linux-kernel - Re: [PATCH] ixgbe: Use kmap_local_page in ixgbe_check_lbtest

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Date:   Thu, 30 Jun 2022 12:10:22 +0200
From:   Maciej Fijalkowski <maciej.fijalkowski@...el.com>
To:     "Fabio M. De Francesco" <fmdefrancesco@...il.com>
Cc:     Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Tony Nguyen <anthony.l.nguyen@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        intel-wired-lan@...ts.osuosl.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
        Ira Weiny <ira.weiny@...el.com>, alexanderduyck@...com
Subject: Re: [PATCH] ixgbe: Use kmap_local_page in ixgbe_check_lbtest_frame()

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?

> 
> Suggested-by: Ira Weiny <ira.weiny@...el.com>
> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@...il.com>
> ---
>  drivers/net/ethernet/intel/ixgbe/ixgbe_ethtool.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_ethtool.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_ethtool.c
> index 628d0eb0599f..e64d40482bfd 100644
> --- a/drivers/net/ethernet/intel/ixgbe/ixgbe_ethtool.c
> +++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_ethtool.c
> @@ -1966,14 +1966,14 @@ static bool ixgbe_check_lbtest_frame(struct ixgbe_rx_buffer *rx_buffer,
>  
>  	frame_size >>= 1;
>  
> -	data = kmap(rx_buffer->page) + rx_buffer->page_offset;
> +	data = kmap_local_page(rx_buffer->page) + rx_buffer->page_offset;
>  
>  	if (data[3] != 0xFF ||
>  	    data[frame_size + 10] != 0xBE ||
>  	    data[frame_size + 12] != 0xAF)
>  		match = false;
>  
> -	kunmap(rx_buffer->page);
> +	kunmap_local(data);
>  
>  	return match;
>  }
> -- 
> 2.36.1
>