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Date: Fri, 19 Feb 2021 18:10:40 +0100
From: Toke Høiland-Jørgensen <toke@...hat.com>
To: Björn Töpel <bjorn.topel@...il.com>,
ast@...nel.org, daniel@...earbox.net, netdev@...r.kernel.org,
bpf@...r.kernel.org
Cc: Björn Töpel <bjorn.topel@...el.com>,
maciej.fijalkowski@...el.com, hawk@...nel.org,
magnus.karlsson@...el.com, john.fastabend@...il.com,
kuba@...nel.org, davem@...emloft.net
Subject: Re: [PATCH bpf-next 2/2] bpf, xdp: restructure redirect actions
Björn Töpel <bjorn.topel@...il.com> writes:
> From: Björn Töpel <bjorn.topel@...el.com>
>
> The XDP_REDIRECT implementations for maps and non-maps are fairly
> similar, but obviously need to take different code paths depending on
> if the target is using a map or not. Today, the redirect targets for
> XDP either uses a map, or is based on ifindex.
>
> Here, an explicit redirect type is added to bpf_redirect_info, instead
> of the actual map. Redirect type, map item/ifindex, and the map_id (if
> any) is passed to xdp_do_redirect().
>
> In addition to making the code easier to follow, using an explicit
> type in bpf_redirect_info has a slight positive performance impact by
> avoiding a pointer indirection for the map type lookup, and instead
> use the cacheline for bpf_redirect_info.
>
> Since the actual map is not passed via bpf_redirect_info anymore, the
> map lookup is only done in the BPF helper. This means that the
> bpf_clear_redirect_map() function can be removed. The actual map item
> is RCU protected.
>
> The bpf_redirect_info flags member is not used by XDP, and not
> read/written any more. The map member is only written to when
> required/used, and not unconditionally.
>
> rfc->v1: Use map_id, and remove bpf_clear_redirect_map(). (Toke)
>
> Reviewed-by: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
> Signed-off-by: Björn Töpel <bjorn.topel@...el.com>
Very cool! Also a small nit below, but otherwise:
Acked-by: Toke Høiland-Jørgensen <toke@...hat.com>
> ---
> include/linux/filter.h | 11 ++-
> include/trace/events/xdp.h | 66 +++++++++------
> kernel/bpf/cpumap.c | 1 -
> kernel/bpf/devmap.c | 1 -
> net/core/filter.c | 162 ++++++++++++++++---------------------
> net/xdp/xskmap.c | 1 -
> 6 files changed, 121 insertions(+), 121 deletions(-)
>
> diff --git a/include/linux/filter.h b/include/linux/filter.h
> index 1dedcf66b694..1f3cf2a1e116 100644
> --- a/include/linux/filter.h
> +++ b/include/linux/filter.h
> @@ -646,11 +646,20 @@ struct bpf_redirect_info {
> u32 flags;
> u32 tgt_index;
> void *tgt_value;
> - struct bpf_map *map;
> + u32 map_id;
> + u32 tgt_type;
> u32 kern_flags;
> struct bpf_nh_params nh;
> };
>
> +enum xdp_redirect_type {
> + XDP_REDIR_UNSET,
> + XDP_REDIR_DEV_IFINDEX,
> + XDP_REDIR_DEV_MAP,
> + XDP_REDIR_CPU_MAP,
> + XDP_REDIR_XSK_MAP,
> +};
> +
> DECLARE_PER_CPU(struct bpf_redirect_info, bpf_redirect_info);
>
> /* flags for bpf_redirect_info kern_flags */
> diff --git a/include/trace/events/xdp.h b/include/trace/events/xdp.h
> index 76a97176ab81..538321735447 100644
> --- a/include/trace/events/xdp.h
> +++ b/include/trace/events/xdp.h
> @@ -86,19 +86,15 @@ struct _bpf_dtab_netdev {
> };
> #endif /* __DEVMAP_OBJ_TYPE */
>
> -#define devmap_ifindex(tgt, map) \
> - (((map->map_type == BPF_MAP_TYPE_DEVMAP || \
> - map->map_type == BPF_MAP_TYPE_DEVMAP_HASH)) ? \
> - ((struct _bpf_dtab_netdev *)tgt)->dev->ifindex : 0)
> -
> DECLARE_EVENT_CLASS(xdp_redirect_template,
>
> TP_PROTO(const struct net_device *dev,
> const struct bpf_prog *xdp,
> const void *tgt, int err,
> - const struct bpf_map *map, u32 index),
> + enum xdp_redirect_type type,
> + const struct bpf_redirect_info *ri),
>
> - TP_ARGS(dev, xdp, tgt, err, map, index),
> + TP_ARGS(dev, xdp, tgt, err, type, ri),
>
> TP_STRUCT__entry(
> __field(int, prog_id)
> @@ -111,14 +107,30 @@ DECLARE_EVENT_CLASS(xdp_redirect_template,
> ),
>
> TP_fast_assign(
> + u32 ifindex = 0, map_id = 0, index = ri->tgt_index;
> +
> + switch (type) {
> + case XDP_REDIR_DEV_MAP:
> + ifindex = ((struct _bpf_dtab_netdev *)tgt)->dev->ifindex;
> + fallthrough;
> + case XDP_REDIR_CPU_MAP:
> + case XDP_REDIR_XSK_MAP:
> + map_id = ri->map_id;
> + break;
> + case XDP_REDIR_DEV_IFINDEX:
> + ifindex = (u32)(long)tgt;
> + break;
> + default:
> + break;
> + }
> +
> __entry->prog_id = xdp->aux->id;
> __entry->act = XDP_REDIRECT;
> __entry->ifindex = dev->ifindex;
> __entry->err = err;
> - __entry->to_ifindex = map ? devmap_ifindex(tgt, map) :
> - index;
> - __entry->map_id = map ? map->id : 0;
> - __entry->map_index = map ? index : 0;
> + __entry->to_ifindex = ifindex;
> + __entry->map_id = map_id;
> + __entry->map_index = index;
> ),
>
> TP_printk("prog_id=%d action=%s ifindex=%d to_ifindex=%d err=%d"
> @@ -133,45 +145,49 @@ DEFINE_EVENT(xdp_redirect_template, xdp_redirect,
> TP_PROTO(const struct net_device *dev,
> const struct bpf_prog *xdp,
> const void *tgt, int err,
> - const struct bpf_map *map, u32 index),
> - TP_ARGS(dev, xdp, tgt, err, map, index)
> + enum xdp_redirect_type type,
> + const struct bpf_redirect_info *ri),
> + TP_ARGS(dev, xdp, tgt, err, type, ri)
> );
>
> DEFINE_EVENT(xdp_redirect_template, xdp_redirect_err,
> TP_PROTO(const struct net_device *dev,
> const struct bpf_prog *xdp,
> const void *tgt, int err,
> - const struct bpf_map *map, u32 index),
> - TP_ARGS(dev, xdp, tgt, err, map, index)
> + enum xdp_redirect_type type,
> + const struct bpf_redirect_info *ri),
> + TP_ARGS(dev, xdp, tgt, err, type, ri)
> );
>
> #define _trace_xdp_redirect(dev, xdp, to) \
> - trace_xdp_redirect(dev, xdp, NULL, 0, NULL, to)
> + trace_xdp_redirect(dev, xdp, NULL, 0, XDP_REDIR_DEV_IFINDEX, NULL)
>
> #define _trace_xdp_redirect_err(dev, xdp, to, err) \
> - trace_xdp_redirect_err(dev, xdp, NULL, err, NULL, to)
> + trace_xdp_redirect_err(dev, xdp, NULL, err, XDP_REDIR_DEV_IFINDEX, NULL)
>
> -#define _trace_xdp_redirect_map(dev, xdp, to, map, index) \
> - trace_xdp_redirect(dev, xdp, to, 0, map, index)
> +#define _trace_xdp_redirect_map(dev, xdp, to, type, ri) \
> + trace_xdp_redirect(dev, xdp, to, 0, type, ri)
>
> -#define _trace_xdp_redirect_map_err(dev, xdp, to, map, index, err) \
> - trace_xdp_redirect_err(dev, xdp, to, err, map, index)
> +#define _trace_xdp_redirect_map_err(dev, xdp, to, type, ri, err) \
> + trace_xdp_redirect_err(dev, xdp, to, err, type, ri)
>
> /* not used anymore, but kept around so as not to break old programs */
> DEFINE_EVENT(xdp_redirect_template, xdp_redirect_map,
> TP_PROTO(const struct net_device *dev,
> const struct bpf_prog *xdp,
> const void *tgt, int err,
> - const struct bpf_map *map, u32 index),
> - TP_ARGS(dev, xdp, tgt, err, map, index)
> + enum xdp_redirect_type type,
> + const struct bpf_redirect_info *ri),
> + TP_ARGS(dev, xdp, tgt, err, type, ri)
> );
>
> DEFINE_EVENT(xdp_redirect_template, xdp_redirect_map_err,
> TP_PROTO(const struct net_device *dev,
> const struct bpf_prog *xdp,
> const void *tgt, int err,
> - const struct bpf_map *map, u32 index),
> - TP_ARGS(dev, xdp, tgt, err, map, index)
> + enum xdp_redirect_type type,
> + const struct bpf_redirect_info *ri),
> + TP_ARGS(dev, xdp, tgt, err, type, ri)
> );
>
> TRACE_EVENT(xdp_cpumap_kthread,
> diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c
> index a4d2cb93cd69..b7f4d22f5c8d 100644
> --- a/kernel/bpf/cpumap.c
> +++ b/kernel/bpf/cpumap.c
> @@ -543,7 +543,6 @@ static void cpu_map_free(struct bpf_map *map)
> * complete.
> */
>
> - bpf_clear_redirect_map(map);
> synchronize_rcu();
>
> /* For cpu_map the remote CPUs can still be using the entries
> diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
> index 37ac4cde9713..b5681a98020d 100644
> --- a/kernel/bpf/devmap.c
> +++ b/kernel/bpf/devmap.c
> @@ -197,7 +197,6 @@ static void dev_map_free(struct bpf_map *map)
> list_del_rcu(&dtab->list);
> spin_unlock(&dev_map_lock);
>
> - bpf_clear_redirect_map(map);
> synchronize_rcu();
>
> /* Make sure prior __dev_map_entry_free() have completed. */
> diff --git a/net/core/filter.c b/net/core/filter.c
> index fd64d768e16a..56074b88d7e2 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -3919,23 +3919,6 @@ static const struct bpf_func_proto bpf_xdp_adjust_meta_proto = {
> .arg2_type = ARG_ANYTHING,
> };
>
> -static int __bpf_tx_xdp_map(struct net_device *dev_rx, void *fwd,
> - struct bpf_map *map, struct xdp_buff *xdp)
> -{
> - switch (map->map_type) {
> - case BPF_MAP_TYPE_DEVMAP:
> - case BPF_MAP_TYPE_DEVMAP_HASH:
> - return dev_map_enqueue(fwd, xdp, dev_rx);
> - case BPF_MAP_TYPE_CPUMAP:
> - return cpu_map_enqueue(fwd, xdp, dev_rx);
> - case BPF_MAP_TYPE_XSKMAP:
> - return __xsk_map_redirect(fwd, xdp);
> - default:
> - return -EBADRQC;
> - }
> - return 0;
> -}
> -
> void xdp_do_flush(void)
> {
> __dev_flush();
> @@ -3944,55 +3927,45 @@ void xdp_do_flush(void)
> }
> EXPORT_SYMBOL_GPL(xdp_do_flush);
>
> -void bpf_clear_redirect_map(struct bpf_map *map)
> -{
> - struct bpf_redirect_info *ri;
> - int cpu;
> -
> - for_each_possible_cpu(cpu) {
> - ri = per_cpu_ptr(&bpf_redirect_info, cpu);
> - /* Avoid polluting remote cacheline due to writes if
> - * not needed. Once we pass this test, we need the
> - * cmpxchg() to make sure it hasn't been changed in
> - * the meantime by remote CPU.
> - */
> - if (unlikely(READ_ONCE(ri->map) == map))
> - cmpxchg(&ri->map, map, NULL);
> - }
> -}
> -
> int xdp_do_redirect(struct net_device *dev, struct xdp_buff *xdp,
> struct bpf_prog *xdp_prog)
> {
> struct bpf_redirect_info *ri = this_cpu_ptr(&bpf_redirect_info);
> - struct bpf_map *map = READ_ONCE(ri->map);
> - u32 index = ri->tgt_index;
> + enum xdp_redirect_type type = ri->tgt_type;
> void *fwd = ri->tgt_value;
> int err;
>
> - ri->tgt_index = 0;
> - ri->tgt_value = NULL;
> - WRITE_ONCE(ri->map, NULL);
> + ri->tgt_type = XDP_REDIR_UNSET;
>
> - if (unlikely(!map)) {
> - fwd = dev_get_by_index_rcu(dev_net(dev), index);
> + switch (type) {
> + case XDP_REDIR_DEV_IFINDEX:
> + fwd = dev_get_by_index_rcu(dev_net(dev), (u32)(long)fwd);
> if (unlikely(!fwd)) {
> err = -EINVAL;
> - goto err;
> + break;
> }
> -
> err = dev_xdp_enqueue(fwd, xdp, dev);
> - } else {
> - err = __bpf_tx_xdp_map(dev, fwd, map, xdp);
> + break;
> + case XDP_REDIR_DEV_MAP:
> + err = dev_map_enqueue(fwd, xdp, dev);
> + break;
> + case XDP_REDIR_CPU_MAP:
> + err = cpu_map_enqueue(fwd, xdp, dev);
> + break;
> + case XDP_REDIR_XSK_MAP:
> + err = __xsk_map_redirect(fwd, xdp);
> + break;
> + default:
> + err = -EBADRQC;
> }
>
> if (unlikely(err))
> goto err;
>
> - _trace_xdp_redirect_map(dev, xdp_prog, fwd, map, index);
> + _trace_xdp_redirect_map(dev, xdp_prog, fwd, type, ri);
> return 0;
> err:
> - _trace_xdp_redirect_map_err(dev, xdp_prog, fwd, map, index, err);
> + _trace_xdp_redirect_map_err(dev, xdp_prog, fwd, type, ri, err);
> return err;
> }
> EXPORT_SYMBOL_GPL(xdp_do_redirect);
> @@ -4001,41 +3974,40 @@ static int xdp_do_generic_redirect_map(struct net_device *dev,
> struct sk_buff *skb,
> struct xdp_buff *xdp,
> struct bpf_prog *xdp_prog,
> - struct bpf_map *map)
> + void *fwd,
> + enum xdp_redirect_type type)
> {
> struct bpf_redirect_info *ri = this_cpu_ptr(&bpf_redirect_info);
> - u32 index = ri->tgt_index;
> - void *fwd = ri->tgt_value;
> - int err = 0;
> -
> - ri->tgt_index = 0;
> - ri->tgt_value = NULL;
> - WRITE_ONCE(ri->map, NULL);
> + int err;
>
> - if (map->map_type == BPF_MAP_TYPE_DEVMAP ||
> - map->map_type == BPF_MAP_TYPE_DEVMAP_HASH) {
> + switch (type) {
> + case XDP_REDIR_DEV_MAP: {
> struct bpf_dtab_netdev *dst = fwd;
I thought the braces around the case body looked a bit odd. I guess
that's to get a local scope for the dst var (and xs var below), right?
This is basically a cast, though, so I wonder if you couldn't just as
well use the fwd pointer directly (with a cast) in the function call
below? WDYT?
(Strictly speaking I don't think the compiler will even complain if you
omit the cast as well, but having it in there is nice fore readability I
think, and guards against someone forgetting to update the call if the
function prototype changes).
> err = dev_map_generic_redirect(dst, skb, xdp_prog);
> if (unlikely(err))
> goto err;
> - } else if (map->map_type == BPF_MAP_TYPE_XSKMAP) {
> + break;
> + }
> + case XDP_REDIR_XSK_MAP: {
> struct xdp_sock *xs = fwd;
>
> err = xsk_generic_rcv(xs, xdp);
> if (err)
> goto err;
> consume_skb(skb);
> - } else {
> + break;
> + }
> + default:
> /* TODO: Handle BPF_MAP_TYPE_CPUMAP */
> err = -EBADRQC;
> goto err;
> }
>
> - _trace_xdp_redirect_map(dev, xdp_prog, fwd, map, index);
> + _trace_xdp_redirect_map(dev, xdp_prog, fwd, type, ri);
> return 0;
> err:
> - _trace_xdp_redirect_map_err(dev, xdp_prog, fwd, map, index, err);
> + _trace_xdp_redirect_map_err(dev, xdp_prog, fwd, type, ri, err);
> return err;
> }
>
> @@ -4043,29 +4015,31 @@ int xdp_do_generic_redirect(struct net_device *dev, struct sk_buff *skb,
> struct xdp_buff *xdp, struct bpf_prog *xdp_prog)
> {
> struct bpf_redirect_info *ri = this_cpu_ptr(&bpf_redirect_info);
> - struct bpf_map *map = READ_ONCE(ri->map);
> - u32 index = ri->tgt_index;
> - struct net_device *fwd;
> + enum xdp_redirect_type type = ri->tgt_type;
> + void *fwd = ri->tgt_value;
> int err = 0;
>
> - if (map)
> - return xdp_do_generic_redirect_map(dev, skb, xdp, xdp_prog,
> - map);
> - ri->tgt_index = 0;
> - fwd = dev_get_by_index_rcu(dev_net(dev), index);
> - if (unlikely(!fwd)) {
> - err = -EINVAL;
> - goto err;
> - }
> + ri->tgt_type = XDP_REDIR_UNSET;
> + ri->tgt_value = NULL;
>
> - err = xdp_ok_fwd_dev(fwd, skb->len);
> - if (unlikely(err))
> - goto err;
> + if (type == XDP_REDIR_DEV_IFINDEX) {
> + fwd = dev_get_by_index_rcu(dev_net(dev), (u32)(long)fwd);
> + if (unlikely(!fwd)) {
> + err = -EINVAL;
> + goto err;
> + }
>
> - skb->dev = fwd;
> - _trace_xdp_redirect(dev, xdp_prog, index);
> - generic_xdp_tx(skb, xdp_prog);
> - return 0;
> + err = xdp_ok_fwd_dev(fwd, skb->len);
> + if (unlikely(err))
> + goto err;
> +
> + skb->dev = fwd;
> + _trace_xdp_redirect(dev, xdp_prog, index);
> + generic_xdp_tx(skb, xdp_prog);
> + return 0;
> + }
> +
> + return xdp_do_generic_redirect_map(dev, skb, xdp, xdp_prog, fwd, type);
> err:
> _trace_xdp_redirect_err(dev, xdp_prog, index, err);
> return err;
> @@ -4078,10 +4052,9 @@ BPF_CALL_2(bpf_xdp_redirect, u32, ifindex, u64, flags)
> if (unlikely(flags))
> return XDP_ABORTED;
>
> - ri->flags = flags;
> - ri->tgt_index = ifindex;
> - ri->tgt_value = NULL;
> - WRITE_ONCE(ri->map, NULL);
> + ri->tgt_type = XDP_REDIR_DEV_IFINDEX;
> + ri->tgt_index = 0;
> + ri->tgt_value = (void *)(long)ifindex;
>
> return XDP_REDIRECT;
> }
> @@ -4096,7 +4069,8 @@ static const struct bpf_func_proto bpf_xdp_redirect_proto = {
>
> static __always_inline s64 __bpf_xdp_redirect_map(struct bpf_map *map, u32 ifindex, u64 flags,
> void *lookup_elem(struct bpf_map *map,
> - u32 key))
> + u32 key),
> + enum xdp_redirect_type type)
> {
> struct bpf_redirect_info *ri = this_cpu_ptr(&bpf_redirect_info);
>
> @@ -4105,35 +4079,39 @@ static __always_inline s64 __bpf_xdp_redirect_map(struct bpf_map *map, u32 ifind
>
> ri->tgt_value = lookup_elem(map, ifindex);
> if (unlikely(!ri->tgt_value)) {
> - WRITE_ONCE(ri->map, NULL);
> + ri->tgt_type = XDP_REDIR_UNSET;
> return flags;
> }
>
> - ri->flags = flags;
> ri->tgt_index = ifindex;
> - WRITE_ONCE(ri->map, map);
> + ri->tgt_type = type;
> + ri->map_id = map->id;
>
> return XDP_REDIRECT;
> }
>
> BPF_CALL_3(bpf_xdp_redirect_devmap, struct bpf_map *, map, u32, ifindex, u64, flags)
> {
> - return __bpf_xdp_redirect_map(map, ifindex, flags, __dev_map_lookup_elem);
> + return __bpf_xdp_redirect_map(map, ifindex, flags, __dev_map_lookup_elem,
> + XDP_REDIR_DEV_MAP);
> }
>
> BPF_CALL_3(bpf_xdp_redirect_devmap_hash, struct bpf_map *, map, u32, ifindex, u64, flags)
> {
> - return __bpf_xdp_redirect_map(map, ifindex, flags, __dev_map_hash_lookup_elem);
> + return __bpf_xdp_redirect_map(map, ifindex, flags, __dev_map_hash_lookup_elem,
> + XDP_REDIR_DEV_MAP);
> }
>
> BPF_CALL_3(bpf_xdp_redirect_cpumap, struct bpf_map *, map, u32, ifindex, u64, flags)
> {
> - return __bpf_xdp_redirect_map(map, ifindex, flags, __cpu_map_lookup_elem);
> + return __bpf_xdp_redirect_map(map, ifindex, flags, __cpu_map_lookup_elem,
> + XDP_REDIR_CPU_MAP);
> }
>
> BPF_CALL_3(bpf_xdp_redirect_xskmap, struct bpf_map *, map, u32, ifindex, u64, flags)
> {
> - return __bpf_xdp_redirect_map(map, ifindex, flags, __xsk_map_lookup_elem);
> + return __bpf_xdp_redirect_map(map, ifindex, flags, __xsk_map_lookup_elem,
> + XDP_REDIR_XSK_MAP);
> }
>
> bpf_func_proto_func get_xdp_redirect_func(enum bpf_map_type map_type)
> diff --git a/net/xdp/xskmap.c b/net/xdp/xskmap.c
> index 113fd9017203..c285d3dd04ad 100644
> --- a/net/xdp/xskmap.c
> +++ b/net/xdp/xskmap.c
> @@ -87,7 +87,6 @@ static void xsk_map_free(struct bpf_map *map)
> {
> struct xsk_map *m = container_of(map, struct xsk_map, map);
>
> - bpf_clear_redirect_map(map);
> synchronize_net();
> bpf_map_area_free(m);
> }
> --
> 2.27.0
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