linux-kernel - Re: [PATCH v4] lib/test_bpf: Call page_address() on page acquired with GFP

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Date:   Mon, 26 Jun 2023 15:07:22 +0200
From:   "Fabio M. De Francesco" <fmdefrancesco@...il.com>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
        Sumitra Sharma <sumitraartsy@...il.com>
Cc:     Ira Weiny <ira.weiny@...el.com>, Deepak R Varma <drv@...lo.com>,
        Sumitra Sharma <sumitraartsy@...il.com>
Subject: Re: [PATCH v4] lib/test_bpf: Call page_address() on page acquired with
 GFP_KERNEL flag

On venerdì 23 giugno 2023 17:16:44 CEST Sumitra Sharma wrote:
> generate_test_data() acquires a page with alloc_page(GFP_KERNEL).
> The GFP_KERNEL is typical for kernel-internal allocations.
> The caller requires ZONE_NORMAL or a lower zone for direct access.
> 
> Therefore the page cannot come from ZONE_HIGHMEM. Thus there's
> no need to map it with kmap().
> 
> Also, the kmap() is being deprecated in favor of kmap_local_page() [1].
> 
> Hence, use a plain page_address() directly.
> 
> Since the page passed to the page_address() is not from the highmem
> zone, the page_address() function will always return a valid kernel
> virtual address and will not return NULL. Hence, remove the check
> 'if (!ptr)'.
> 
> Remove the unused variable 'ptr' and label 'err_free_page'.
> 
> [1]: https://lore.kernel.org/all/20220813220034.806698-1-ira.weiny@intel.com/
> 
> Suggested-by: Fabio M. De Francesco <fmdefrancesco@...il.com>

I can't see no more things that prevent my tag, then it is...

Reviewed-by: Fabio M. De Francesco <fmdefrancesco@...il.com>

Thanks for working on it for all the time it took to get to v4 and for 
listening to what you've been suggested to change.

Well done :-)

Fabio

> Signed-off-by: Sumitra Sharma <sumitraartsy@...il.com>
> ---
> 
> - Link to v1:
> https://lore.kernel.org/bpf/20230613073020.GA359792@sumitra.com/T/ - Link to
> v2: https://lore.kernel.org/all/20230613071756.GA359746@sumitra.com/ - Link
> to v3: https://lore.kernel.org/all/20230622080729.GA426913@sumitra.com/
> 
> Changes in v4:
> Reported-by: kernel test robot <lkp@...el.com>
> Closes:
> https://lore.kernel.org/oe-kbuild-all/202306230559.hU5Aonpl-lkp@intel.com/ -
> Remove unused label 'err_free_page'.
> 
> Changes in v3:
> Noted by: Fabio M. De Francesco<fmdefrancesco@...il.com>
> 	- Remove the check 'if (!ptr)'.
> 	- Remove the unused variable 'ptr'.
> 	- Change the commit message.
> 
> Changes in v2:
> Noted by: Fabio M. De Francesco<fmdefrancesco@...il.com>
> 	- Remove the kmap() call and call page_address() instead.
> 	- Change the commit subject and message.
> 
>  lib/test_bpf.c | 10 +---------
>  1 file changed, 1 insertion(+), 9 deletions(-)
> 
> diff --git a/lib/test_bpf.c b/lib/test_bpf.c
> index ade9ac672adb..a5cc5f9fc4e8 100644
> --- a/lib/test_bpf.c
> +++ b/lib/test_bpf.c
> @@ -14381,25 +14381,17 @@ static void *generate_test_data(struct bpf_test
> *test, int sub) * single fragment to the skb, filled with
>  		 * test->frag_data.
>  		 */
> -		void *ptr;
> -
>  		page = alloc_page(GFP_KERNEL);
> 
>  		if (!page)
>  			goto err_kfree_skb;
> 
> -		ptr = kmap(page);
> -		if (!ptr)
> -			goto err_free_page;
> -		memcpy(ptr, test->frag_data, MAX_DATA);
> -		kunmap(page);
> +		memcpy(page_address(page), test->frag_data, MAX_DATA);
>  		skb_add_rx_frag(skb, 0, page, 0, MAX_DATA, MAX_DATA);
>  	}
> 
>  	return skb;
> 
> -err_free_page:
> -	__free_page(page);
>  err_kfree_skb:
>  	kfree_skb(skb);
>  	return NULL;
> --
> 2.25.1