[PATCH v3 05/10] iov_iter: Create a function to prepare userspace VM for UBUF/IOVEC tests

[PATCH v3 05/10] iov_iter: Create a function to prepare userspace VM for UBUF/IOVEC tests

[David Howells]

Create a function to set up a userspace VM for the kunit testing thread and
set up a buffer within it such that ITER_UBUF and ITER_IOVEC tests can be
performed.

Note that this requires current->mm to point to a sufficiently set up
mm_struct.  This is done by partially mirroring what execve does.

The following steps are performed:

 (1) Allocate an mm_struct and pick an arch layout (required to set
     mm->get_unmapped_area).

 (2) Create an empty "stack" VMA so that the VMA maple tree is set up and
     won't cause a crash in the maple tree code later.  We don't actually
     care about the stack as we're not going to actually execute userspace.

 (3) Create an anon file and attach a bunch of folios to it so that the
     requested number of pages are accessible.

 (4) Make the kthread use the mm.  This must be done before mmap is called.

 (5) Shared-mmap the anon file into the allocated mm_struct.

This requires access to otherwise unexported core symbols: mm_alloc(),
vm_area_alloc(), insert_vm_struct() arch_pick_mmap_layout() and
anon_inode_getfile_secure(), which I've exported _GPL.

[?] Would it be better if this were done in core and not in a module?

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Andrew Morton <akpm@linux-foundation.org>
cc: Christoph Hellwig <hch@lst.de>
cc: Christian Brauner <brauner@kernel.org>
cc: Jens Axboe <axboe@kernel.dk>
cc: Al Viro <viro@zeniv.linux.org.uk>
cc: Matthew Wilcox <willy@infradead.org>
cc: David Hildenbrand <david@redhat.com>
cc: John Hubbard <jhubbard@nvidia.com>
cc: Brendan Higgins <brendanhiggins@google.com>
cc: David Gow <davidgow@google.com>
cc: Huacai Chen <chenhuacai@kernel.org>
cc: WANG Xuerui <kernel@xen0n.name>
cc: Heiko Carstens <hca@linux.ibm.com>
cc: Vasily Gorbik <gor@linux.ibm.com>
cc: Alexander Gordeev <agordeev@linux.ibm.com>
cc: Christian Borntraeger <borntraeger@linux.ibm.com>
cc: Sven Schnelle <svens@linux.ibm.com>
cc: linux-mm@kvack.org
cc: loongarch@lists.linux.dev
cc: linux-s390@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
cc: linux-kselftest@vger.kernel.org
cc: kunit-dev@googlegroups.com
---
 arch/s390/kernel/vdso.c |   1 +
 fs/anon_inodes.c        |   1 +
 kernel/fork.c           |   2 +
 lib/kunit_iov_iter.c    | 143 ++++++++++++++++++++++++++++++++++++++++
 mm/mmap.c               |   1 +
 mm/util.c               |   3 +
 6 files changed, 151 insertions(+)

diff --git a/arch/s390/kernel/vdso.c b/arch/s390/kernel/vdso.c
index bbaefd84f15e..6849eac59129 100644
--- a/arch/s390/kernel/vdso.c
+++ b/arch/s390/kernel/vdso.c
@@ -223,6 +223,7 @@ unsigned long vdso_size(void)
 		size += vdso64_end - vdso64_start;
 	return PAGE_ALIGN(size);
 }
+EXPORT_SYMBOL_GPL(vdso_size);
 
 int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 {
diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c
index d26222b7eefe..e4862dff235b 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 10917c3e1f03..f6d9e0d0685a 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..63e4dd1e7c1b 100644
--- a/lib/kunit_iov_iter.c
+++ b/lib/kunit_iov_iter.c
@@ -10,6 +10,13 @@
 #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/personality.h>
 #include <linux/uio.h>
 #include <linux/bvec.h>
 #include <kunit/test.h>
@@ -68,6 +75,20 @@ 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.
  */
@@ -151,6 +172,128 @@ static void iov_kunit_check_pattern(struct kunit *test, const u8 *buffer,
 	}
 }
 
+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;
+}
+
+/*
+ * Attach a userspace buffer to a kernel thread by adding an mm_struct to it
+ * and mmapping the buffer.  If the caller requires a list of pages for
+ * checking, then an anon_inode file is created, populated with pages and
+ * mmapped otherwise an anonymous mapping is used.
+ */
+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;
+
+	/*
+	 * If we want the pages, attach the pages to a file to prevent swap
+	 * interfering, otherwise use an anonymous mapping.
+	 */
+	if (ppages) {
+		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);
+	} else {
+		kthread_use_mm(mm);
+		buffer = (u8 __user *)vm_mmap(NULL, 0, PAGE_SIZE * npages,
+					      PROT_READ | PROT_WRITE,
+					      MAP_PRIVATE | MAP_ANONYMOUS, 0);
+	}
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, (void __force *)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 1971bfffcc03..8a2595b8ec59 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -3383,6 +3383,7 @@ 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 aa01f6ea5a75..518f7c085923 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -455,6 +455,9 @@ void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
 	mm->get_unmapped_area = arch_get_unmapped_area;
 }
 #endif
+#ifdef CONFIG_MMU
+EXPORT_SYMBOL_GPL(arch_pick_mmap_layout);
+#endif
 
 /**
  * __account_locked_vm - account locked pages to an mm's locked_vm

Re: [PATCH v3 05/10] iov_iter: Create a function to prepare userspace VM for UBUF/IOVEC tests

[Linus Torvalds]

On Wed, 15 Nov 2023 at 10:50, David Howells <dhowells@redhat.com> wrote:
>
> This requires access to otherwise unexported core symbols: mm_alloc(),
> vm_area_alloc(), insert_vm_struct() arch_pick_mmap_layout() and
> anon_inode_getfile_secure(), which I've exported _GPL.
>
> [?] Would it be better if this were done in core and not in a module?

I'm not going to take this, even if it were to be sent to me through Christian.

I think the exports really show that this shouldn't be done. And yes,
doing it in core would avoid the exports, but would be even worse.

Those functions exist for setting up user space. You should be doing
this in user space.

I'm getting really fed up with the problems that ther KUnit tests
cause. We have a long history of self-inflicted pain due to "unit
testing", where it has caused stupid problems like just overflowing
the kernel stack etc.

This needs to stop. And this is where I'm putting my foot down. No
more KUnit tests that make up interfaces - or use interfaces - that
they have absolutely no place using.

From a quick look, what you were doing was checking that the patterns
you set up in user space came through ok. Dammit, what's wrong with
just using read()/write() on a pipe, or splice, or whatever. It will
test exactly the same iov_iter thing.

Kernel code should do things that can *only* be done in the kernel.
This is not it.

              Linus

Re: [PATCH v3 05/10] iov_iter: Create a function to prepare userspace VM for UBUF/IOVEC tests

[David Howells]

Linus Torvalds <torvalds@linux-foundation.org> wrote:

> From a quick look, what you were doing was checking that the patterns
> you set up in user space came through ok. Dammit, what's wrong with
> just using read()/write() on a pipe, or splice, or whatever. It will
> test exactly the same iov_iter thing.

I was trying to make it possible to do these tests before starting userspace
as there's a good chance that if the UBUF/IOVEC iterators don't work right
then your system can't be booted.

Anyway, if I drop patches 5, 6, 7 and 10 (ie. the ones doing stuff with UBUF
and IOVEC-type iterators), would you be okay with the rest?

David

Re: [PATCH v3 05/10] iov_iter: Create a function to prepare userspace VM for UBUF/IOVEC tests

[Linus Torvalds]

On Wed, 15 Nov 2023 at 11:39, David Howells <dhowells@redhat.com> wrote:
>
> I was trying to make it possible to do these tests before starting userspace
> as there's a good chance that if the UBUF/IOVEC iterators don't work right
> then your system can't be booted.

Oh, I don't think that any unit test should bother to check for that
kind of catastrophic case.

If something is so broken that the kernel doesn't boot properly even
into some basic test infrastructure, then bisection will trivially
find where that breakage was introduced.

And if it's something as core as the iov iterators, it won't even get
past the initial developer unless it's some odd build system
interaction.

So extreme cases aren't even worth checking for. What's worth testing
is "the system boots and works, but I want to check the edge cases".

IOW, when it comes to things like user copies, it's things like
alignment, and the page fault edge cases with EFAULT in particular.
You can easily get the return value wrong for a user copy that ends up
with an unaligned fault at the end of the last mapped page. Everything
normal will still work fine, because nobody does something that odd.

But those are best handled as user mode tests.

           Linus

[PATCH v3 05/10] iov_iter: Create a function to prepare userspace VM for UBUF/IOVEC tests

[David Howells]

Create a function to set up a userspace VM for the kunit testing thread and
set up a buffer within it such that ITER_UBUF and ITER_IOVEC tests can be
performed.

Note that this requires current->mm to point to a sufficiently set up
mm_struct.  This is done by partially mirroring what execve does.

The following steps are performed:

 (1) Allocate an mm_struct and pick an arch layout (required to set
     mm->get_unmapped_area).

 (2) Create an empty "stack" VMA so that the VMA maple tree is set up and
     won't cause a crash in the maple tree code later.  We don't actually
     care about the stack as we're not going to actually execute userspace.

 (3) Create an anon file and attach a bunch of folios to it so that the
     requested number of pages are accessible.

 (4) Make the kthread use the mm.  This must be done before mmap is called.

 (5) Shared-mmap the anon file into the allocated mm_struct.

This requires access to otherwise unexported core symbols: mm_alloc(),
vm_area_alloc(), insert_vm_struct() arch_pick_mmap_layout() and
anon_inode_getfile_secure(), which I've exported _GPL.

[?] Would it be better if this were done in core and not in a module?

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Andrew Morton <akpm@linux-foundation.org>
cc: Christoph Hellwig <hch@lst.de>
cc: Christian Brauner <brauner@kernel.org>
cc: Jens Axboe <axboe@kernel.dk>
cc: Al Viro <viro@zeniv.linux.org.uk>
cc: Matthew Wilcox <willy@infradead.org>
cc: David Hildenbrand <david@redhat.com>
cc: John Hubbard <jhubbard@nvidia.com>
cc: Brendan Higgins <brendanhiggins@google.com>
cc: David Gow <davidgow@google.com>
cc: Huacai Chen <chenhuacai@kernel.org>
cc: WANG Xuerui <kernel@xen0n.name>
cc: Heiko Carstens <hca@linux.ibm.com>
cc: Vasily Gorbik <gor@linux.ibm.com>
cc: Alexander Gordeev <agordeev@linux.ibm.com>
cc: Christian Borntraeger <borntraeger@linux.ibm.com>
cc: Sven Schnelle <svens@linux.ibm.com>
cc: linux-mm@kvack.org
cc: loongarch@lists.linux.dev
cc: linux-s390@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
cc: linux-kselftest@vger.kernel.org
cc: kunit-dev@googlegroups.com
---
 arch/s390/kernel/vdso.c |   1 +
 fs/anon_inodes.c        |   1 +
 kernel/fork.c           |   2 +
 lib/kunit_iov_iter.c    | 143 ++++++++++++++++++++++++++++++++++++++++
 mm/mmap.c               |   1 +
 mm/util.c               |   3 +
 6 files changed, 151 insertions(+)

diff --git a/arch/s390/kernel/vdso.c b/arch/s390/kernel/vdso.c
index bbaefd84f15e..6849eac59129 100644
--- a/arch/s390/kernel/vdso.c
+++ b/arch/s390/kernel/vdso.c
@@ -223,6 +223,7 @@ unsigned long vdso_size(void)
 		size += vdso64_end - vdso64_start;
 	return PAGE_ALIGN(size);
 }
+EXPORT_SYMBOL_GPL(vdso_size);
 
 int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 {
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..63e4dd1e7c1b 100644
--- a/lib/kunit_iov_iter.c
+++ b/lib/kunit_iov_iter.c
@@ -10,6 +10,13 @@
 #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/personality.h>
 #include <linux/uio.h>
 #include <linux/bvec.h>
 #include <kunit/test.h>
@@ -68,6 +75,20 @@ 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.
  */
@@ -151,6 +172,128 @@ static void iov_kunit_check_pattern(struct kunit *test, const u8 *buffer,
 	}
 }
 
+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;
+}
+
+/*
+ * Attach a userspace buffer to a kernel thread by adding an mm_struct to it
+ * and mmapping the buffer.  If the caller requires a list of pages for
+ * checking, then an anon_inode file is created, populated with pages and
+ * mmapped otherwise an anonymous mapping is used.
+ */
+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;
+
+	/*
+	 * If we want the pages, attach the pages to a file to prevent swap
+	 * interfering, otherwise use an anonymous mapping.
+	 */
+	if (ppages) {
+		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);
+	} else {
+		kthread_use_mm(mm);
+		buffer = (u8 __user *)vm_mmap(NULL, 0, PAGE_SIZE * npages,
+					      PROT_READ | PROT_WRITE,
+					      MAP_PRIVATE | MAP_ANONYMOUS, 0);
+	}
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, (void __force *)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..09895358f067 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -455,6 +455,9 @@ void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
 	mm->get_unmapped_area = arch_get_unmapped_area;
 }
 #endif
+#ifdef CONFIG_MMU
+EXPORT_SYMBOL_GPL(arch_pick_mmap_layout);
+#endif
 
 /**
  * __account_locked_vm - account locked pages to an mm's locked_vm