Jesper Dangaard Brouer <brouer@xxxxxxxxxx> writes: > The AF_XDP userspace part of xdp_hw_metadata see non-zero as a signal of > the availability of rx_timestamp and rx_hash in data_meta area. The > kernel-side BPF-prog code doesn't initialize these members when kernel > returns an error e.g. -EOPNOTSUPP. This memory area is not guaranteed to > be zeroed, and can contain garbage/previous values, which will be read > and interpreted by AF_XDP userspace side. > > Tested this on different drivers. The experiences are that for most > packets they will have zeroed this data_meta area, but occasionally it > will contain garbage data. > > Example of failure tested on ixgbe: > poll: 1 (0) > xsk_ring_cons__peek: 1 > 0x18ec788: rx_desc[0]->addr=100000000008000 addr=8100 comp_addr=8000 > rx_hash: 3697961069 > rx_timestamp: 9024981991734834796 (sec:9024981991.7348) > 0x18ec788: complete idx=8 addr=8000 > > Converting to date: > date -d @9024981991 > 2255-12-28T20:26:31 CET > > I choose a simple fix in this patch. When kfunc fails or isn't supported > assign zero to the corresponding struct meta value. > > It's up to the individual BPF-programmer to do something smarter e.g. > that fits their use-case, like getting a software timestamp and marking > a flag that gives the type of timestamp. > > Another possibility is for the behavior of kfunc's > bpf_xdp_metadata_rx_timestamp and bpf_xdp_metadata_rx_hash to require > clearing return value pointer. I definitely think we should leave it up to the BPF programmer to react to failures; that's what the return code is there for, after all :) -Toke
