linux-kernel - [PATCH v4 3/6] kunit: test: Export kunit_attach

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Message-ID: <20250717011011.3365074-4-ynaffit@google.com>
Date: Wed, 16 Jul 2025 18:10:06 -0700
From: Tiffany Yang <ynaffit@...gle.com>
To: linux-kernel@...r.kernel.org
Cc: keescook@...gle.com, kernel-team@...roid.com, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	"Arve Hjønnevåg" <arve@...roid.com>, Todd Kjos <tkjos@...roid.com>, Martijn Coenen <maco@...roid.com>, 
	Joel Fernandes <joelagnelf@...dia.com>, Christian Brauner <brauner@...nel.org>, 
	Carlos Llamas <cmllamas@...gle.com>, Suren Baghdasaryan <surenb@...gle.com>, 
	Brendan Higgins <brendan.higgins@...ux.dev>, David Gow <davidgow@...gle.com>, 
	Rae Moar <rmoar@...gle.com>, linux-kselftest@...r.kernel.org, 
	kunit-dev@...glegroups.com, Kees Cook <kees@...nel.org>
Subject: [PATCH v4 3/6] kunit: test: Export kunit_attach_mm()

Tests can allocate from virtual memory using kunit_vm_mmap(), which
transparently creates and attaches an mm_struct to the test runner if
one is not already attached. This is suitable for most cases, except for
when the code under test must access a task's mm before performing an
mmap. Expose kunit_attach_mm() as part of the interface for those
cases. This does not change the existing behavior.

Cc: David Gow <davidgow@...gle.com>
Reviewed-by: Carlos Llamas <cmllamas@...gle.com>
Reviewed-by: Kees Cook <kees@...nel.org>
Signed-off-by: Tiffany Yang <ynaffit@...gle.com>
---
v4:
* Collected tags
---
 include/kunit/test.h   | 12 ++++++++++++
 lib/kunit/user_alloc.c |  4 ++--
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/include/kunit/test.h b/include/kunit/test.h
index 39c768f87dc9..d958ee53050e 100644
--- a/include/kunit/test.h
+++ b/include/kunit/test.h
@@ -531,6 +531,18 @@ static inline char *kunit_kstrdup(struct kunit *test, const char *str, gfp_t gfp
  */
 const char *kunit_kstrdup_const(struct kunit *test, const char *str, gfp_t gfp);
 
+/**
+ * kunit_attach_mm() - Create and attach a new mm if it doesn't already exist.
+ *
+ * Allocates a &struct mm_struct and attaches it to @current. In most cases, call
+ * kunit_vm_mmap() without calling kunit_attach_mm() directly. Only necessary when
+ * code under test accesses the mm before executing the mmap (e.g., to perform
+ * additional initialization beforehand).
+ *
+ * Return: 0 on success, -errno on failure.
+ */
+int kunit_attach_mm(void);
+
 /**
  * kunit_vm_mmap() - Allocate KUnit-tracked vm_mmap() area
  * @test: The test context object.
diff --git a/lib/kunit/user_alloc.c b/lib/kunit/user_alloc.c
index 46951be018be..b8cac765e620 100644
--- a/lib/kunit/user_alloc.c
+++ b/lib/kunit/user_alloc.c
@@ -22,8 +22,7 @@ struct kunit_vm_mmap_params {
 	unsigned long offset;
 };
 
-/* Create and attach a new mm if it doesn't already exist. */
-static int kunit_attach_mm(void)
+int kunit_attach_mm(void)
 {
 	struct mm_struct *mm;
 
@@ -49,6 +48,7 @@ static int kunit_attach_mm(void)
 
 	return 0;
 }
+EXPORT_SYMBOL_GPL(kunit_attach_mm);
 
 static int kunit_vm_mmap_init(struct kunit_resource *res, void *context)
 {
-- 
2.50.0.727.gbf7dc18ff4-goog