linux-kernel - Re: [net-next PATCH 05/11] net: ravb: Simplify types in RX csum validation

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Message-ID: <b4707880-2be4-4132-a3e1-8b104b89828c@omp.ru>
Date: Mon, 30 Sep 2024 22:11:17 +0300
From: Sergey Shtylyov <s.shtylyov@....ru>
To: Paul Barker <paul@...rker.dev>, "David S . Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo
 Abeni <pabeni@...hat.com>
CC: Paul Barker <paul.barker.ct@...renesas.com>, Geert Uytterhoeven
	<geert+renesas@...der.be>, Niklas Söderlund
	<niklas.soderlund+renesas@...natech.se>, Biju Das
	<biju.das.jz@...renesas.com>, Claudiu Beznea
	<claudiu.beznea.uj@...renesas.com>, <netdev@...r.kernel.org>,
	<linux-renesas-soc@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [net-next PATCH 05/11] net: ravb: Simplify types in RX csum
 validation

On 9/30/24 19:08, Paul Barker wrote:

> From: Paul Barker <paul.barker.ct@...renesas.com>
> 
> The HW checksum value is used as a 16-bit flag, it is zero when the

   I think I prefer s/HW/hardware/ but there's no hard feelings... :-)

> checksum has been validated and non-zero otherwise. Therefore we don't
> need to treat this as an actual __wsum type or call csum_unfold(), we
> can just use a u16 pointer.
> 
> Signed-off-by: Paul Barker <paul.barker.ct@...renesas.com>
[...]
> diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
> index 1dd2152734b0..9350ca10ab22 100644
> --- a/drivers/net/ethernet/renesas/ravb_main.c
> +++ b/drivers/net/ethernet/renesas/ravb_main.c
[...]
> @@ -762,23 +761,22 @@ static void ravb_rx_csum_gbeth(struct sk_buff *skb)
>  	 * The last 2 bytes are the protocol checksum status which will be zero
>  	 * if the checksum has been validated.
>  	 */
> -	if (unlikely(skb->len < sizeof(__sum16) * 2))
> +	csum_len = sizeof(*hw_csum) * 2;

   Could've been done by an initializer instead?

> +	if (unlikely(skb->len < csum_len))
>  		return;
>  
>  	if (skb_is_nonlinear(skb)) {
> -		last_frag = &shinfo->frags[shinfo->nr_frags - 1];
> -		hw_csum = skb_frag_address(last_frag) +
> -			  skb_frag_size(last_frag);
> -		skb_frag_size_sub(last_frag, 2 * sizeof(__sum16));
> +		skb_frag_t *last_frag = &shinfo->frags[shinfo->nr_frags - 1];

   Could've been done in the previous patch...

> +
> +		hw_csum = (u16 *)(skb_frag_address(last_frag) +
> +				  skb_frag_size(last_frag));
> +		skb_frag_size_sub(last_frag, csum_len);
>  	} else {
> -		hw_csum = skb_tail_pointer(skb);
> -		skb_trim(skb, skb->len - 2 * sizeof(__sum16));
> +		hw_csum = (u16 *)skb_tail_pointer(skb);
> +		skb_trim(skb, skb->len - csum_len);
>  	}
>  
> -	hw_csum -= sizeof(__sum16);
> -	csum_proto = csum_unfold((__force __sum16)get_unaligned_le16(hw_csum));
> -
> -	if (!csum_proto)
> +	if (!*--hw_csum)

   Hm, you lost get_unaligned_le16() here. The checksum can be anywhere,
unaligned too...

[...]

MBR, Sergey