Re: [net-next V8 PATCH 1/5] bpf: introduce new bpf cpu map type BPF_MAP_TYPE_CPUMAP

Jesper Dangaard Brouer
2017-10-17T10:47:41Z

On Mon, 16 Oct 2017 14:49:53 -0700
Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:

> On Mon, Oct 16, 2017 at 12:19:28PM +0200, Jesper Dangaard Brouer wrote:
> > The 'cpumap' is primarily used as a backend map for XDP BPF helper
> > call bpf_redirect_map() and XDP_REDIRECT action, like 'devmap'.
> >
> > This patch implement the main part of the map. It is not connected to
> > the XDP redirect system yet, and no SKB allocation are done yet.
> >
> > The main concern in this patch is to ensure the datapath can run
> > without any locking. This adds complexity to the setup and tear-down
> > procedure, which assumptions are extra carefully documented in the
> > code comments.
> >
> > V2:
> > - make sure array isn't larger than NR_CPUS
> > - make sure CPUs added is a valid possible CPU
> >
> > V3: fix nitpicks from Jakub Kicinski <kubakici@wp.pl>
> >
> > V5:
> > - Restrict map allocation to root / CAP_SYS_ADMIN
> > - WARN_ON_ONCE if queue is not empty on tear-down
> > - Return -EPERM on memlock limit instead of -ENOMEM
> > - Error code in __cpu_map_entry_alloc() also handle ptr_ring_cleanup()
> > - Moved cpu_map_enqueue() to next patch
> >
> > V6: all notice by Daniel Borkmann
> > - Fix err return code in cpu_map_alloc() introduced in V5
> > - Move cpu_possible() check after max_entries boundary check
> > - Forbid usage initially in check_map_func_compatibility()
> >
> > V7:
> > - Fix alloc error path spotted by Daniel Borkmann
> > - Did stress test adding+removing CPUs from the map concurrently
> > - Fixed refcnt issue on cpu_map_entry, kthread started too soon
> > - Make sure packets are flushed during tear-down, involved use of
> > rcu_barrier() and kthread_run only exit after queue is empty
> > - Fix alloc error path in __cpu_map_entry_alloc() for ptr_ring
> >
> > V8:
> > - Nitpicking comments and gramma by Edward Cree
> > - Fix missing semi-colon introduced in V7 due to rebasing
> > - Move struct bpf_cpu_map_entry members cpu+map_id to tracepoint patch
> >
> > Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
> > ---
> > include/linux/bpf_types.h | 1
> > include/uapi/linux/bpf.h | 1
> > kernel/bpf/Makefile | 1
> > kernel/bpf/cpumap.c | 560 ++++++++++++++++++++++++++++++++++++++++
> > kernel/bpf/syscall.c | 8 +
> > kernel/bpf/verifier.c | 5
> > tools/include/uapi/linux/bpf.h | 1
> > 7 files changed, 576 insertions(+), 1 deletion(-)
> > create mode 100644 kernel/bpf/cpumap.c
>
> Looks good to me
> I like the idea of running networking stack from kthread
> and hope adding GRO won't change the api.
> Acked-by: Alexei Starovoitov <ast@kernel.org>

Thanks!

I think adding GRO is still safe API-wise after this patchset. I
imagine that the GRO API will be tied to how we implement/expose the
RX-hash to the eBPF program. Thus, the API will be the eBPF prog can
change the RX-hash, to influence the GRO aggregation/partial-sort. If
the map need to behave differently for GRO then we have the map_flags
to adjust this behavior (but I assume this would not be needed).

--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
LinkedIn: http://www.linkedin.com/in/brouer