hw/net/cadence_gem: TX checksum offload does not work for fragmented packets

hw/net/cadence_gem: TX checksum offload does not work for fragmented packets

[Bin Meng]

Hi,

The cadence_gem does the TX checksum offload by:

                /* Is checksum offload enabled? */
                if (s->regs[GEM_DMACFG] & GEM_DMACFG_TXCSUM_OFFL) {
                    net_checksum_calculate(tx_packet, total_bytes);
                }

However this will only work for non-fragmented packets. For fragmented
packets, it just corrupts the packets by inserting wrong checksum to
the fist fragment, or corrupts the data to be sent in other fragments
than the first one.

Any idea of how to solve this cleanly?

Regards,
Bin

Re: hw/net/cadence_gem: TX checksum offload does not work for fragmented packets

[Bin Meng]

Hi Jason,

On Tue, Apr 21, 2020 at 10:31 PM Bin Meng <bmeng.cn@gmail.com> wrote:
>
> Hi,
>
> The cadence_gem does the TX checksum offload by:
>
>                 /* Is checksum offload enabled? */
>                 if (s->regs[GEM_DMACFG] & GEM_DMACFG_TXCSUM_OFFL) {
>                     net_checksum_calculate(tx_packet, total_bytes);
>                 }
>
> However this will only work for non-fragmented packets. For fragmented
> packets, it just corrupts the packets by inserting wrong checksum to
> the fist fragment, or corrupts the data to be sent in other fragments
> than the first one.
>
> Any idea of how to solve this cleanly?

I suspect this is a common issue for all NIC models in QEMU. Could you
please comment?

Regards,
Bin

Re: hw/net/cadence_gem: TX checksum offload does not work for fragmented packets

[Jason Wang]

On 2020/4/26 下午2:57, Bin Meng wrote:
> Hi Jason,
>
> On Tue, Apr 21, 2020 at 10:31 PM Bin Meng <bmeng.cn@gmail.com> wrote:
>> Hi,
>>
>> The cadence_gem does the TX checksum offload by:
>>
>>                  /* Is checksum offload enabled? */
>>                  if (s->regs[GEM_DMACFG] & GEM_DMACFG_TXCSUM_OFFL) {
>>                      net_checksum_calculate(tx_packet, total_bytes);
>>                  }
>>
>> However this will only work for non-fragmented packets. For fragmented
>> packets, it just corrupts the packets by inserting wrong checksum to
>> the fist fragment, or corrupts the data to be sent in other fragments
>> than the first one.
>>
>> Any idea of how to solve this cleanly?
> I suspect this is a common issue for all NIC models in QEMU. Could you
> please comment?
>
> Regards,
> Bin


I think maybe you can have a look at how it was done by e1000e which 
uses NetTxPkt structure. (E.g net_tx_pkt_update_ip_checksum()).

In the future, we may consider to convert the metadata that just uses 
NetTxPkt structure, but it's a non-trivial changes.

Thanks