Re: [PATCH bpf-next 2/6] bpf, net: rework cookie generator as per-cpu one

On Fri, 25 Sep 2020 17:15:17 +0200 Eric Dumazet wrote:

On 9/25/20 5:00 PM, Jakub Kicinski wrote:

quoted

Is this_cpu_inc() in itself atomic?

To answer my own question - it is :)

quoted

                    unlikely((val & (COOKIE_LOCAL_BATCH - 1)) == 0))

Can we reasonably assume we won't have more than 4k CPUs and just
statically divide this space by encoding CPU id in top bits?  

This might give some food to side channel attacks, since this would
give an indication of cpu that allocated the id.

Also, I hear that some distros enabled 8K cpus.

Ok :(