linux-kernel - Re: [PATCH] intel: igb: igb_ethtool.c: Convert kmap() to kmap_local

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Date:   Fri, 15 Apr 2022 14:40:58 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     Alaa Mohamed <eng.alaamohamedsoliman.am@...il.com>
Cc:     outreachy@...ts.linux.dev, jesse.brandeburg@...el.com,
        anthony.l.nguyen@...el.com, davem@...emloft.net, kuba@...nel.org,
        pabeni@...hat.com, intel-wired-lan@...ts.osuosl.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] intel: igb: igb_ethtool.c: Convert kmap() to
 kmap_local_page()

On Fri, Apr 15, 2022 at 10:53:07PM +0200, Alaa Mohamed wrote:
> The use of kmap() is being deprecated in favor of kmap_local_page()
> where it is feasible.
> 
> With kmap_local_page(), the mapping is per thread, CPU local and not
> globally visible.
> 
> Signed-off-by: Alaa Mohamed <eng.alaamohamedsoliman.am@...il.com>
> ---
>  drivers/net/ethernet/intel/igb/igb_ethtool.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/igb/igb_ethtool.c b/drivers/net/ethernet/intel/igb/igb_ethtool.c
> index 2a5782063f4c..ba93aa4ae6a0 100644
> --- a/drivers/net/ethernet/intel/igb/igb_ethtool.c
> +++ b/drivers/net/ethernet/intel/igb/igb_ethtool.c
> @@ -1798,14 +1798,14 @@ static int igb_check_lbtest_frame(struct igb_rx_buffer *rx_buffer,
>  
>  	frame_size >>= 1;
>  
> -	data = kmap(rx_buffer->page);
> +	data = kmap_local_page(rx_buffer->page);
>  
>  	if (data[3] != 0xFF ||
>  	    data[frame_size + 10] != 0xBE ||
>  	    data[frame_size + 12] != 0xAF)
>  		match = false;
>  
> -	kunmap(rx_buffer->page);
> +	kunmap_local(rx_buffer->page);

kunmap_local() is different from kunmap().  It takes an address within the
mapped page.  From the kdoc:

/**
 * kunmap_local - Unmap a page mapped via kmap_local_page().
 * @__addr: An address within the page mapped
 *
 * @__addr can be any address within the mapped page.  Commonly it is the
 * address return from kmap_local_page(), but it can also include offsets.
 *
 * Unmapping should be done in the reverse order of the mapping.  See
 * kmap_local_page() for details.
 */
#define kunmap_local(__addr)                                    \
...


Ira

>  
>  	return match;
>  }
> -- 
> 2.35.2
>