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Message-ID: <CAJ+HfNg947QSVoQ_jV27PAC5EErK5kVdrA3=6WEY=fxdve-QRw@mail.gmail.com>
Date: Thu, 23 May 2019 08:35:13 +0200
From: Björn Töpel <bjorn.topel@...il.com>
To: Saeed Mahameed <saeedm@...lanox.com>
Cc: "toke@...hat.com" <toke@...hat.com>,
"daniel@...earbox.net" <daniel@...earbox.net>,
"ast@...nel.org" <ast@...nel.org>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
"magnus.karlsson@...el.com" <magnus.karlsson@...el.com>,
"bjorn.topel@...el.com" <bjorn.topel@...el.com>,
"jakub.kicinski@...ronome.com" <jakub.kicinski@...ronome.com>,
"brouer@...hat.com" <brouer@...hat.com>,
"bpf@...r.kernel.org" <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf-next 1/2] net: xdp: refactor XDP_QUERY_PROG{,_HW} to netdev
On Thu, 23 May 2019 at 07:47, Saeed Mahameed <saeedm@...lanox.com> wrote:
>
> On Wed, 2019-05-22 at 14:53 +0200, Björn Töpel wrote:
> > From: Björn Töpel <bjorn.topel@...el.com>
> >
> > All XDP capable drivers need to implement the XDP_QUERY_PROG{,_HW}
> > command of ndo_bpf. The query code is fairly generic. This commit
> > refactors the query code up from the drivers to the netdev level.
> >
> > The struct net_device has gained four new members tracking the XDP
> > program, the corresponding program flags, and which programs
> > (SKB_MODE, DRV_MODE or HW_MODE) that are activated.
> >
> > The xdp_prog member, previously only used for SKB_MODE, is shared
> > with
> > DRV_MODE, since they are mutually exclusive.
> >
> > The program query operations is all done under the rtnl lock.
> > However,
> > the xdp_prog member is __rcu annotated, and used in a lock-less
> > manner
> > for the SKB_MODE. This is because the xdp_prog member is shared from
> > a
> > query program perspective (again, SKB and DRV are mutual exclusive),
> > RCU read and assignments functions are still used when altering
> > xdp_prog, even when only for queries in DRV_MODE. This is for
> > sparse/lockdep correctness.
> >
> > A minor behavioral change was done during this refactorization; When
> > passing a negative file descriptor to a netdev to disable XDP, the
> > same program flag as the running program is required. An example.
> >
> > The eth0 is DRV_DRV capable. Previously, this was OK, but confusing:
> >
> > # ip link set dev eth0 xdp obj foo.o sec main
> > # ip link set dev eth0 xdpgeneric off
> >
> > Now, the same commands give:
> >
> > # ip link set dev eth0 xdp obj foo.o sec main
> > # ip link set dev eth0 xdpgeneric off
> > Error: native and generic XDP can't be active at the same time.
> >
> > Signed-off-by: Björn Töpel <bjorn.topel@...el.com>
> > ---
> > include/linux/netdevice.h | 13 +++--
> > net/core/dev.c | 120 ++++++++++++++++++++--------------
> > ----
> > net/core/rtnetlink.c | 33 ++---------
> > 3 files changed, 76 insertions(+), 90 deletions(-)
> >
> > diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> > index 44b47e9df94a..bdcb20a3946c 100644
> > --- a/include/linux/netdevice.h
> > +++ b/include/linux/netdevice.h
> > @@ -1940,6 +1940,11 @@ struct net_device {
> > #endif
> > struct hlist_node index_hlist;
> >
> > + struct bpf_prog *xdp_prog_hw;
> > + unsigned int xdp_flags;
> > + u32 xdp_prog_flags;
> > + u32 xdp_prog_hw_flags;
> > +
>
>
> Maybe it will be nicer if you wrap all xdp related data in one struct,
> This is good as a weak enforcement so future xdp extensions will go to
> the same place and not spread all across the net_device struct.
>
> this is going to be handy when we start introducing XDP offloads.
>
> > /*
> > * Cache lines mostly used on transmit path
> > */
> > @@ -2045,9 +2050,8 @@ struct net_device {
> >
> > static inline bool netif_elide_gro(const struct net_device *dev)
> > {
> > - if (!(dev->features & NETIF_F_GRO) || dev->xdp_prog)
> > - return true;
> > - return false;
> > + return !(dev->features & NETIF_F_GRO) ||
> > + dev->xdp_flags & XDP_FLAGS_SKB_MODE;
> > }
> >
> > #define NETDEV_ALIGN 32
> > @@ -3684,8 +3688,7 @@ struct sk_buff *dev_hard_start_xmit(struct
> > sk_buff *skb, struct net_device *dev,
> > typedef int (*bpf_op_t)(struct net_device *dev, struct netdev_bpf
> > *bpf);
> > int dev_change_xdp_fd(struct net_device *dev, struct netlink_ext_ack
> > *extack,
> > int fd, u32 flags);
> > -u32 __dev_xdp_query(struct net_device *dev, bpf_op_t xdp_op,
> > - enum bpf_netdev_command cmd);
> > +u32 dev_xdp_query(struct net_device *dev, unsigned int flags);
> > int xdp_umem_query(struct net_device *dev, u16 queue_id);
> >
> > int __dev_forward_skb(struct net_device *dev, struct sk_buff *skb);
> > diff --git a/net/core/dev.c b/net/core/dev.c
> > index b6b8505cfb3e..ead16c3f955c 100644
> > --- a/net/core/dev.c
> > +++ b/net/core/dev.c
> > @@ -8005,31 +8005,31 @@ int dev_change_proto_down_generic(struct
> > net_device *dev, bool proto_down)
> > }
> > EXPORT_SYMBOL(dev_change_proto_down_generic);
> >
> > -u32 __dev_xdp_query(struct net_device *dev, bpf_op_t bpf_op,
> > - enum bpf_netdev_command cmd)
> > +u32 dev_xdp_query(struct net_device *dev, unsigned int flags)
> > {
> > - struct netdev_bpf xdp;
> > + struct bpf_prog *prog = NULL;
> >
> > - if (!bpf_op)
> > + if (hweight32(flags) != 1)
> > return 0;
> >
> > - memset(&xdp, 0, sizeof(xdp));
> > - xdp.command = cmd;
> > -
> > - /* Query must always succeed. */
> > - WARN_ON(bpf_op(dev, &xdp) < 0 && cmd == XDP_QUERY_PROG);
>
> since now this function can only query PROG or PROG_HW it is a good
> time to reflect that in the function name, maybe dev_xdp_query_prog is
> a better name ?
>
> > + if (flags & (XDP_FLAGS_SKB_MODE | XDP_FLAGS_DRV_MODE))
> > + prog = rtnl_dereference(dev->xdp_prog);
> > + else if (flags & XDP_FLAGS_HW_MODE)
> > + prog = dev->xdp_prog_hw;
> >
> > - return xdp.prog_id;
> > + return prog ? prog->aux->id : 0;
> > }
> >
> > -static int dev_xdp_install(struct net_device *dev, bpf_op_t bpf_op,
> > +static int dev_xdp_install(struct net_device *dev, unsigned int
> > target,
> > struct netlink_ext_ack *extack, u32 flags,
> > struct bpf_prog *prog)
> > {
> > + bpf_op_t bpf_op = dev->netdev_ops->ndo_bpf;
>
> I would assing bpf_op below :
> bpf_op = (target == XDP_FLAGS_SKB_MODE) ?
> generic_xdp_install :
> dev->netdev_ops->ndo_bpf;
>
> or just drop bpf_op and call dev->netdev_ops->ndo_bpf in the one place
> it bpf_op is being called.
>
> > struct netdev_bpf xdp;
> > + int err;
> >
> > memset(&xdp, 0, sizeof(xdp));
> > - if (flags & XDP_FLAGS_HW_MODE)
> > + if (target == XDP_FLAGS_HW_MODE)
> > xdp.command = XDP_SETUP_PROG_HW;
> > else
> > xdp.command = XDP_SETUP_PROG;
> > @@ -8037,35 +8037,41 @@ static int dev_xdp_install(struct net_device
> > *dev, bpf_op_t bpf_op,
> > xdp.flags = flags;
> > xdp.prog = prog;
>
> Are you sure no one is using flags
> >
> > - return bpf_op(dev, &xdp);
> > + err = (target == XDP_FLAGS_SKB_MODE) ?
> > + generic_xdp_install(dev, &xdp) :
> > + bpf_op(dev, &xdp);
> > + if (!err) {
> > + if (prog)
> > + dev->xdp_flags |= target;
> > + else
> > + dev->xdp_flags &= ~target;
> > +
> > + if (target == XDP_FLAGS_HW_MODE) {
> > + dev->xdp_prog_hw = prog;
> > + dev->xdp_prog_hw_flags = flags;
> > + } else if (target == XDP_FLAGS_DRV_MODE) {
> > + rcu_assign_pointer(dev->xdp_prog, prog);
> > + dev->xdp_prog_flags = flags;
> > + }
> > + }
> > +
> > + return err;
> > }
> >
> > static void dev_xdp_uninstall(struct net_device *dev)
> > {
> > - struct netdev_bpf xdp;
> > - bpf_op_t ndo_bpf;
> > -
> > - /* Remove generic XDP */
> > - WARN_ON(dev_xdp_install(dev, generic_xdp_install, NULL, 0,
> > NULL));
> > -
> > - /* Remove from the driver */
> > - ndo_bpf = dev->netdev_ops->ndo_bpf;
> > - if (!ndo_bpf)
> > - return;
> > -
> > - memset(&xdp, 0, sizeof(xdp));
> > - xdp.command = XDP_QUERY_PROG;
> > - WARN_ON(ndo_bpf(dev, &xdp));
> > - if (xdp.prog_id)
> > - WARN_ON(dev_xdp_install(dev, ndo_bpf, NULL,
> > xdp.prog_flags,
> > - NULL));
> > -
> > - /* Remove HW offload */
> > - memset(&xdp, 0, sizeof(xdp));
> > - xdp.command = XDP_QUERY_PROG_HW;
> > - if (!ndo_bpf(dev, &xdp) && xdp.prog_id)
> > - WARN_ON(dev_xdp_install(dev, ndo_bpf, NULL,
> > xdp.prog_flags,
> > - NULL));
> > + if (dev->xdp_flags & XDP_FLAGS_SKB_MODE) {
> > + WARN_ON(dev_xdp_install(dev, XDP_FLAGS_SKB_MODE,
> > + NULL, 0, NULL));
> > + }
> > + if (dev->xdp_flags & XDP_FLAGS_DRV_MODE) {
> > + WARN_ON(dev_xdp_install(dev, XDP_FLAGS_DRV_MODE,
> > + NULL, dev->xdp_prog_flags,
> > NULL));
> > + }
> > + if (dev->xdp_flags & XDP_FLAGS_HW_MODE) {
> > + WARN_ON(dev_xdp_install(dev, XDP_FLAGS_HW_MODE,
> > + NULL, dev->xdp_prog_hw_flags,
> > NULL));
> > + }
>
> instead this long "if" dance, why don't you just use xdp->flags inside
> dev_xdp_install when prog is NULL ?
> I would even consider introducing an uninstall function, which doesn't
> receive flags, and will use xdp->flags directly..
>
> uninstall can be just a two liner function
>
> dev_xdp_uninstall() {
> xdp.prog = NULL;
> (dev->xdp_flags == XDP_FLAGS_SKB_MODE) ?
> generic_xdp_install(dev, &xdp) :
> dev->netdev_ops->ndo_bpf(dev, &xdp);
> dev->xdp_flags &= ~(XDP_FLAGS_SKB_MODE | XDP_FLAGS_HW_MODE |
> XDP_FLAGS_DRV_MODE);
> }
>
> > }
> >
> > /**
> > @@ -8080,41 +8086,41 @@ static void dev_xdp_uninstall(struct
> > net_device *dev)
> > int dev_change_xdp_fd(struct net_device *dev, struct netlink_ext_ack
> > *extack,
> > int fd, u32 flags)
> > {
> > - const struct net_device_ops *ops = dev->netdev_ops;
> > - enum bpf_netdev_command query;
> > + bool offload, drv_supp = !!dev->netdev_ops->ndo_bpf;
> > struct bpf_prog *prog = NULL;
> > - bpf_op_t bpf_op, bpf_chk;
> > - bool offload;
> > + unsigned int target;
> > int err;
> >
> > ASSERT_RTNL();
> >
> > offload = flags & XDP_FLAGS_HW_MODE;
> > - query = offload ? XDP_QUERY_PROG_HW : XDP_QUERY_PROG;
> > + target = offload ? XDP_FLAGS_HW_MODE : XDP_FLAGS_DRV_MODE;
>
> I don't think you really need this target parameter it only complicates
> things for no reason, all information you need are already in flags and
> dev->xdp_flags.
>
> >
> > - bpf_op = bpf_chk = ops->ndo_bpf;
> > - if (!bpf_op && (flags & (XDP_FLAGS_DRV_MODE |
> > XDP_FLAGS_HW_MODE))) {
> > + if (!drv_supp && (flags & (XDP_FLAGS_DRV_MODE |
> > XDP_FLAGS_HW_MODE))) {
> > NL_SET_ERR_MSG(extack, "underlying driver does not
> > support XDP in native mode");
> > return -EOPNOTSUPP;
> > }
> > - if (!bpf_op || (flags & XDP_FLAGS_SKB_MODE))
> > - bpf_op = generic_xdp_install;
> > - if (bpf_op == bpf_chk)
> > - bpf_chk = generic_xdp_install;
> > +
> > + if (!drv_supp || (flags & XDP_FLAGS_SKB_MODE))
> > + target = XDP_FLAGS_SKB_MODE;
> > +
>
> since dev_xdp_install handles all cases now, you don't need this logic
> here, I would move this into dev_xdp_install, maybe introduce a helper
> dedicated function to choose the mode to be used.
>
> > + if ((target == XDP_FLAGS_SKB_MODE &&
> > + dev->xdp_flags & XDP_FLAGS_DRV_MODE) ||
> > + (target == XDP_FLAGS_DRV_MODE &&
> > + dev->xdp_flags & XDP_FLAGS_SKB_MODE)) {
> > + NL_SET_ERR_MSG(extack, "native and generic XDP can't be
> > active at the same time");
> > + return -EEXIST;
> > + }
> >
> > if (fd >= 0) {
> > - if (!offload && __dev_xdp_query(dev, bpf_chk,
> > XDP_QUERY_PROG)) {
> > - NL_SET_ERR_MSG(extack, "native and generic XDP
> > can't be active at the same time");
> > - return -EEXIST;
> > - }
> > - if ((flags & XDP_FLAGS_UPDATE_IF_NOEXIST) &&
> > - __dev_xdp_query(dev, bpf_op, query)) {
> > + if (flags & XDP_FLAGS_UPDATE_IF_NOEXIST &&
> > + dev_xdp_query(dev, target)) {
> > NL_SET_ERR_MSG(extack, "XDP program already
> > attached");
> > return -EBUSY;
> > }
> >
> > - prog = bpf_prog_get_type_dev(fd, BPF_PROG_TYPE_XDP,
> > - bpf_op == ops->ndo_bpf);
> > + prog = bpf_prog_get_type_dev(fd, BPF_PROG_TYPE_XDP,
> > drv_supp);
> > +
> > if (IS_ERR(prog))
> > return PTR_ERR(prog);
> >
> > @@ -8125,7 +8131,7 @@ int dev_change_xdp_fd(struct net_device *dev,
> > struct netlink_ext_ack *extack,
> > }
> > }
> >
> > - err = dev_xdp_install(dev, bpf_op, extack, flags, prog);
> > + err = dev_xdp_install(dev, target, extack, flags, prog);
> > if (err < 0 && prog)
> > bpf_prog_put(prog);
> >
> > diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
> > index adcc045952c2..99ca58db297f 100644
> > --- a/net/core/rtnetlink.c
> > +++ b/net/core/rtnetlink.c
> > @@ -1360,37 +1360,14 @@ static int rtnl_fill_link_ifmap(struct
> > sk_buff *skb, struct net_device *dev)
> > return 0;
> > }
> >
> > -static u32 rtnl_xdp_prog_skb(struct net_device *dev)
> > -{
> > - const struct bpf_prog *generic_xdp_prog;
> > -
> > - ASSERT_RTNL();
> > -
> > - generic_xdp_prog = rtnl_dereference(dev->xdp_prog);
> > - if (!generic_xdp_prog)
> > - return 0;
> > - return generic_xdp_prog->aux->id;
> > -}
> > -
> > -static u32 rtnl_xdp_prog_drv(struct net_device *dev)
> > -{
> > - return __dev_xdp_query(dev, dev->netdev_ops->ndo_bpf,
> > XDP_QUERY_PROG);
> > -}
> > -
> > -static u32 rtnl_xdp_prog_hw(struct net_device *dev)
> > -{
> > - return __dev_xdp_query(dev, dev->netdev_ops->ndo_bpf,
> > - XDP_QUERY_PROG_HW);
> > -}
> > -
> > static int rtnl_xdp_report_one(struct sk_buff *skb, struct
> > net_device *dev,
> > u32 *prog_id, u8 *mode, u8 tgt_mode, u32
> > attr,
> > - u32 (*get_prog_id)(struct net_device
> > *dev))
> > + unsigned int tgt_flags)
> > {
> > u32 curr_id;
> > int err;
> >
> > - curr_id = get_prog_id(dev);
> > + curr_id = dev_xdp_query(dev, tgt_flags);
> > if (!curr_id)
> > return 0;
> >
> > @@ -1421,15 +1398,15 @@ static int rtnl_xdp_fill(struct sk_buff *skb,
> > struct net_device *dev)
> > prog_id = 0;
> > mode = XDP_ATTACHED_NONE;
> > err = rtnl_xdp_report_one(skb, dev, &prog_id, &mode,
> > XDP_ATTACHED_SKB,
> > - IFLA_XDP_SKB_PROG_ID,
> > rtnl_xdp_prog_skb);
> > + IFLA_XDP_SKB_PROG_ID,
> > XDP_FLAGS_SKB_MODE);
> > if (err)
> > goto err_cancel;
> > err = rtnl_xdp_report_one(skb, dev, &prog_id, &mode,
> > XDP_ATTACHED_DRV,
> > - IFLA_XDP_DRV_PROG_ID,
> > rtnl_xdp_prog_drv);
> > + IFLA_XDP_DRV_PROG_ID,
> > XDP_FLAGS_DRV_MODE);
> > if (err)
> > goto err_cancel;
> > err = rtnl_xdp_report_one(skb, dev, &prog_id, &mode,
> > XDP_ATTACHED_HW,
> > - IFLA_XDP_HW_PROG_ID,
> > rtnl_xdp_prog_hw);
> > + IFLA_XDP_HW_PROG_ID,
> > XDP_FLAGS_HW_MODE);
> > if (err)
> > goto err_cancel;
> >
Saeed, thanks a lot for your comments! All good stuff. I'll address
them in the next version!
Thanks,
Björn
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