From: "Toke Høiland-Jørgensen" <toke@redhat.com> To: Jesper Dangaard Brouer <jbrouer@redhat.com>, David Ahern <dsahern@gmail.com> Cc: John Fastabend <john.fastabend@gmail.com>, Daniel Borkmann <daniel@iogearbox.net>, Maciej Fijalkowski <maciej.fijalkowski@intel.com>, alardam@gmail.com, magnus.karlsson@intel.com, bjorn.topel@intel.com, andrii.nakryiko@gmail.com, kuba@kernel.org, ast@kernel.org, netdev@vger.kernel.org, davem@davemloft.net, hawk@kernel.org, jonathan.lemon@gmail.com, bpf@vger.kernel.org, jeffrey.t.kirsher@intel.com, maciejromanfijalkowski@gmail.com, intel-wired-lan@lists.osuosl.org, Marek Majtyka <marekx.majtyka@intel.com> Subject: Re: [PATCH v2 bpf 1/5] net: ethtool: add xdp properties flag set Date: Tue, 08 Dec 2020 12:58:55 +0100 [thread overview] Message-ID: <87lfe8ik5c.fsf@toke.dk> (raw) In-Reply-To: <20201208092803.05b27db3@carbon> Jesper Dangaard Brouer <jbrouer@redhat.com> writes: > On Mon, 7 Dec 2020 18:01:00 -0700 > David Ahern <dsahern@gmail.com> wrote: > >> On 12/7/20 1:52 PM, John Fastabend wrote: >> >> >> >> I think we need to keep XDP_TX action separate, because I think that >> >> there are use-cases where the we want to disable XDP_TX due to end-user >> >> policy or hardware limitations. >> > >> > How about we discover this at load time though. > > Nitpick at XDP "attach" time. The general disconnect between BPF and > XDP is that BPF can verify at "load" time (as kernel knows what it > support) while XDP can have different support/features per driver, and > cannot do this until attachment time. (See later issue with tail calls). > (All other BPF-hooks don't have this issue) > >> > Meaning if the program >> > doesn't use XDP_TX then the hardware can skip resource allocations for >> > it. I think we could have verifier or extra pass discover the use of >> > XDP_TX and then pass a bit down to driver to enable/disable TX caps. >> > >> >> This was discussed in the context of virtio_net some months back - it is >> hard to impossible to know a program will not return XDP_TX (e.g., value >> comes from a map). > > It is hard, and sometimes not possible. For maps the workaround is > that BPF-programmer adds a bound check on values from the map. If not > doing that the verifier have to assume all possible return codes are > used by BPF-prog. > > The real nemesis is program tail calls, that can be added dynamically > after the XDP program is attached. It is at attachment time that > changing the NIC resources is possible. So, for program tail calls the > verifier have to assume all possible return codes are used by BPF-prog. We actually had someone working on a scheme for how to express this for programs some months ago, but unfortunately that stalled out (Jesper already knows this, but FYI to the rest of you). In any case, I view this as a "next step". Just exposing the feature bits to userspace will help users today, and as a side effect, this also makes drivers declare what they support, which we can then incorporate into the core code to, e.g., reject attachment of programs that won't work anyway. But let's do this in increments and not make the perfect the enemy of the good here. > BPF now have function calls and function replace right(?) How does > this affect this detection of possible return codes? It does have the same issue as tail calls, in that the return code of the function being replaced can obviously change. However, the verifier knows the target of a replace, so it can propagate any constraints put upon the caller if we implement it that way. -Toke
WARNING: multiple messages have this Message-ID (diff)
From: Toke =?unknown-8bit?q?H=C3=B8iland-J=C3=B8rgensen?= <toke@redhat.com> To: intel-wired-lan@osuosl.org Subject: [Intel-wired-lan] [PATCH v2 bpf 1/5] net: ethtool: add xdp properties flag set Date: Tue, 08 Dec 2020 12:58:55 +0100 [thread overview] Message-ID: <87lfe8ik5c.fsf@toke.dk> (raw) In-Reply-To: <20201208092803.05b27db3@carbon> Jesper Dangaard Brouer <jbrouer@redhat.com> writes: > On Mon, 7 Dec 2020 18:01:00 -0700 > David Ahern <dsahern@gmail.com> wrote: > >> On 12/7/20 1:52 PM, John Fastabend wrote: >> >> >> >> I think we need to keep XDP_TX action separate, because I think that >> >> there are use-cases where the we want to disable XDP_TX due to end-user >> >> policy or hardware limitations. >> > >> > How about we discover this at load time though. > > Nitpick at XDP "attach" time. The general disconnect between BPF and > XDP is that BPF can verify at "load" time (as kernel knows what it > support) while XDP can have different support/features per driver, and > cannot do this until attachment time. (See later issue with tail calls). > (All other BPF-hooks don't have this issue) > >> > Meaning if the program >> > doesn't use XDP_TX then the hardware can skip resource allocations for >> > it. I think we could have verifier or extra pass discover the use of >> > XDP_TX and then pass a bit down to driver to enable/disable TX caps. >> > >> >> This was discussed in the context of virtio_net some months back - it is >> hard to impossible to know a program will not return XDP_TX (e.g., value >> comes from a map). > > It is hard, and sometimes not possible. For maps the workaround is > that BPF-programmer adds a bound check on values from the map. If not > doing that the verifier have to assume all possible return codes are > used by BPF-prog. > > The real nemesis is program tail calls, that can be added dynamically > after the XDP program is attached. It is at attachment time that > changing the NIC resources is possible. So, for program tail calls the > verifier have to assume all possible return codes are used by BPF-prog. We actually had someone working on a scheme for how to express this for programs some months ago, but unfortunately that stalled out (Jesper already knows this, but FYI to the rest of you). In any case, I view this as a "next step". Just exposing the feature bits to userspace will help users today, and as a side effect, this also makes drivers declare what they support, which we can then incorporate into the core code to, e.g., reject attachment of programs that won't work anyway. But let's do this in increments and not make the perfect the enemy of the good here. > BPF now have function calls and function replace right(?) How does > this affect this detection of possible return codes? It does have the same issue as tail calls, in that the return code of the function being replaced can obviously change. However, the verifier knows the target of a replace, so it can propagate any constraints put upon the caller if we implement it that way. -Toke
next prev parent reply other threads:[~2020-12-08 12:00 UTC|newest] Thread overview: 120+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-12-04 10:28 [PATCH v2 bpf 0/5] New netdev feature flags for XDP alardam 2020-12-04 10:28 ` [Intel-wired-lan] " alardam 2020-12-04 10:28 ` [PATCH v2 bpf 1/5] net: ethtool: add xdp properties flag set alardam 2020-12-04 10:28 ` [Intel-wired-lan] " alardam 2020-12-04 12:18 ` Toke Høiland-Jørgensen 2020-12-04 12:18 ` [Intel-wired-lan] " Toke =?unknown-8bit?q?H=C3=B8iland-J=C3=B8rgensen?= 2020-12-04 12:46 ` Maciej Fijalkowski 2020-12-04 12:46 ` [Intel-wired-lan] " Maciej Fijalkowski 2020-12-04 15:21 ` Daniel Borkmann 2020-12-04 15:21 ` [Intel-wired-lan] " Daniel Borkmann 2020-12-04 17:20 ` Toke Høiland-Jørgensen 2020-12-04 17:20 ` [Intel-wired-lan] " Toke =?unknown-8bit?q?H=C3=B8iland-J=C3=B8rgensen?= 2020-12-04 22:19 ` Daniel Borkmann 2020-12-04 22:19 ` [Intel-wired-lan] " Daniel Borkmann 2020-12-07 11:54 ` Jesper Dangaard Brouer 2020-12-07 11:54 ` [Intel-wired-lan] " Jesper Dangaard Brouer 2020-12-07 12:08 ` Toke Høiland-Jørgensen 2020-12-07 12:08 ` [Intel-wired-lan] " Toke =?unknown-8bit?q?H=C3=B8iland-J=C3=B8rgensen?= 2020-12-07 12:03 ` Toke Høiland-Jørgensen 2020-12-07 12:03 ` [Intel-wired-lan] " Toke =?unknown-8bit?q?H=C3=B8iland-J=C3=B8rgensen?= 2020-12-07 12:54 ` Jesper Dangaard Brouer 2020-12-07 12:54 ` [Intel-wired-lan] " Jesper Dangaard Brouer 2020-12-07 20:52 ` John Fastabend 2020-12-07 20:52 ` [Intel-wired-lan] " John Fastabend 2020-12-07 22:38 ` Saeed Mahameed 2020-12-07 22:38 ` [Intel-wired-lan] " Saeed Mahameed 2020-12-07 23:07 ` Maciej Fijalkowski 2020-12-07 23:07 ` [Intel-wired-lan] " Maciej Fijalkowski 2020-12-09 6:03 ` John Fastabend 2020-12-09 6:03 ` [Intel-wired-lan] " John Fastabend 2020-12-09 9:54 ` Maciej Fijalkowski 2020-12-09 9:54 ` [Intel-wired-lan] " Maciej Fijalkowski 2020-12-09 11:52 ` Jesper Dangaard Brouer 2020-12-09 11:52 ` [Intel-wired-lan] " Jesper Dangaard Brouer 2020-12-09 15:41 ` David Ahern 2020-12-09 15:41 ` [Intel-wired-lan] " David Ahern 2020-12-09 17:15 ` Saeed Mahameed 2020-12-09 17:15 ` [Intel-wired-lan] " Saeed Mahameed 2020-12-10 3:34 ` David Ahern 2020-12-10 3:34 ` [Intel-wired-lan] " David Ahern 2020-12-10 6:48 ` Saeed Mahameed 2020-12-10 6:48 ` [Intel-wired-lan] " Saeed Mahameed 2020-12-10 15:30 ` David Ahern 2020-12-10 15:30 ` [Intel-wired-lan] " David Ahern 2020-12-10 18:58 ` Saeed Mahameed 2020-12-10 18:58 ` [Intel-wired-lan] " Saeed Mahameed 2021-01-05 11:56 ` Marek Majtyka 2021-01-05 11:56 ` [Intel-wired-lan] " Marek Majtyka 2021-02-01 16:16 ` Toke Høiland-Jørgensen 2021-02-01 16:16 ` [Intel-wired-lan] " Toke =?unknown-8bit?q?H=C3=B8iland-J=C3=B8rgensen?= 2021-02-02 11:26 ` Marek Majtyka 2021-02-02 11:26 ` [Intel-wired-lan] " Marek Majtyka 2021-02-02 12:05 ` Toke Høiland-Jørgensen 2021-02-02 12:05 ` [Intel-wired-lan] " Toke =?unknown-8bit?q?H=C3=B8iland-J=C3=B8rgensen?= 2021-02-02 19:34 ` Jakub Kicinski 2021-02-02 19:34 ` [Intel-wired-lan] " Jakub Kicinski 2021-02-03 12:50 ` Marek Majtyka 2021-02-03 12:50 ` [Intel-wired-lan] " Marek Majtyka 2021-02-03 17:02 ` Jakub Kicinski 2021-02-03 17:02 ` [Intel-wired-lan] " Jakub Kicinski 2021-02-10 10:53 ` Toke Høiland-Jørgensen 2021-02-10 10:53 ` [Intel-wired-lan] " Toke =?unknown-8bit?q?H=C3=B8iland-J=C3=B8rgensen?= 2021-02-10 18:31 ` Jakub Kicinski 2021-02-10 18:31 ` [Intel-wired-lan] " Jakub Kicinski 2021-02-10 22:52 ` Toke Høiland-Jørgensen 2021-02-10 22:52 ` [Intel-wired-lan] " Toke =?unknown-8bit?q?H=C3=B8iland-J=C3=B8rgensen?= 2021-02-12 1:26 ` Jakub Kicinski 2021-02-12 1:26 ` [Intel-wired-lan] " Jakub Kicinski 2021-02-12 2:05 ` Alexei Starovoitov 2021-02-12 2:05 ` [Intel-wired-lan] " Alexei Starovoitov 2021-02-12 7:02 ` Marek Majtyka 2021-02-12 7:02 ` [Intel-wired-lan] " Marek Majtyka 2021-02-16 14:30 ` Toke Høiland-Jørgensen 2021-02-16 14:30 ` [Intel-wired-lan] " Toke =?unknown-8bit?q?H=C3=B8iland-J=C3=B8rgensen?= 2020-12-09 15:44 ` David Ahern 2020-12-09 15:44 ` [Intel-wired-lan] " David Ahern 2020-12-10 13:32 ` Explaining XDP redirect bulk size design (Was: [PATCH v2 bpf 1/5] net: ethtool: add xdp properties flag set) Jesper Dangaard Brouer 2020-12-10 13:32 ` [Intel-wired-lan] " Jesper Dangaard Brouer 2020-12-10 14:14 ` Magnus Karlsson 2020-12-10 14:14 ` Magnus Karlsson 2020-12-10 17:30 ` Jesper Dangaard Brouer 2020-12-10 17:30 ` Jesper Dangaard Brouer 2020-12-10 19:20 ` Saeed Mahameed 2020-12-10 19:20 ` [Intel-wired-lan] " Saeed Mahameed 2020-12-08 1:01 ` [PATCH v2 bpf 1/5] net: ethtool: add xdp properties flag set David Ahern 2020-12-08 1:01 ` [Intel-wired-lan] " David Ahern 2020-12-08 8:28 ` Jesper Dangaard Brouer 2020-12-08 8:28 ` [Intel-wired-lan] " Jesper Dangaard Brouer 2020-12-08 11:58 ` Toke Høiland-Jørgensen [this message] 2020-12-08 11:58 ` Toke =?unknown-8bit?q?H=C3=B8iland-J=C3=B8rgensen?= 2020-12-09 5:50 ` John Fastabend 2020-12-09 5:50 ` [Intel-wired-lan] " John Fastabend 2020-12-09 10:26 ` Toke Høiland-Jørgensen 2020-12-09 10:26 ` [Intel-wired-lan] " Toke =?unknown-8bit?q?H=C3=B8iland-J=C3=B8rgensen?= 2020-12-08 9:00 ` Jesper Dangaard Brouer 2020-12-08 9:00 ` [Intel-wired-lan] " Jesper Dangaard Brouer 2020-12-08 9:42 ` Daniel Borkmann 2020-12-08 9:42 ` [Intel-wired-lan] " Daniel Borkmann 2020-12-04 12:57 ` Maciej Fijalkowski 2020-12-04 12:57 ` [Intel-wired-lan] " Maciej Fijalkowski 2020-12-04 10:28 ` [PATCH v2 bpf 2/5] drivers/net: turn XDP properties on alardam 2020-12-04 10:28 ` [Intel-wired-lan] " alardam 2020-12-04 12:19 ` Toke Høiland-Jørgensen 2020-12-04 12:19 ` [Intel-wired-lan] " Toke =?unknown-8bit?q?H=C3=B8iland-J=C3=B8rgensen?= 2020-12-09 19:05 ` kernel test robot 2020-12-09 19:05 ` kernel test robot 2020-12-04 10:28 ` [PATCH v2 bpf 3/5] xsk: add usage of xdp properties flags alardam 2020-12-04 10:28 ` [Intel-wired-lan] " alardam 2020-12-04 10:29 ` [PATCH v2 bpf 4/5] xsk: add check for full support of XDP in bind alardam 2020-12-04 10:29 ` [Intel-wired-lan] " alardam 2020-12-04 10:29 ` [PATCH v2 bpf 5/5] ethtool: provide xdp info with XDP_PROPERTIES_GET alardam 2020-12-04 10:29 ` [Intel-wired-lan] " alardam 2020-12-04 17:20 ` [PATCH v2 bpf 0/5] New netdev feature flags for XDP Jakub Kicinski 2020-12-04 17:20 ` [Intel-wired-lan] " Jakub Kicinski 2020-12-04 17:26 ` Toke Høiland-Jørgensen 2020-12-04 17:26 ` [Intel-wired-lan] " Toke =?unknown-8bit?q?H=C3=B8iland-J=C3=B8rgensen?= 2020-12-04 19:22 ` Jakub Kicinski 2020-12-04 19:22 ` [Intel-wired-lan] " Jakub Kicinski 2020-12-07 12:04 ` Toke Høiland-Jørgensen 2020-12-07 12:04 ` [Intel-wired-lan] " Toke =?unknown-8bit?q?H=C3=B8iland-J=C3=B8rgensen?=
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