Re: [PATCH net-next v3 3/5] net: gso: restore ids of outer ip headers correctly

[Richard Gobert <richardbgobert@gmail.com>]

Edward Cree wrote:
> On 21/08/2025 08:30, Richard Gobert wrote:
>> Currently, NETIF_F_TSO_MANGLEID indicates that the inner-most ID can
>> be mangled. Outer IDs can always be mangled.
>>
>> Make GSO preserve outer IDs by default, with NETIF_F_TSO_MANGLEID allowing
>> both inner and outer IDs to be mangled. In the future, we could add
>> NETIF_F_TSO_MANGLEID_INNER to provide more granular control to
>> drivers.
>>
>> This commit also modifies a few drivers that use SKB_GSO_FIXEDID directly.
>>
>> Signed-off-by: Richard Gobert <richardbgobert@gmail.com>
> ...
>> diff --git a/drivers/net/ethernet/sfc/ef100_tx.c b/drivers/net/ethernet/sfc/ef100_tx.c
>> index e6b6be549581..4efd22b44986 100644
>> --- a/drivers/net/ethernet/sfc/ef100_tx.c
>> +++ b/drivers/net/ethernet/sfc/ef100_tx.c
>> @@ -189,7 +189,8 @@ static void ef100_make_tso_desc(struct efx_nic *efx,
>>  {
>>  	bool gso_partial = skb_shinfo(skb)->gso_type & SKB_GSO_PARTIAL;
>>  	unsigned int len, ip_offset, tcp_offset, payload_segs;
>> -	u32 mangleid = ESE_GZ_TX_DESC_IP4_ID_INC_MOD16;
>> +	u32 mangleid_outer = ESE_GZ_TX_DESC_IP4_ID_INC_MOD16;
>> +	u32 mangleid_inner = ESE_GZ_TX_DESC_IP4_ID_INC_MOD16;
>>  	unsigned int outer_ip_offset, outer_l4_offset;
>>  	u16 vlan_tci = skb_vlan_tag_get(skb);
>>  	u32 mss = skb_shinfo(skb)->gso_size;
>> @@ -201,7 +202,9 @@ static void ef100_make_tso_desc(struct efx_nic *efx,
>>  	u32 paylen;
>>  
>>  	if (skb_shinfo(skb)->gso_type & SKB_GSO_TCP_FIXEDID)
>> -		mangleid = ESE_GZ_TX_DESC_IP4_ID_NO_OP;
>> +		mangleid_outer = ESE_GZ_TX_DESC_IP4_ID_NO_OP;
>> +	if (skb_shinfo(skb)->gso_type & SKB_GSO_TCP_FIXEDID_INNER)
>> +		mangleid_inner = ESE_GZ_TX_DESC_IP4_ID_NO_OP;
>>  	if (efx->net_dev->features & NETIF_F_HW_VLAN_CTAG_TX)
>>  		vlan_enable = skb_vlan_tag_present(skb);
>>  
>> @@ -239,14 +242,13 @@ static void ef100_make_tso_desc(struct efx_nic *efx,
>>  			      ESF_GZ_TX_TSO_CSO_INNER_L4, 1,
>>  			      ESF_GZ_TX_TSO_INNER_L3_OFF_W, ip_offset >> 1,
>>  			      ESF_GZ_TX_TSO_INNER_L4_OFF_W, tcp_offset >> 1,
>> -			      ESF_GZ_TX_TSO_ED_INNER_IP4_ID, mangleid,
>> +			      ESF_GZ_TX_TSO_ED_INNER_IP4_ID, mangleid_inner,
>>  			      ESF_GZ_TX_TSO_ED_INNER_IP_LEN, 1,
>>  			      ESF_GZ_TX_TSO_OUTER_L3_OFF_W, outer_ip_offset >> 1,
>>  			      ESF_GZ_TX_TSO_OUTER_L4_OFF_W, outer_l4_offset >> 1,
>>  			      ESF_GZ_TX_TSO_ED_OUTER_UDP_LEN, udp_encap && !gso_partial,
>>  			      ESF_GZ_TX_TSO_ED_OUTER_IP_LEN, encap && !gso_partial,
>> -			      ESF_GZ_TX_TSO_ED_OUTER_IP4_ID, encap ? mangleid :
>> -								     ESE_GZ_TX_DESC_IP4_ID_NO_OP,
>> +			      ESF_GZ_TX_TSO_ED_OUTER_IP4_ID, mangleid_outer,
>>  			      ESF_GZ_TX_TSO_VLAN_INSERT_EN, vlan_enable,
>>  			      ESF_GZ_TX_TSO_VLAN_INSERT_TCI, vlan_tci
>>  		);
> 
> AFAICT this will now, in the case when FIXEDID isn't set, set
>  ESF_GZ_TX_TSO_ED_OUTER_IP4_ID on non-encapsulated frames, for which
>  ESF_GZ_TX_TSO_OUTER_L3_OFF_W has been set to 0.  I'm not 100% sure,
>  but I think that will cause the NIC to do an INC_MOD16 on octets 4
>  and 5 of the packet, corrupting the Ethernet header.
> Please retain the existing logic whereby ED_OUTER_IP4_ID is set to
>  NO_OP in the !encap case.
> Note that the EF100 host interface's semantics take the view that an
>  unencapsulated packet has an INNER and no OUTER header, which AIUI
>  is the opposite to how your new gso_type flags are defined, so I
>  think for !encap you also need to set mangleid_inner based on
>  SKB_GSO_TCP_FIXEDID, rather than SKB_GSO_TCP_FIXEDID_INNER.
> 
> My apologies for not spotting this in earlier versions.

Will fix this in v4. Thanks!