On 2/21/23 4:35 AM, Alexander Lobakin wrote:
From: Alexander Lobakin <aleksander.lobakin@xxxxxxxxx> Date: Mon, 20 Feb 2023 16:46:27 +0100&xdp_buff and &xdp_frame are bound in a way that xdp_buff->data_hard_start == xdp_frame It's always the case and e.g. xdp_convert_buff_to_frame() relies on this. IOW, the following: for (u32 i = 0; i < 0xdead; i++) { xdpf = xdp_convert_buff_to_frame(&xdp); xdp_convert_frame_to_buff(xdpf, &xdp); } shouldn't ever modify @xdpf's contents or the pointer itself. However, "live packet" code wrongly treats &xdp_frame as part of its context placed *before* the data_hard_start. With such flow, data_hard_start is sizeof(*xdpf) off to the right and no longer points to the XDP frame. Instead of replacing `sizeof(ctx)` with `offsetof(ctx, xdpf)` in several places and praying that there are no more miscalcs left somewhere in the code, unionize ::frm with ::data in a flex array, so that both starts pointing to the actual data_hard_start and the XDP frame actually starts being a part of it, i.e. a part of the headroom, not the context. A nice side effect is that the maximum frame size for this mode gets increased by 40 bytes, as xdp_buff::frame_sz includes everything from data_hard_start (-> includes xdpf already) to the end of XDP/skb shared info. Also update %MAX_PKT_SIZE accordingly in the selftests code. Leave it hardcoded for 64 bit && 4k pages, it can be made more flexible later on. Minor: align `&head->data` with how `head->frm` is assigned for consistency. Minor #2: rename 'frm' to 'frame' in &xdp_page_head while at it for clarity. (was found while testing XDP traffic generator on ice, which calls xdp_convert_frame_to_buff() for each XDP frame)Sorry, maybe this could be taken directly to net-next while it's still open? It was tested and then reverted from bpf-next only due to not 100% compile-time assertion, which I removed in this version. No more changes. I doubt there'll be a second PR from bpf and would like this to hit mainline before RC1 :s
I think this could go to bpf soon instead of bpf-next. The change is specific to the bpf selftest. It is better to go through bpf to get bpf CI coverage.
Fixes: b530e9e1063e ("bpf: Add "live packet" mode for XDP in BPF_PROG_RUN") Acked-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx> Signed-off-by: Alexander Lobakin <aleksander.lobakin@xxxxxxxxx> Link: https://lore.kernel.org/r/20230215185440.4126672-1-aleksander.lobakin@xxxxxxxxx Signed-off-by: Martin KaFai Lau <martin.lau@xxxxxxxxxx>(>_< those two last tags are incorrect, lemme know if I should resubmit it without them or you could do it if ok with taking it now)
Please respin when it can be landed to the bpf tree on top of the s390 changes.
