From: "Toke Høiland-Jørgensen" <toke@redhat.com>
To: David Miller <davem@davemloft.net>
Cc: netdev@vger.kernel.org,
Jesper Dangaard Brouer <brouer@redhat.com>,
Daniel Borkmann <daniel@iogearbox.net>,
Alexei Starovoitov <ast@kernel.org>
Subject: Re: [PATCH net-next 2/2] devmap: Allow map lookups from eBPF
Date: Tue, 04 Jun 2019 22:22:47 +0200 [thread overview]
Message-ID: <871s09f6co.fsf@toke.dk> (raw)
In-Reply-To: <155966185078.9084.7775851923786129736.stgit@alrua-x1>
Toke Høiland-Jørgensen <toke@redhat.com> writes:
> We don't currently allow lookups into a devmap from eBPF, because the map
> lookup returns a pointer directly to the dev->ifindex, which shouldn't be
> modifiable from eBPF.
>
> However, being able to do lookups in devmaps is useful to know (e.g.)
> whether forwarding to a specific interface is enabled. Currently, programs
> work around this by keeping a shadow map of another type which indicates
> whether a map index is valid.
>
> To allow lookups, simply copy the ifindex into a scratch variable and
> return a pointer to this. If an eBPF program does modify it, this doesn't
> matter since it will be overridden on the next lookup anyway. While this
> does add a write to every lookup, the overhead of this is negligible
> because the cache line is hot when both the write and the subsequent read
> happens.
>
> Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
> ---
> kernel/bpf/devmap.c | 8 +++++++-
> kernel/bpf/verifier.c | 7 ++-----
> 2 files changed, 9 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
> index 5ae7cce5ef16..830650300ea4 100644
> --- a/kernel/bpf/devmap.c
> +++ b/kernel/bpf/devmap.c
> @@ -65,6 +65,7 @@ struct xdp_bulk_queue {
> struct bpf_dtab_netdev {
> struct net_device *dev; /* must be first member, due to tracepoint */
> struct bpf_dtab *dtab;
> + int ifindex_scratch;
Just realised I forgot to make this per-cpu; I'll send an updated
version once we settle on a solution that works for xskmap as well...
-Toke
prev parent reply other threads:[~2019-06-04 20:22 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-04 15:24 [PATCH net-next 0/2] xdp: Allow lookup into devmaps before redirect Toke Høiland-Jørgensen
2019-06-04 15:24 ` [PATCH net-next 1/2] bpf_xdp_redirect_map: Add flag to return XDP_PASS on map lookup failure Toke Høiland-Jørgensen
2019-06-05 10:39 ` Jesper Dangaard Brouer
2019-06-05 15:09 ` Jonathan Lemon
2019-06-06 10:01 ` Toke Høiland-Jørgensen
2019-06-04 15:24 ` [PATCH net-next 2/2] devmap: Allow map lookups from eBPF Toke Høiland-Jørgensen
2019-06-04 16:35 ` Jesper Dangaard Brouer
2019-06-04 18:42 ` Toke Høiland-Jørgensen
2019-06-04 19:41 ` Jonathan Lemon
2019-06-04 20:00 ` Toke Høiland-Jørgensen
2019-06-04 20:22 ` Toke Høiland-Jørgensen [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=871s09f6co.fsf@toke.dk \
--to=toke@redhat.com \
--cc=ast@kernel.org \
--cc=brouer@redhat.com \
--cc=daniel@iogearbox.net \
--cc=davem@davemloft.net \
--cc=netdev@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).