On Thu, 16 May 2019 11:13:47 -0700, Alexei Starovoitov wrote: > On Thu, May 16, 2019 at 10:57 AM Jakub Kicinski wrote: > > > > The preferred method of reporting the Layer 4 (TCP) checksum offload > > for packets decrypted by the device is to update the checksum field > > to the correct value for clear text and report CHECKSUM_UNNECESSARY > > or CHECKSUM_COMPLETE computed over clear text. However, the exact > > semantics of RX checksum offload when NIC performs data modification > > are not clear and subject to change. > > when host is consuming the tcp stream I don't see the value of > tcp checksum on top tls. > In that sense CHECKSUM_UNNECESSARY is fine and no > need to update checksum field. > Even in case of sockmap and tcp stream redirect it is still fine. > Only the tcp payload being redirected to a different tcp socket > and the headers are gone. > So imo in all cases CHECKSUM_UNNECESSARY is fine > even without adjustment to checksum field.
No question that CHECKSUM_UNNECESSARY currently works. But it's not "entirely" correct without the header fixup? Device modifies the data - it should fix up the checksum. I was trying (unsuccessfully) to hint at the fact that it's okay today to leave the checksum be, but at the same time if someone is designing new HW or has the ability to fix this up in microcode I think the TCP csum should be fixed.. Maybe like this? The preferred method of reporting the Layer 4 (TCP) checksum offload for packets decrypted by the device is to update the checksum field to the correct value for clear text and report CHECKSUM_UNNECESSARY or CHECKSUM_COMPLETE computed over clear text. Some existing devices may report CHECKSUM_UNNECESSARY without fixing the checksum field, which currently functions correctly but is not in line with the exact semantics of RX checksum offload. Such devices must make sure that RXCSUM offload is always enabled for TLS offloaded flows. > Obviously the hw/firmware should have checked tcp csum before doing decrypt. Ah, that is definitely worth stating, will add!
