Subject: Re: [PATCH v14 6/8] lib/test: memcpy_kunit: add copy_page() and copy_mc_page() tests

From: Shuai Xue <[email-masked]>
Date: Wed, 27 May 2026 21:43:52 +0800

On 5/18/26 4:49 PM, Ruidong Tian wrote:
> Add KUnit tests for copy_page() and copy_mc_page(), modeled after
> the existing memcpy_test() style: a static page-aligned src and a
> two-page dst, filled with random bytes plus non-zero edges, then
> verify byte-for-byte equality and that the adjacent page is
> untouched. The copy_mc_page() case additionally checks the return
> value is 0 on clean memory and is gated on CONFIG_ARCH_HAS_COPY_MC.
> 
> Signed-off-by: Ruidong Tian <[email-masked]>
> ---
>   lib/tests/memcpy_kunit.c | 67 +++++++++++++++++++++++++++++++++++++++-
>   1 file changed, 66 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/tests/memcpy_kunit.c b/lib/tests/memcpy_kunit.c
> index d36933554e46..85df53ccfb0c 100644
> --- a/lib/tests/memcpy_kunit.c
> +++ b/lib/tests/memcpy_kunit.c
> @@ -493,6 +493,67 @@ static void memmove_overlap_test(struct kunit *test)
>   	}
>   }
>   
> +/* --- Page-sized copy tests --- */
> +
> +static u8 page_src[PAGE_SIZE] __aligned(PAGE_SIZE);
> +static u8 page_dst[PAGE_SIZE * 2] __aligned(PAGE_SIZE);
> +static const u8 page_zero[PAGE_SIZE] __aligned(PAGE_SIZE);
> +
> +static void init_page(struct kunit *test)
> +{
> +	/* Get many bit patterns. */
> +	get_random_bytes(page_src, PAGE_SIZE);
> +
> +	/* Make sure we have non-zero edges. */
> +	set_random_nonzero(test, &page_src[0]);
> +	set_random_nonzero(test, &page_src[PAGE_SIZE - 1]);
> +
> +	/* Explicitly zero the entire destination. */
> +	memset(page_dst, 0, ARRAY_SIZE(page_dst));

    init_page() memsets the entire two-page page_dst to zero, and the
    test then asserts the second page is still zero. A buggy copy_page()
    that overwrites the second page with bytes that happen to include a
    zero byte would still pass.

    Please fill page_dst with a non-zero sentinel (e.g. 0xA5) instead
    of zero, and check the second half against that sentinel using
    memchr_inv():

        memset(page_dst, 0xA5, ARRAY_SIZE(page_dst));
        ...
        KUNIT_ASSERT_TRUE_MSG(test,
            !memchr_inv(page_dst + PAGE_SIZE, 0xA5, PAGE_SIZE),
            "copy_page overflow into adjacent page");

    This also lets you delete page_zero[] entirely, which on
    PAGE_SIZE=64K configs (arm64) saves a non-trivial amount of BSS.

> +}
> +
> +static void copy_page_test(struct kunit *test)
> +{
> +	init_page(test);
> +
> +	/* Copy. */
> +	copy_page(page_dst, page_src);
> +
> +	/* Verify byte-for-byte exact. */
> +	KUNIT_ASSERT_EQ_MSG(test,
> +		memcmp(page_dst, page_src, PAGE_SIZE), 0,
> +		"copy_page content mismatch with random data");
> +
> +	/* Verify no overflow into second page. */
> +	KUNIT_ASSERT_EQ_MSG(test,
> +		memcmp(page_dst + PAGE_SIZE, page_zero, PAGE_SIZE), 0,
> +		"copy_page overflow into adjacent page");
> +}
> +
> +#ifdef CONFIG_ARCH_HAS_COPY_MC
> +static void copy_mc_page_test(struct kunit *test)
> +{
> +	int ret;
> +
> +	init_page(test);
> +
> +	/* Copy and check return value. */
> +	ret = copy_mc_page(page_dst, page_src);

 From sashiko:

Does this introduce a build regression on architectures like x86_64 or
powerpc?
The CONFIG_ARCH_HAS_COPY_MC flag is selected by multiple architectures,
but copy_mc_page() is an arm64-specific API. Other architectures use the
generic copy_mc_to_kernel() API instead.
If the kernel is built with KUnit enabled on non-arm64 architectures, it
appears copy_mc_page() would be an undeclared identifier.

Thanks.
Shuai