Re: [Intel-wired-lan] [PATCH] ixgbe: Use kmap_local_page in ixgbe_check_lbtest_frame()

[Eric Dumazet]

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.