ila: Fix checksum neutral mapping
The algorithm for checksum neutral mapping is incorrect. This problem was being hidden since we were previously always performing checksum offload on the translated addresses and only with IPv6 HW csum. Enabling an ILA router shows the issue. Corrected algorithm: old_loc is the original locator in the packet, new_loc is the value to overwrite with and is found in the lookup table. old_flag is the old flag value (zero of CSUM_NEUTRAL_FLAG) and new_flag is then (old_flag ^ CSUM_NEUTRAL_FLAG) & CSUM_NEUTRAL_FLAG. Need SUM(new_id + new_flag + diff) == SUM(old_id + old_flag) for checksum neutral translation. Solving for diff gives: diff = (old_id - new_id) + (old_flag - new_flag) compute_csum_diff8(new_id, old_id) gives old_id - new_id If old_flag is set old_flag - new_flag = old_flag = CSUM_NEUTRAL_FLAG Else old_flag - new_flag = -new_flag = ~CSUM_NEUTRAL_FLAG Tested: - Implemented a user space program that creates random addresses and random locators to overwrite. Compares the checksum over the address before and after translation (must always be equal) - Enabled ILA router and showed proper operation. Signed-off-by: NTom Herbert <tom@herbertland.com> Signed-off-by: NDavid S. Miller <davem@davemloft.net>
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