Lorenzo Bianconi <lorenzo.bianconi@xxxxxxxxxx> writes: >> On Wed, 28 Nov 2018 13:36:26 +0100 >> Toke Høiland-Jørgensen <toke@xxxxxxx> wrote: >> >> > Lorenzo Bianconi <lorenzo.bianconi@xxxxxxxxxx> writes: >> > >> > >> Lorenzo Bianconi <lorenzo.bianconi@xxxxxxxxxx> writes: >> > >> >> > >> > This series is intended as a playground to start experimenting/developing >> > >> > with XDP/eBPF over WiFi and collect ideas/concerns about it. >> > >> > Introduce XDP support to mt76x2e/mt76x0e drivers. Currently supported >> > >> > actions are: >> > >> > - XDP_PASS >> > >> > - XDP_ABORTED >> > >> > - XDP_DROP >> > >> > Introduce ndo_bpf mac80211 callback in order to to load a bpf >> > >> > program into low level driver XDP rx hook. >> > >> > This series has been tested through a simple bpf program (available here: >> > >> > https://github.com/LorenzoBianconi/bpf-workspace/tree/master/mt76_xdp_stats) >> > >> > used to count frame types received by the device. >> > >> > Possible eBPF use cases could be: >> > >> > - implement new statistics through bpf maps >> > >> > - implement fast packet filtering (e.g in monitor mode) >> > >> > - ... >> > > >> > > Hi Kalle, >> > > >> > >> >> > >> This is most likely a stupid question, but why do this in the driver and >> > >> not in mac80211 so that all drivers could benefit from it? I guess there >> > >> are reasons for that, I just can't figure that out. >> > >> > XDP achieves its speedup by running the eBPF program inside the driver >> > NAPI loop, before the kernel even touches the data in any other capacity >> > (and in particular, before it allocates an SKB). Which kinda means the >> > hook needs to be in the driver... Could be a fallback in mac80211, >> > though; although we'd have to figure out how that interacts with Generic >> > XDP. >> > >> > > This is an early stage implementation, at this point I would collect >> > > other people opinions/concerns about using bpf/xdp directly on 802.11 >> > > frames. >> > >> > Thanks for looking into this! >> > >> > I have two concerns with running XDP on 802.11 frames: >> > >> > 1. It makes it more difficult to add other XDP actions (such as >> > REDIRECT), as the XDP program would then have to make sure that the >> > outer packet headers are removed before, say, redirecting the packet >> > out of an ethernet interface. Also, if we do add redirect, we would >> > be bypassing mac80211 entirely; to what extent would that mess up >> > internal state? >> > >> > 2. UI consistency; suddenly, the user needs to know which kind of >> > frames to expect, and XDP program reuse becomes more difficult. This >> > may be unavoidable given the nature of XDP, but some thought needs to >> > go into this. Especially since we wouldn't necessarily be consistent >> > between WiFi drivers (there are fullmac devices that remove 802.11 >> > headers before sending up the frame, right?). >> > >> > >> > Adding in Jesper; maybe he has some thoughts on this? > > Hi Jesper, > >> >> Today XDP assumes the frame is an Ethernet frame. With WiFi I guess >> this assumption change, right? > > yes correct, SoftMAC devices report 802.11 frames to the stack > >> I worry a bit about this, as XDP is all about performance, and I don't >> want to add performance regressions, by requiring all XDP programs or >> core-code to having to check-frame-type before proceeding. That said, I >> do think it is doable, without adding performance regressions. >> >> Option #1 is to move the check-frame-type to setup time. By either >> having frame-type be part of eBPF prog, or supply frame-type as option >> XDP attach call. And then reject attaching XDP prog to a device, where >> the expected frame-type does not match. >> > > I guess it will be enough to avoid loading a 'non-WiFi' bpf program on > a 802.11 netdevice (and vice versa). We could add a flag (or something > similar) in XDP_SETUP_PROG section of netdev_bpf data structure and > use ieee80211_ptr netdevice pointer in order to guarantee that the bpf > program will work on the expected 'frame-type' Yeah, a flag would be good; we've been discussing that for other XDP use cases; it's not a done deal yet, but I think it would be useful. > >> Option#2, leave it up to eBPF-programmer if they want to add runtime >> checks. By extending xdp_rxq_info with frame-type (default to >> Ethernet), which allow the eBPF-programmer choose to write a generic >> XDP program that both work on Ethernet and WiFi, or skip-check as they >> know this will e.g. only run on Wifi. (Note xdp_rxq_info is static >> read-only info per RX-queue, will all Wifi frames have same frame-type?. >> > > 802.11 standards define three frame subtype (data, management and control). > Subtypes could be detected parsing 802.11 header > >> >> Also consider what happens in case of XDP_REDIRECT, from a Wifi NIC to >> an Ethernet NIC. It would of-cause be cool to get this working cross, >> Wifi-Ethernet. >> > > Very cool :) On tx side the driver will accept standard ethernet frames in > ndo_xdp_xmit pointer How do you envision that will work with drivers that build software 802.11 frames? The TX hook would have to be in mac80211 somewhere, wouldn't it? >> Option#3 is to say, Wifi XDP is so different that we should create a >> new (enum) bpf_prog_type. And then still see if we can leverage some >> of the same core-code (as long as it doesn't slowdown performance). >> > > Do you think that Option#3 will be more 'future-proof' respect to > Option#1? My feeling is that WiFi devices are not sufficiently different to warrant a whole new program type. We risk combinatorial explosion for all the stuff that is the same, but now need to be tested for two (or N) types... -Toke
