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

[Alex Elder <elder@linaro.org>]

On 3/4/21 11:26 PM, Bjorn Andersson wrote:
> On Thu 04 Mar 16:34 CST 2021, Alex Elder wrote:
> 
>> 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@linaro.org>
>> ---
>>   .../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..db76bbf000aa1 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 = be16_encode_bits(1, MAP_CSUM_UL_ENABLED_FMASK);
> 
> Why are you using be16_ here? Won't that cancel the htons() below?

Yes.  This was a mistake, and as you know, the kernel test
robot caught the problem with assigning a big endian value
to a host byte order variable.  This cannot have worked
before and I'm not sure what happened.

I've updated this series and am re-testing everything.  That
includes running the patches through sparse, but also includes
running with checksum offload enabled and verifying errors
are not reported when checksum offload active.

					-Alex

> Regards,
> Bjorn
> 
>>   	if (ip4h->protocol == IPPROTO_UDP)
>> -		ul_header->udp_ind = 1;
>> -	else
>> -		ul_header->udp_ind = 0;
>> +		val |= be16_encode_bits(1, MAP_CSUM_UL_UDP_FMASK);
>> +	val |= be16_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);
>>   
>>   	skb->ip_summed = CHECKSUM_NONE;
>>   
>> @@ -241,24 +237,19 @@ rmnet_map_ipv6_ul_csum_header(void *ip6hdr,
>>   			      struct rmnet_map_ul_csum_header *ul_header,
>>   			      struct sk_buff *skb)
>>   {
>> -	__be16 *hdr = (__be16 *)ul_header;
>>   	struct ipv6hdr *ip6h = ip6hdr;
>>   	u16 offset;
>> +	u16 val;
>>   
>>   	offset = skb_transport_header(skb) - (unsigned char *)ip6hdr;
>>   	ul_header->csum_start_offset = htons(offset);
>>   
>> -	ul_header->csum_insert_offset = skb->csum_offset;
>> -	ul_header->csum_enabled = 1;
>> -
>> +	val = be16_encode_bits(1, MAP_CSUM_UL_ENABLED_FMASK);
>>   	if (ip6h->nexthdr == IPPROTO_UDP)
>> -		ul_header->udp_ind = 1;
>> -	else
>> -		ul_header->udp_ind = 0;
>> +		val |= be16_encode_bits(1, MAP_CSUM_UL_UDP_FMASK);
>> +	val |= be16_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);
>>   
>>   	skb->ip_summed = CHECKSUM_NONE;
>>   
>> @@ -425,10 +416,7 @@ void rmnet_map_checksum_uplink_packet(struct sk_buff *skb,
>>   	}
>>   
>>   sw_csum:
>> -	ul_header->csum_start_offset = 0;
>> -	ul_header->csum_insert_offset = 0;
>> -	ul_header->csum_enabled = 0;
>> -	ul_header->udp_ind = 0;
>> +	memset(ul_header, 0, sizeof(*ul_header));
>>   
>>   	priv->stats.csum_sw++;
>>   }
>> diff --git a/include/linux/if_rmnet.h b/include/linux/if_rmnet.h
>> index 1fbb7531238b6..149d696feb520 100644
>> --- a/include/linux/if_rmnet.h
>> +++ b/include/linux/if_rmnet.h
>> @@ -33,17 +33,16 @@ struct rmnet_map_dl_csum_trailer {
>>   
>>   struct rmnet_map_ul_csum_header {
>>   	__be16 csum_start_offset;
>> -#if defined(__LITTLE_ENDIAN_BITFIELD)
>> -	u16 csum_insert_offset:14;
>> -	u16 udp_ind:1;
>> -	u16 csum_enabled:1;
>> -#elif defined (__BIG_ENDIAN_BITFIELD)
>> -	u16 csum_enabled:1;
>> -	u16 udp_ind:1;
>> -	u16 csum_insert_offset:14;
>> -#else
>> -#error	"Please fix <asm/byteorder.h>"
>> -#endif
>> +	__be16 csum_info;		/* MAP_CSUM_UL_*_FMASK */
>>   } __aligned(1);
>>   
>> +/* csum_info field:
>> + *  ENABLED:	1 = checksum computation requested
>> + *  UDP:	1 = UDP checksum (zero checkum means no checksum)
>> + *  OFFSET:	where (offset in bytes) to insert computed checksum
>> + */
>> +#define MAP_CSUM_UL_OFFSET_FMASK	GENMASK(13, 0)
>> +#define MAP_CSUM_UL_UDP_FMASK		GENMASK(14, 14)
>> +#define MAP_CSUM_UL_ENABLED_FMASK	GENMASK(15, 15)
>> +
>>   #endif /* !(_LINUX_IF_RMNET_H_) */
>> -- 
>> 2.20.1
>>