From: "Toke Høiland-Jørgensen" <toke@redhat.com>
To: Jonathan Lemon <jonathan.lemon@gmail.com>,
Jesper Dangaard Brouer <brouer@redhat.com>
Cc: netdev@vger.kernel.org, kernel-team@fb.com,
bjorn.topel@intel.com, magnus.karlsson@intel.com, ast@kernel.org,
daniel@iogearbox.net
Subject: Re: [PATCH v4 bpf-next 1/2] bpf: Allow bpf_map_lookup_elem() on an xskmap
Date: Tue, 04 Jun 2019 22:07:05 +0200 [thread overview]
Message-ID: <874l55f72u.fsf@toke.dk> (raw)
In-Reply-To: <87399C88-4388-4857-AD77-E98527DEFDA4@gmail.com>
Jonathan Lemon <jonathan.lemon@gmail.com> writes:
> On 4 Jun 2019, at 9:43, Jesper Dangaard Brouer wrote:
>
>> On Mon, 3 Jun 2019 09:38:51 -0700
>> Jonathan Lemon <jonathan.lemon@gmail.com> wrote:
>>
>>> Currently, the AF_XDP code uses a separate map in order to
>>> determine if an xsk is bound to a queue. Instead of doing this,
>>> have bpf_map_lookup_elem() return the queue_id, as a way of
>>> indicating that there is a valid entry at the map index.
>>
>> Just a reminder, that once we choose a return value, there the
>> queue_id, then it basically becomes UAPI, and we cannot change it.
>
> Yes - Alexei initially wanted to return the sk_cookie instead, but
> that's 64 bits and opens up a whole other can of worms.
>
>
>> Can we somehow use BTF to allow us to extend this later?
>>
>> I was also going to point out that, you cannot return a direct pointer
>> to queue_id, as BPF-prog side can modify this... but Daniel already
>> pointed this out.
>
> So, I see three solutions here (for this and Toke's patchset also,
> which is encountering the same problem).
>
> 1) add a scratch register (Toke's approach)
> 2) add a PTR_TO_<type>, which has the access checked. This is the most
> flexible approach, but does seem a bit overkill at the moment.
> 3) add another helper function, say, bpf_map_elem_present() which just
> returns a boolean value indicating whether there is a valid map entry
> or not.
>
> I was starting to do 2), but wanted to get some more feedback first.
I think I prefer 2) over 3); since we have a verifier that can actually
enforce something like read-only behaviour, actually having access to
the value will probably be useful to someone.
I can obviously live with 1) as well, of course (since I already did
that; though I just now realise that I forgot to make the scratch space
per-CPU)... :)
-Toke
next prev parent reply other threads:[~2019-06-04 20:07 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-03 16:38 [PATCH v4 bpf-next 0/2] Better handling of xskmap entries Jonathan Lemon
2019-06-03 16:38 ` [PATCH v4 bpf-next 1/2] bpf: Allow bpf_map_lookup_elem() on an xskmap Jonathan Lemon
2019-06-04 14:54 ` Daniel Borkmann
2019-06-04 15:30 ` Daniel Borkmann
2019-06-04 16:43 ` Jesper Dangaard Brouer
2019-06-04 17:25 ` Jonathan Lemon
2019-06-04 18:12 ` Martin Lau
2019-06-05 8:45 ` Björn Töpel
2019-06-05 15:42 ` Jonathan Lemon
2019-06-04 18:18 ` Björn Töpel
2019-06-04 20:07 ` Toke Høiland-Jørgensen [this message]
2019-06-03 16:38 ` [PATCH v4 bpf-next 2/2] libbpf: remove qidconf and better support external bpf programs Jonathan Lemon
2019-06-04 6:06 ` [PATCH v4 bpf-next 0/2] Better handling of xskmap entries Björn Töpel
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