netdev - Re: [PATCH] ixgbe: Don't call kmap() on page allocated with GFP

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Date:   Tue, 5 Jul 2022 11:21:59 -0700
From:   Ira Weiny <ira.weiny@...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>,
        Alexander Duyck <alexander.duyck@...il.com>
Subject: Re: [PATCH] ixgbe: Don't call kmap() on page allocated with
 GFP_ATOMIC

On Mon, Jul 04, 2022 at 04:01:29PM +0200, Fabio M. De Francesco wrote:
> Pages allocated with GFP_ATOMIC cannot come from Highmem. This is why
> there is no need to call kmap() on them.

I'm still not 100% sure where this page gets allocated but AFAICT it is
allocated in ixgbe_alloc_mapped_page() which calls dev_alloc_pages() for the
allocation which is where the GFP_ATOMIC is specified.

I think I would add this detail here.

That said, and assuming my analysis is correct, the code looks fine so:

Reviewed-by: Ira Weiny <ira.weiny@...el.com>

> 
> Therefore, don't call kmap() on rx_buffer->page() and instead use a
> plain page_address() to get the kernel address.
> 
> Suggested-by: Ira Weiny <ira.weiny@...el.com>
> Suggested-by: Alexander Duyck <alexander.duyck@...il.com>
> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@...il.com>
> ---
>  drivers/net/ethernet/intel/ixgbe/ixgbe_ethtool.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_ethtool.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_ethtool.c
> index 628d0eb0599f..71196fd92f81 100644
> --- a/drivers/net/ethernet/intel/ixgbe/ixgbe_ethtool.c
> +++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_ethtool.c
> @@ -1966,15 +1966,13 @@ 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 = page_address(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);
> -
>  	return match;
>  }
>  
> -- 
> 2.36.1
>