On Sun, Jun 18, 2023 at 07:07:00AM +0200, Fabio M. De Francesco wrote: > 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@xxxxxxxxx> > > Signed-off-by: Sumitra Sharma <sumitraartsy@xxxxxxxxx> > > --- > > > > 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? > The code is allocating a page using alloc_page() with the GFP_KERNEL flag to obtain a kernel page frame. The checks if (!page) and if (!ptr) are verifying if the page allocation or the mapping operation were successful. If the pages obtained through page_address() are not from the highmem zone, the page_address() function will always return a valid kernel virtual address and will not return NULL. Hence, the check !ptr can be ignored while the !page must remain. I will be working on the v2 patch. I will also add the credits and add new lines to commit message explaining why the mapping is not required. Thank you for the help. Thanks & regards Sumitra > 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 > > > >
