On Thu, Jul 13, 2023 at 04:02:42PM -0700, Alexei Starovoitov wrote:
> On Thu, Jul 13, 2023 at 11:59 AM Maciej Fijalkowski
> <maciej.fijalkowski@xxxxxxxxx> wrote:
> >
> > On Mon, Jul 10, 2023 at 06:09:28PM -0700, Alexei Starovoitov wrote:
> > > On Thu, Jul 6, 2023 at 1:47 PM Maciej Fijalkowski
> > > <maciej.fijalkowski@xxxxxxxxx> wrote:
> > > >
> > > > Introduce new netlink attribute NETDEV_A_DEV_XDP_ZC_MAX_SEGS that will
> > > > carry maximum fragments that underlying ZC driver is able to handle on
> > > > TX side. It is going to be included in netlink response only when driver
> > > > supports ZC. Any value higher than 1 implies multi-buffer ZC support on
> > > > underlying device.
> > > >
> > > > Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@xxxxxxxxx>
> > >
> > > I suspect something in this patch makes XDP bonding test fail.
> > > See BPF CI.
> > >
> > > I can reproduce the failure locally as well.
> > > test_progs -t bond
> > > works without the series and fails with them.
> >
> > Hi Alexei,
> >
> > this fails on second bpf_xdp_query() call due to non-zero (?) contents at the
> > end of bpf_xdp_query_opts struct - currently it looks as following:
> >
> > $ pahole -C bpf_xdp_query_opts libbpf.so
> > struct bpf_xdp_query_opts {
> > size_t sz; /* 0 8 */
> > __u32 prog_id; /* 8 4 */
> > __u32 drv_prog_id; /* 12 4 */
> > __u32 hw_prog_id; /* 16 4 */
> > __u32 skb_prog_id; /* 20 4 */
> > __u8 attach_mode; /* 24 1 */
> >
> > /* XXX 7 bytes hole, try to pack */
> >
> > __u64 feature_flags; /* 32 8 */
> > __u32 xdp_zc_max_segs; /* 40 4 */
> >
> > /* size: 48, cachelines: 1, members: 8 */
> > /* sum members: 37, holes: 1, sum holes: 7 */
> > /* padding: 4 */
> > /* last cacheline: 48 bytes */
> > };
> >
> > Fix is either to move xdp_zc_max_segs up to existing hole or to zero out
> > struct before bpf_xdp_query() calls, like:
> >
> > memset(&query_opts, 0, sizeof(struct bpf_xdp_query_opts));
> > query_opts.sz = sizeof(struct bpf_xdp_query_opts);
>
> Right. That would be good to have to clear the hole,
> but probably unrelated.
>
> > I am kinda confused as this is happening due to two things. First off
> > bonding driver sets its xdp_features to NETDEV_XDP_ACT_MASK and in turn
> > this implies ZC feature enabled which makes xdp_zc_max_segs being included
> > in the response (it's value is 1 as it's the default).
> >
> > Then, offsetofend(struct type, type##__last_field) that is used as one of
> > libbpf_validate_opts() args gives me 40 but bpf_xdp_query_opts::sz has
> > stored 48, so in the end we go through the last 8 bytes in
> > libbpf_is_mem_zeroed() and we hit the '1' from xdp_zc_max_segs.
>
> Because this patch didn't update
> bpf_xdp_query_opts__last_field
Heh, bummer, this was right in front of me whole time. I think I need a
break:) but before that let me send v6. Thanks Alexei.
>
> It added a new field, but didn't update the macro.
>
> > So, (silly) questions:
> > - why bonding driver defaults to all features enabled?
>
> doesn't really matter in this context.
>
> > - why __last_field does not recognize xdp_zc_max_segs at the end?
>
> because the patch didn't update it :)
>
> > Besides, I think i'll move xdp_zc_max_segs above to the hole. This fixes
> > the bonding test for me.
>
> No. Keep it at the end.
