In the kunit_iov_iter test prevent the kernel buffer from
being a single physically contiguous region.

Additionally, make sure that the test pattern written to
a page in the buffer depends on the offset of the page within
the buffer.

Cc: David Howells <dhowells@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Christian A. Ehrhardt <lk@c--e.de>
---
 lib/tests/kunit_iov_iter.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/lib/tests/kunit_iov_iter.c b/lib/tests/kunit_iov_iter.c
index bb847e5010eb..c42b9235f57a 100644
--- a/lib/tests/kunit_iov_iter.c
+++ b/lib/tests/kunit_iov_iter.c
@@ -13,6 +13,7 @@
 #include <linux/uio.h>
 #include <linux/bvec.h>
 #include <linux/folio_queue.h>
+#include <linux/minmax.h>
 #include <kunit/test.h>
 
 MODULE_DESCRIPTION("iov_iter testing");
@@ -37,7 +38,7 @@ static const struct kvec_test_range kvec_test_ranges[] = {
 
 static inline u8 pattern(unsigned long x)
 {
-	return x & 0xff;
+	return (u8)x + (u8)(x >> 8) + (u8)(x >> 16);
 }
 
 static void iov_kunit_unmap(void *data)
@@ -52,6 +53,7 @@ static void *__init iov_kunit_create_buffer(struct kunit *test,
 	struct page **pages;
 	unsigned long got;
 	void *buffer;
+	unsigned int i;
 
 	pages = kunit_kcalloc(test, npages, sizeof(struct page *), GFP_KERNEL);
         KUNIT_ASSERT_NOT_ERR_OR_NULL(test, pages);
@@ -62,6 +64,9 @@ static void *__init iov_kunit_create_buffer(struct kunit *test,
 		release_pages(pages, got);
 		KUNIT_ASSERT_EQ(test, got, npages);
 	}
+	/* Make sure that we don't get a physically contiguous buffer. */
+	for (i = 0; i < npages / 4; ++i)
+		swap(pages[i], pages[i + npages/2]);
 
 	buffer = vmap(pages, npages, VM_MAP | VM_MAP_PUT_PAGES, PAGE_KERNEL);
         KUNIT_ASSERT_NOT_ERR_OR_NULL(test, buffer);
-- 
2.43.0

On 24 March 2026 20:34:51 GMT, "Christian A. Ehrhardt" <lk@c--e.de> wrote:
>In the kunit_iov_iter test prevent the kernel buffer from
>being a single physically contiguous region.
>
>Additionally, make sure that the test pattern written to
>a page in the buffer depends on the offset of the page within
>the buffer.
>
>Cc: David Howells <dhowells@redhat.com>
>Cc: Andrew Morton <akpm@linux-foundation.org>
>Signed-off-by: Christian A. Ehrhardt <lk@c--e.de>
>---
> lib/tests/kunit_iov_iter.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
>diff --git a/lib/tests/kunit_iov_iter.c b/lib/tests/kunit_iov_iter.c
>index bb847e5010eb..c42b9235f57a 100644
>--- a/lib/tests/kunit_iov_iter.c
>+++ b/lib/tests/kunit_iov_iter.c
>@@ -13,6 +13,7 @@
> #include <linux/uio.h>
> #include <linux/bvec.h>
> #include <linux/folio_queue.h>
>+#include <linux/minmax.h>
> #include <kunit/test.h>
> MODULE_DESCRIPTION("iov_iter testing");
>@@ -37,7 +38,7 @@ static const struct kvec_test_range kvec_test_ranges[] = {
> 
> static inline u8 pattern(unsigned long x)
> {
>-	return x & 0xff;
>+	return (u8)x + (u8)(x >> 8) + (u8)(x >> 16);

Suggestion: You could use bitwise XOR if you like
return (x ^ (x >> 8) ^ (x >> 16)) & 0xff;


> }
> 
> static void iov_kunit_unmap(void *data)
>@@ -52,6 +53,7 @@ static void *__init iov_kunit_create_buffer(struct kunit *test,
> 	struct page **pages;
> 	unsigned long got;
> 	void *buffer;
>+	unsigned int i;

Nit: unsigned long is probably better here

> 
> 	pages = kunit_kcalloc(test, npages, sizeof(struct page *), GFP_KERNEL);
>         KUNIT_ASSERT_NOT_ERR_OR_NULL(test, pages);
>@@ -62,6 +64,9 @@ static void *__init iov_kunit_create_buffer(struct kunit *test,
> 		release_pages(pages, got);
> 		KUNIT_ASSERT_EQ(test, got, npages);
> 	}
>+	/* Make sure that we don't get a physically contiguous buffer. */
>+	for (i = 0; i < npages / 4; ++i)

I do really like this method, but

This may not be achievable, but if npages ever pass less than 4, it could evaluate to 0

>+		swap(pages[i], pages[i + npages/2]);

Nit: The spacing is a bit odd, you could change it to
swap(pages[i], pages[i + npages / 2]);

> 
> 	buffer = vmap(pages, npages, VM_MAP | VM_MAP_PUT_PAGES, PAGE_KERNEL);
>         KUNIT_ASSERT_NOT_ERR_OR_NULL(test, buffer);



This doesn't affect my reviewed by,  but just some things to clean up

V/R


Josh Law

Josh Law <objecting@objecting.org> wrote:

> >+	unsigned int i;
> 
> Nit: unsigned long is probably better here

Why?

> >+	for (i = 0; i < npages / 4; ++i)

I would suggest putting the type here:

	for (int i = 0; ...)

sort of thing.

David

On 24 March 2026 23:18:49 GMT, David Howells <dhowells@redhat.com> wrote:
>Josh Law <objecting@objecting.org> wrote:
>
>> >+	unsigned int i;
>> 
>> Nit: unsigned long is probably better here
>
>Why?
>
>> >+	for (i = 0; i < npages / 4; ++i)
>
>I would suggest putting the type here:
>
>	for (int i = 0; ...)
>
>sort of thing.
>
>David
>


Hmmm. You declare unsigned int i; but the total number of pages (npages) and the got counter are usually unsigned long in this context. But its a small nit, nothing that changes my opinion on this being merged :-)


V/R


Josh Law