *name,
 	return __anon_inode_getfile(name, fops, priv, flags,
 				    context_inode, true);
 }
+EXPORT_SYMBOL_GPL(anon_inode_getfile_secure);
 
 static int __anon_inode_getfd(const char *name,
 			      const struct file_operations *fops,
diff --git a/kernel/fork.c b/kernel/fork.c
index 3b6d20dfb9a8..9ab604574400 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -494,6 +494,7 @@  struct vm_area_struct *vm_area_alloc(struct mm_struct *mm)
 
 	return vma;
 }
+EXPORT_SYMBOL_GPL(vm_area_alloc);
 
 struct vm_area_struct *vm_area_dup(struct vm_area_struct *orig)
 {
@@ -1337,6 +1338,7 @@  struct mm_struct *mm_alloc(void)
 	memset(mm, 0, sizeof(*mm));
 	return mm_init(mm, current, current_user_ns());
 }
+EXPORT_SYMBOL_GPL(mm_alloc);
 
 static inline void __mmput(struct mm_struct *mm)
 {
diff --git a/lib/kunit_iov_iter.c b/lib/kunit_iov_iter.c
index eb86371b67d0..3353bca9c40f 100644
--- a/lib/kunit_iov_iter.c
+++ b/lib/kunit_iov_iter.c
@@ -10,6 +10,12 @@ 
 #include <linux/module.h>
 #include <linux/vmalloc.h>
 #include <linux/mm.h>
+#include <linux/pagemap.h>
+#include <linux/mman.h>
+#include <linux/file.h>
+#include <linux/kthread.h>
+#include <linux/anon_inodes.h>
+#include <linux/writeback.h>
 #include <linux/uio.h>
 #include <linux/bvec.h>
 #include <kunit/test.h>
@@ -68,6 +74,20 @@  static void iov_kunit_unmap(void *data)
 	vunmap(data);
 }
 
+static void iov_kunit_mmdrop(void *data)
+{
+	struct mm_struct *mm = data;
+
+	if (current->mm == mm)
+		kthread_unuse_mm(mm);
+	mmdrop(mm);
+}
+
+static void iov_kunit_fput(void *data)
+{
+	fput(data);
+}
+
 /*
  * Create a buffer out of some pages and return a vmap'd pointer to it.
  */
@@ -96,6 +116,20 @@  static void *__init iov_kunit_create_buffer(struct kunit *test,
 	return buffer;
 }
 
+static void iov_kunit_fill_user_buf(struct kunit *test,
+				    u8 __user *buffer, size_t bufsize)
+{
+	size_t i;
+	int err;
+
+	for (i = 0; i < bufsize; i++) {
+		err = put_user(pattern(i), &buffer[i]);
+		KUNIT_EXPECT_EQ(test, err, 0);
+		if (test->status == KUNIT_FAILURE)
+			return;
+	}
+}
+
 /*
  * Build the reference pattern in the scratch buffer that we expect to see in
  * the iterator buffer (ie. the result of copy *to*).
@@ -151,6 +185,130 @@  static void iov_kunit_check_pattern(struct kunit *test, const u8 *buffer,
 	}
 }
 
+/*
+ * Compare a user and a scratch buffer to see that they're the same.
+ */
+static void iov_kunit_check_user_pattern(struct kunit *test, const u8 __user *buffer,
+					 const u8 *scratch, size_t bufsize)
+{
+	size_t i;
+	int err;
+	u8 c;
+
+	for (i = 0; i < bufsize; i++) {
+		err = get_user(c, &buffer[i]);
+		KUNIT_EXPECT_EQ(test, err, 0);
+		KUNIT_EXPECT_EQ_MSG(test, c, scratch[i], "at i=%x", i);
+		if (c != scratch[i])
+			return;
+	}
+}
+
+static const struct file_operations iov_kunit_user_file_fops = {
+	.mmap = generic_file_mmap,
+};
+
+static int iov_kunit_user_file_read_folio(struct file *file, struct folio *folio)
+{
+	folio_mark_uptodate(folio);
+	folio_unlock(folio);
+	return 0;
+}
+
+static const struct address_space_operations iov_kunit_user_file_aops = {
+	.read_folio	= iov_kunit_user_file_read_folio,
+	.dirty_folio	= filemap_dirty_folio,
+};
+
+/*
+ * Create an anonymous file and attach a bunch of pages to it.  We can then use
+ * this in mmap() and check the pages against it when doing extraction tests.
+ */
+static struct file *iov_kunit_create_file(struct kunit *test, size_t npages,
+					  struct page ***ppages)
+{
+	struct folio *folio;
+	struct file *file;
+	struct page **pages = NULL;
+	size_t i;
+
+	if (ppages) {
+		pages = kunit_kcalloc(test, npages, sizeof(struct page *), GFP_KERNEL);
+		KUNIT_ASSERT_NOT_ERR_OR_NULL(test, pages);
+		*ppages = pages;
+	}
+
+	file = anon_inode_getfile_secure("kunit-iov-test",
+					 &iov_kunit_user_file_fops,
+					 NULL, O_RDWR, NULL);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, file);
+	kunit_add_action_or_reset(test, iov_kunit_fput, file);
+	file->f_mapping->a_ops = &iov_kunit_user_file_aops;
+
+	i_size_write(file_inode(file), npages * PAGE_SIZE);
+	for (i = 0; i < npages; i++) {
+		folio = filemap_grab_folio(file->f_mapping, i);
+		KUNIT_ASSERT_NOT_ERR_OR_NULL(test, folio);
+		if (pages)
+			*pages++ = folio_page(folio, 0);
+		folio_unlock(folio);
+		folio_put(folio);
+	}
+
+	return file;
+}
+
+static u8 __user *__init iov_kunit_create_user_buf(struct kunit *test,
+						   size_t npages,
+						   struct page ***ppages)
+{
+	struct rlimit rlim_stack = {
+		.rlim_cur = LONG_MAX,
+		.rlim_max = LONG_MAX,
+	};
+	struct vm_area_struct *vma;
+	struct mm_struct *mm;
+	struct file *file;
+	u8 __user *buffer;
+	int ret;
+
+	KUNIT_ASSERT_NULL(test, current->mm);
+
+	mm = mm_alloc();
+	KUNIT_ASSERT_NOT_NULL(test, mm);
+	kunit_add_action_or_reset(test, iov_kunit_mmdrop, mm);
+	arch_pick_mmap_layout(mm, &rlim_stack);
+
+	vma = vm_area_alloc(mm);
+	KUNIT_ASSERT_NOT_NULL(test, vma);
+	vma_set_anonymous(vma);
+
+	/*
+	 * Place the stack at the largest stack address the architecture
+	 * supports. Later, we'll move this to an appropriate place. We don't
+	 * use STACK_TOP because that can depend on attributes which aren't
+	 * configured yet.
+	 */
+	vma->vm_end = STACK_TOP_MAX;
+	vma->vm_start = vma->vm_end - PAGE_SIZE;
+	vm_flags_init(vma, VM_SOFTDIRTY | VM_STACK_FLAGS | VM_STACK_INCOMPLETE_SETUP);
+	vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
+
+	ret = insert_vm_struct(mm, vma);
+	KUNIT_ASSERT_EQ(test, ret, 0);
+
+	mm->stack_vm = mm->total_vm = 1;
+
+	file = iov_kunit_create_file(test, npages, ppages);
+
+	kthread_use_mm(mm);
+	buffer = (u8 __user *)vm_mmap(file, 0, PAGE_SIZE * npages,
+				      PROT_READ | PROT_WRITE,
+				      MAP_SHARED, 0);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, buffer);
+	return buffer;
+}
+
 static void __init iov_kunit_load_kvec(struct kunit *test,
 				       struct iov_iter *iter, int dir,
 				       struct kvec *kvec, unsigned int kvmax,
diff --git a/mm/mmap.c b/mm/mmap.c
index b56a7f0c9f85..2ea4a98a2cab 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -3284,6 +3284,7 @@  int insert_vm_struct(struct mm_struct *mm, struct vm_area_struct *vma)
 
 	return 0;
 }
+EXPORT_SYMBOL_GPL(insert_vm_struct);
 
 /*
  * Copy the vma structure to a new location in the same mm,
diff --git a/mm/util.c b/mm/util.c
index 8cbbfd3a3d59..a393a308607c 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -455,6 +455,7 @@  void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
 	mm->get_unmapped_area = arch_get_unmapped_area;
 }
 #endif
+EXPORT_SYMBOL_GPL(arch_pick_mmap_layout);
 
 /**
  * __account_locked_vm - account locked pages to an mm's locked_vm