On Tue, Feb 28, 2017 at 3:22 PM, Eric Dumazet <eric.duma...@gmail.com> wrote: > On Tue, 2017-02-28 at 14:52 -0800, Andy Lutomirski wrote: > >> The user pages are a gift to the kernel. The application may not >> modify this memory ever, otherwise the page cache and on-disk data may >> differ. >> >> This is just not okay IMO. > > TCP works just fine in this case. > > TX checksum will be computed by the NIC after/while data is copied. > > If really the application changes the data, that will not cause any > problems, other than user side consistency. > > This is why we require a copy (for all buffers that came from zero-copy) > if network stack hits a device that can not offload TX checksum. > > Even pwrite() does not guarantee consistency if multiple threads are > using it on overlapping regions. > The Mellanox team working on TLS offload pointed out to us that if data is changed for a retransmit then it becomes trivial for someone snooping to break the encryption. Sounds pretty scary and it would be a shame if we couldn't use zero-copy in that use case :-( Hopefully we can find a solution...
Tom > >
