Re: [PATCH v2] lib/test_bpf: Call page_address() on page acquired with GFP_KERNEL flag

Fabio M. De Francesco
2023-06-18T05:07:12Z

On martedì 13 giugno 2023 09:17:56 CEST Sumitra Sharma wrote:
> generate_test_data() acquires a page with alloc_page(GFP_KERNEL). Pages
> allocated with GFP_KERNEL cannot come from Highmem. This is why
> there is no need to call kmap() on them.
>
> Therefore, use a plain page_address() on that page.
>
> Suggested-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
> Signed-off-by: Sumitra Sharma <sumitraartsy@gmail.com>
> ---
>
> Changes in v2:
> - Remove the kmap() call and call page_address() instead.

NIT: Give credit to whom asked you for this removal and explain why the
mapping is not required.

> - Change the commit subject and message.
>
> lib/test_bpf.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/lib/test_bpf.c b/lib/test_bpf.c
> index ade9ac672adb..70fcd0bcf14b 100644
> --- a/lib/test_bpf.c
> +++ b/lib/test_bpf.c
> @@ -14388,11 +14388,10 @@ static void *generate_test_data(struct bpf_test
> *test, int sub) if (!page)
> goto err_kfree_skb;
>
> - ptr = kmap(page);
> + ptr = page_address(page);
> if (!ptr)
> goto err_free_page;

What is the reason of this test? Could "ptr" ever be NULL? What is the code
checking just few lines above this latter test?

Please, take a deeper look at this function as a whole.

Fabio

> memcpy(ptr, test->frag_data, MAX_DATA);
> - kunmap(page);
> skb_add_rx_frag(skb, 0, page, 0, MAX_DATA, MAX_DATA);
> }
>
> --
> 2.25.1