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

[Maciej Fijalkowski <maciej.fijalkowski@intel.com>]

On Thu, Jun 30, 2022 at 08:17:24AM -0700, Alexander Duyck wrote:
> On Thu, Jun 30, 2022 at 3:10 AM Maciej Fijalkowski
> <maciej.fijalkowski@intel.com> 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

I knew the second part but not the first, thanks.
So basically it is advised to convert the page_address() usage in similar
loopback testing code that other Intel drivers have, I'll do that later.

> 
> Thanks,
> 
> - Alex