On Thu, Jun 30, 2022 at 11:18 AM Fabio M. De Francesco <fmdefrancesco@xxxxxxxxx> wrote: > > On giovedì 30 giugno 2022 18:09:18 CEST Alexander Duyck wrote: > > On Thu, Jun 30, 2022 at 8:25 AM Eric Dumazet <edumazet@xxxxxxxxxx> wrote: > > > > > > On Thu, Jun 30, 2022 at 5:17 PM Alexander Duyck > > > <alexander.duyck@xxxxxxxxx> wrote: > > > > > > > > On Thu, Jun 30, 2022 at 3:10 AM Maciej Fijalkowski > > > > <maciej.fijalkowski@xxxxxxxxx> wrote: > > > > > > > > > > On Wed, Jun 29, 2022 at 10:58:36AM +0200, Fabio M. De Francesco > wrote: > > > > > > The use of kmap() is being deprecated in favor of > kmap_local_page(). > > > > > > > > > > > > With kmap_local_page(), the mapping is per thread, CPU local and > not > > > > > > globally visible. Furthermore, the mapping can be acquired from > any context > > > > > > (including interrupts). > > > > > > > > > > > > Therefore, use kmap_local_page() in ixgbe_check_lbtest_frame() > because > > > > > > this mapping is per thread, CPU local, and not globally visible. > > > > > > > > > > Hi, > > > > > > > > > > I'd like to ask why kmap was there in the first place and not plain > > > > > page_address() ? > > > > > > > > > > Alex? > > > > > > > > The page_address function only works on architectures that have > access > > > > to all of physical memory via virtual memory addresses. The kmap > > > > function is meant to take care of highmem which will need to be > mapped > > > > before it can be accessed. > > > > > > > > For non-highmem pages kmap just calls the page_address function. > > > > https://elixir.bootlin.com/linux/latest/source/include/linux/highmem-internal.h#L40 > > > > > > > > > Sure, but drivers/net/ethernet/intel/ixgbe/ixgbe_main.c is allocating > > > pages that are not highmem ? > > > > > > This kmap() does not seem needed. > > > > Good point. So odds are page_address is fine to use. Actually there is > > a note to that effect in ixgbe_pull_tail. > > > > As such we could probably go through and update igb, and several of > > the other Intel drivers as well. > > > > - Alex > > > I don't know this code, however I know kmap*(). > > I assumed that, if author used kmap(), there was possibility that the page > came from highmem. > > In that case kmap_local_page() looks correct here. > > However, now I read that that page _cannot_ come from highmem. Therefore, > page_address() would suffice. > > If you all want I can replace kmap() / kunmap() with a "plain" > page_address(). Please let me know. > > Thanks, > > Fabio Replacing it with just page_address() should be fine. Back when I wrote the code I didn't realize that GFP_ATOMIC pages weren't allocated from highmem so I suspect I just used kmap since it was the way to cover all the bases. Thanks, - Alex
