linux-kernel - RE: [PATCH net-next v2 6/6] net: qualcomm: rmnet: don't use C bit-fields in rmnet checksum header

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Date:   Mon, 8 Mar 2021 10:18:40 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Alex Elder' <elder@...aro.org>,
        "subashab@...eaurora.org" <subashab@...eaurora.org>,
        "stranche@...eaurora.org" <stranche@...eaurora.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>
CC:     "sharathv@...eaurora.org" <sharathv@...eaurora.org>,
        "bjorn.andersson@...aro.org" <bjorn.andersson@...aro.org>,
        "evgreen@...omium.org" <evgreen@...omium.org>,
        "cpratapa@...eaurora.org" <cpratapa@...eaurora.org>,
        "elder@...nel.org" <elder@...nel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kernel test robot" <lkp@...el.com>
Subject: RE: [PATCH net-next v2 6/6] net: qualcomm: rmnet: don't use C
 bit-fields in rmnet checksum header

From: Alex Elder
> Sent: 06 March 2021 03:16
> 
> Replace the use of C bit-fields in the rmnet_map_ul_csum_header
> structure with a single two-byte (big endian) structure member,
> and use field masks to encode or get values within it.
> 
> Previously rmnet_map_ipv4_ul_csum_header() would update values in
> the host byte-order fields, and then forcibly fix their byte order
> using a combination of byte order operations and types.
> 
> Instead, just compute the value that needs to go into the new
> structure member and save it with a simple byte-order conversion.
> 
> Make similar simplifications in rmnet_map_ipv6_ul_csum_header().
> 
> Finally, in rmnet_map_checksum_uplink_packet() a set of assignments
> zeroes every field in the upload checksum header.  Replace that with
> a single memset() operation.
> 
> Signed-off-by: Alex Elder <elder@...aro.org>
> Reported-by: kernel test robot <lkp@...el.com>
> ---
> v2: Fixed to use u16_encode_bits() instead of be16_encode_bits().
> 
>  .../ethernet/qualcomm/rmnet/rmnet_map_data.c  | 34 ++++++-------------
>  include/linux/if_rmnet.h                      | 21 ++++++------
>  2 files changed, 21 insertions(+), 34 deletions(-)
> 
> diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
> b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
> index 29d485b868a65..b76ad48da7325 100644
> --- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
> +++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
> @@ -198,23 +198,19 @@ rmnet_map_ipv4_ul_csum_header(void *iphdr,
>  			      struct rmnet_map_ul_csum_header *ul_header,
>  			      struct sk_buff *skb)
>  {
> -	__be16 *hdr = (__be16 *)ul_header;
>  	struct iphdr *ip4h = iphdr;
>  	u16 offset;
> +	u16 val;
> 
>  	offset = skb_transport_header(skb) - (unsigned char *)iphdr;
>  	ul_header->csum_start_offset = htons(offset);
> 
> -	ul_header->csum_insert_offset = skb->csum_offset;
> -	ul_header->csum_enabled = 1;
> +	val = u16_encode_bits(1, MAP_CSUM_UL_ENABLED_FMASK);
>  	if (ip4h->protocol == IPPROTO_UDP)
> -		ul_header->udp_ind = 1;
> -	else
> -		ul_header->udp_ind = 0;
> +		val |= u16_encode_bits(1, MAP_CSUM_UL_UDP_FMASK);
> +	val |= u16_encode_bits(skb->csum_offset, MAP_CSUM_UL_OFFSET_FMASK);
> 
> -	/* Changing remaining fields to network order */
> -	hdr++;
> -	*hdr = htons((__force u16)*hdr);
> +	ul_header->csum_info = htons(val);

Isn't this potentially misaligned?

	David

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