On Thu, Jul 29, 2021 at 12:39:48PM +0300, Gregory Etelson wrote:

csumonly engine calculates TX checksum of a tunnelled packet for outer
headers only or separately for outer and inner headers. The
calculation method is determined by checksum configuration options.
If TX checksum calculation is separated, the inner headers are
processed before outer headers.

Inner headers processing sets checksum values to 0 unconditionally.
If TX configuration offloads inner checksums only, outer checksum
calculation in software will read 0 instead of real values and
produce wrong result.

The patch zeroes inner checksums only before software calculation.

Fixes: 51f694dd40f5 ("app/testpmd: rework checksum forward engine")
Cc: stable@dpdk.org

As said previously, I think the correct Fixes line is:
Fixes: 6b520d54ebfe ("app/testpmd: use Tx preparation in checksum engine")

Acked-by: Olivier Matz <redacted>

Thanks