netdev - Re: [RFC net-next 6/8] nfp: bpf: add support for XDP_FLAGS_HW

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Date:   Mon, 19 Jun 2017 17:01:23 -0700
From:   Jakub Kicinski <kubakici@...pl>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, kafai@...com,
        brouer@...hat.com, oss-drivers@...ronome.com
Subject: Re: [RFC net-next 6/8] nfp: bpf: add support for XDP_FLAGS_HW_MODE

On Tue, 20 Jun 2017 01:50:17 +0200, Daniel Borkmann wrote:
> On 06/17/2017 01:57 AM, Jakub Kicinski wrote:
> > Respect the XDP_FLAGS_HW_MODE.  When it's set install the program
> > on the NIC and skip enabling XDP in the driver.
> >
> > Signed-off-by: Jakub Kicinski <jakub.kicinski@...ronome.com>
> > ---
> >   drivers/net/ethernet/netronome/nfp/nfp_net_common.c | 10 +++++++---
> >   1 file changed, 7 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/netronome/nfp/nfp_net_common.c b/drivers/net/ethernet/netronome/nfp/nfp_net_common.c
> > index 68648e312129..c5903b6e58c5 100644
> > --- a/drivers/net/ethernet/netronome/nfp/nfp_net_common.c
> > +++ b/drivers/net/ethernet/netronome/nfp/nfp_net_common.c
> > @@ -3310,19 +3310,22 @@ static int
> >   nfp_net_xdp_setup(struct nfp_net *nn, struct bpf_prog *prog, u32 flags,
> >   		  struct netlink_ext_ack *extack)
> >   {
> > -	struct bpf_prog *offload_prog;
> > +	struct bpf_prog *drv_prog, *offload_prog;
> >   	int err;
> >
> >   	if (nn->xdp_prog && (flags ^ nn->xdp_flags) & XDP_FLAGS_MODES)
> >   		return -EBUSY;
> >
> > +	drv_prog     = flags & XDP_FLAGS_HW_MODE  ? NULL : prog;
> >   	offload_prog = flags & XDP_FLAGS_DRV_MODE ? NULL : prog;  
> 
> Can you make this assumption here? If dev_change_xdp_fd() is called
> without XDP_FLAGS_HW_MODE or XDP_FLAGS_DRV_MODE flags, then we set prog
> to both, drv_prog and offload_prog. Is this expected?
> 
> Maybe in nfp_net_xdp_setup() check for !hweight32(xdp_flags & XDP_FLAGS_MODES)
> and then set flags |= XDP_FLAGS_DRV_MODE before both assignments?

I thought we did want both.  In case the program is loaded to both the
HW/FW will mark the packets with BPF bit in the descriptor so that they
are not processed twice.  But the driver path will be configured for
running bpf and when user replaces the program with one which cannot be
offloaded the driver will not have to reconfigure itself.