2023-06-22 08:03:03

by Sumitra Sharma

Subject: [PATCH v3] lib/test_bpf: Call page_address() on page acquired with GFP_KERNEL flag

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'.

[1]: https://lore.kernel.org/all/20220813220034.806698-1-ira.weiny
@intel.com/

Suggested-by: Fabio M. De Francesco <[email protected]>
Signed-off-by: Sumitra Sharma <[email protected]>
---

- Link to v1: https://lore.kernel.org/bpf/[email protected]/T/
- Link to v2: https://lore.kernel.org/lkml/3564297.R56niFO833@suse/T/

Changes in v3:
Noted by: Fabio M. De Francesco<[email protected]>
- Remove the check 'if (!ptr)'.
- Remove the unused variable 'ptr'.
- Change the commit message.

Changes in v2:
Noted by: Fabio M. De Francesco<[email protected]>
- Remove the kmap() call and call page_address() instead.
- Change the commit subject and message.


lib/test_bpf.c | 8 +-------
1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/lib/test_bpf.c b/lib/test_bpf.c
index ade9ac672adb..448bc1b0b8b5 100644
--- a/lib/test_bpf.c
+++ b/lib/test_bpf.c
@@ -14381,18 +14381,12 @@ 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);
}

--
2.25.1

2023-06-26 21:10:58

by Ira Weiny

Subject: Re: [PATCH v3] lib/test_bpf: Call page_address() on page acquired with GFP_KERNEL flag

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'.
>
> [1]: https://lore.kernel.org/all/20220813220034.806698-1-ira.weiny
> @intel.com/

Odd line break here which makes looking at this reference harder.

>
> Suggested-by: Fabio M. De Francesco <[email protected]>
> Signed-off-by: Sumitra Sharma <[email protected]>

The code looks good though.

Reviewed-by: Ira Weiny <[email protected]>

> ---
>
> - Link to v1: https://lore.kernel.org/bpf/[email protected]/T/
> - Link to v2: https://lore.kernel.org/lkml/3564297.R56niFO833@suse/T/
>
> Changes in v3:
> Noted by: Fabio M. De Francesco<[email protected]>
> - Remove the check 'if (!ptr)'.
> - Remove the unused variable 'ptr'.
> - Change the commit message.
>
> Changes in v2:
> Noted by: Fabio M. De Francesco<[email protected]>
> - Remove the kmap() call and call page_address() instead.
> - Change the commit subject and message.
>
>
> lib/test_bpf.c | 8 +-------
> 1 file changed, 1 insertion(+), 7 deletions(-)
>
> diff --git a/lib/test_bpf.c b/lib/test_bpf.c
> index ade9ac672adb..448bc1b0b8b5 100644
> --- a/lib/test_bpf.c
> +++ b/lib/test_bpf.c
> @@ -14381,18 +14381,12 @@ 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);
> }
>
> --
> 2.25.1
>