The XDP redirect process is two staged:
- bpf_prog_run_xdp() is invoked to run a eBPF program which inspects the
packet and makes decisions. While doing that, the per-CPU variable
bpf_redirect_info is used.
- Afterwards xdp_do_redirect() is invoked and accesses bpf_redirect_info
and it may also access other per-CPU variables like xskmap_flush_list.
At the very end of the NAPI callback, xdp_do_flush() is invoked which
does not access bpf_redirect_info but will touch the individual per-CPU
lists.
The per-CPU variables are only used in the NAPI callback hence disabling
bottom halves is the only protection mechanism. Users from preemptible
context (like cpu_map_kthread_run()) explicitly disable bottom halves
for protections reasons.
Without locking in local_bh_disable() on PREEMPT_RT this data structure
requires explicit locking.
PREEMPT_RT has forced-threaded interrupts enabled and every
NAPI-callback runs in a thread. If each thread has its own data
structure then locking can be avoided.
Create a struct bpf_net_context which contains struct bpf_redirect_info.
Define the variable on stack, use bpf_net_ctx_set() to save a pointer to
it. Use the __free() annotation to automatically reset the pointer once
function returns.
The bpf_net_ctx_set() may nest. For instance a function can be used from
within NET_RX_SOFTIRQ/ net_rx_action which uses bpf_net_ctx_set() and
NET_TX_SOFTIRQ which does not. Therefore only the first invocations
updates the pointer.
Use bpf_net_ctx_get_ri() as a wrapper to retrieve the current struct
bpf_redirect_info.
On PREEMPT_RT the pointer to bpf_net_context is saved task's
task_struct. On non-PREEMPT_RT builds the pointer saved in a per-CPU
variable (which is always NODE-local memory). Using always the
bpf_net_context approach has the advantage that there is almost zero
differences between PREEMPT_RT and non-PREEMPT_RT builds.
Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
Cc: Andrii Nakryiko <andrii@xxxxxxxxxx>
Cc: Eduard Zingerman <eddyz87@xxxxxxxxx>
Cc: Hao Luo <haoluo@xxxxxxxxxx>
Cc: Jesper Dangaard Brouer <hawk@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: John Fastabend <john.fastabend@xxxxxxxxx>
Cc: KP Singh <kpsingh@xxxxxxxxxx>
Cc: Martin KaFai Lau <martin.lau@xxxxxxxxx>
Cc: Song Liu <song@xxxxxxxxxx>
Cc: Stanislav Fomichev <sdf@xxxxxxxxxx>
Cc: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>
Cc: Yonghong Song <yonghong.song@xxxxxxxxx>
Cc: bpf@xxxxxxxxxxxxxxx
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
---
include/linux/filter.h | 42 ++++++++++++++++++++++++++++++++-----
include/linux/sched.h | 3 +++
kernel/bpf/cpumap.c | 3 +++
kernel/fork.c | 1 +
net/bpf/test_run.c | 11 +++++++++-
net/core/dev.c | 19 ++++++++++++++++-
net/core/filter.c | 47 +++++++++++++++++++-----------------------
net/core/lwt_bpf.c | 3 +++
8 files changed, 96 insertions(+), 33 deletions(-)
diff --git a/include/linux/filter.h b/include/linux/filter.h
index b02aea291b7e8..a0d0ea356f925 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -744,7 +744,39 @@ struct bpf_redirect_info {
struct bpf_nh_params nh;
};
-DECLARE_PER_CPU(struct bpf_redirect_info, bpf_redirect_info);
+struct bpf_net_context {
+ struct bpf_redirect_info ri;
+};
+
+static inline struct bpf_net_context *bpf_net_ctx_set(struct bpf_net_context *bpf_net_ctx)
+{
+ struct task_struct *tsk = current;
+
+ if (tsk->bpf_net_context != NULL)
+ return NULL;
+ tsk->bpf_net_context = bpf_net_ctx;
+ return bpf_net_ctx;
+}
+
+static inline void bpf_net_ctx_clear(struct bpf_net_context *bpf_net_ctx)
+{
+ if (bpf_net_ctx)
+ current->bpf_net_context = NULL;
+}
+
+static inline struct bpf_net_context *bpf_net_ctx_get(void)
+{
+ return current->bpf_net_context;
+}
+
+static inline struct bpf_redirect_info *bpf_net_ctx_get_ri(void)
+{
+ struct bpf_net_context *bpf_net_ctx = bpf_net_ctx_get();
+
+ return &bpf_net_ctx->ri;
+}
+
+DEFINE_FREE(bpf_net_ctx_clear, struct bpf_net_context *, bpf_net_ctx_clear(_T));
/* flags for bpf_redirect_info kern_flags */
#define BPF_RI_F_RF_NO_DIRECT BIT(0) /* no napi_direct on return_frame */
@@ -1022,21 +1054,21 @@ void bpf_clear_redirect_map(struct bpf_map *map);
static inline bool xdp_return_frame_no_direct(void)
{
- struct bpf_redirect_info *ri = this_cpu_ptr(&bpf_redirect_info);
+ struct bpf_redirect_info *ri = bpf_net_ctx_get_ri();
return ri->kern_flags & BPF_RI_F_RF_NO_DIRECT;
}
static inline void xdp_set_return_frame_no_direct(void)
{
- struct bpf_redirect_info *ri = this_cpu_ptr(&bpf_redirect_info);
+ struct bpf_redirect_info *ri = bpf_net_ctx_get_ri();
ri->kern_flags |= BPF_RI_F_RF_NO_DIRECT;
}
static inline void xdp_clear_return_frame_no_direct(void)
{
- struct bpf_redirect_info *ri = this_cpu_ptr(&bpf_redirect_info);
+ struct bpf_redirect_info *ri = bpf_net_ctx_get_ri();
ri->kern_flags &= ~BPF_RI_F_RF_NO_DIRECT;
}
@@ -1592,7 +1624,7 @@ static __always_inline long __bpf_xdp_redirect_map(struct bpf_map *map, u64 inde
u64 flags, const u64 flag_mask,
void *lookup_elem(struct bpf_map *map, u32 key))
{
- struct bpf_redirect_info *ri = this_cpu_ptr(&bpf_redirect_info);
+ struct bpf_redirect_info *ri = bpf_net_ctx_get_ri();
const u64 action_mask = XDP_ABORTED | XDP_DROP | XDP_PASS | XDP_TX;
/* Lower bits of the flags are used as return code on lookup failure */
diff --git a/include/linux/sched.h b/include/linux/sched.h
index a9b0ca72db55f..dfa1843ab2916 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -53,6 +53,7 @@ struct bio_list;
struct blk_plug;
struct bpf_local_storage;
struct bpf_run_ctx;
+struct bpf_net_context;
struct capture_control;
struct cfs_rq;
struct fs_struct;
@@ -1508,6 +1509,8 @@ struct task_struct {
/* Used for BPF run context */
struct bpf_run_ctx *bpf_ctx;
#endif
+ /* Used by BPF for per-TASK xdp storage */
+ struct bpf_net_context *bpf_net_context;
#ifdef CONFIG_GCC_PLUGIN_STACKLEAK
unsigned long lowest_stack;
diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c
index a8e34416e960f..66974bd027109 100644
--- a/kernel/bpf/cpumap.c
+++ b/kernel/bpf/cpumap.c
@@ -240,12 +240,14 @@ static int cpu_map_bpf_prog_run(struct bpf_cpu_map_entry *rcpu, void **frames,
int xdp_n, struct xdp_cpumap_stats *stats,
struct list_head *list)
{
+ struct bpf_net_context __bpf_net_ctx, *bpf_net_ctx;
int nframes;
if (!rcpu->prog)
return xdp_n;
rcu_read_lock_bh();
+ bpf_net_ctx = bpf_net_ctx_set(&__bpf_net_ctx);
nframes = cpu_map_bpf_prog_run_xdp(rcpu, frames, xdp_n, stats);
@@ -255,6 +257,7 @@ static int cpu_map_bpf_prog_run(struct bpf_cpu_map_entry *rcpu, void **frames,
if (unlikely(!list_empty(list)))
cpu_map_bpf_prog_run_skb(rcpu, list, stats);
+ bpf_net_ctx_clear(bpf_net_ctx);
rcu_read_unlock_bh(); /* resched point, may call do_softirq() */
return nframes;
diff --git a/kernel/fork.c b/kernel/fork.c
index 99076dbe27d83..f314bdd7e6108 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2355,6 +2355,7 @@ __latent_entropy struct task_struct *copy_process(
RCU_INIT_POINTER(p->bpf_storage, NULL);
p->bpf_ctx = NULL;
#endif
+ p->bpf_net_context = NULL;
/* Perform scheduler related setup. Assign this task to a CPU. */
retval = sched_fork(clone_flags, p);
diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
index f6aad4ed2ab2f..600cc8e428c1a 100644
--- a/net/bpf/test_run.c
+++ b/net/bpf/test_run.c
@@ -283,9 +283,10 @@ static int xdp_recv_frames(struct xdp_frame **frames, int nframes,
static int xdp_test_run_batch(struct xdp_test_data *xdp, struct bpf_prog *prog,
u32 repeat)
{
- struct bpf_redirect_info *ri = this_cpu_ptr(&bpf_redirect_info);
+ struct bpf_net_context __bpf_net_ctx, *bpf_net_ctx;
int err = 0, act, ret, i, nframes = 0, batch_sz;
struct xdp_frame **frames = xdp->frames;
+ struct bpf_redirect_info *ri;
struct xdp_page_head *head;
struct xdp_frame *frm;
bool redirect = false;
@@ -295,6 +296,8 @@ static int xdp_test_run_batch(struct xdp_test_data *xdp, struct bpf_prog *prog,
batch_sz = min_t(u32, repeat, xdp->batch_size);
local_bh_disable();
+ bpf_net_ctx = bpf_net_ctx_set(&__bpf_net_ctx);
+ ri = bpf_net_ctx_get_ri();
xdp_set_return_frame_no_direct();
for (i = 0; i < batch_sz; i++) {
@@ -359,6 +362,7 @@ static int xdp_test_run_batch(struct xdp_test_data *xdp, struct bpf_prog *prog,
}
xdp_clear_return_frame_no_direct();
+ bpf_net_ctx_clear(bpf_net_ctx);
local_bh_enable();
return err;
}
@@ -394,6 +398,7 @@ static int bpf_test_run_xdp_live(struct bpf_prog *prog, struct xdp_buff *ctx,
static int bpf_test_run(struct bpf_prog *prog, void *ctx, u32 repeat,
u32 *retval, u32 *time, bool xdp)
{
+ struct bpf_net_context __bpf_net_ctx, *bpf_net_ctx;
struct bpf_prog_array_item item = {.prog = prog};
struct bpf_run_ctx *old_ctx;
struct bpf_cg_run_ctx run_ctx;
@@ -419,10 +424,14 @@ static int bpf_test_run(struct bpf_prog *prog, void *ctx, u32 repeat,
do {
run_ctx.prog_item = &item;
local_bh_disable();
+ bpf_net_ctx = bpf_net_ctx_set(&__bpf_net_ctx);
+
if (xdp)
*retval = bpf_prog_run_xdp(prog, ctx);
else
*retval = bpf_prog_run(prog, ctx);
+
+ bpf_net_ctx_clear(bpf_net_ctx);
local_bh_enable();
} while (bpf_test_timer_continue(&t, 1, repeat, &ret, time));
bpf_reset_run_ctx(old_ctx);
diff --git a/net/core/dev.c b/net/core/dev.c
index 2c3f86c8cd176..3c0f5474eae78 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4030,11 +4030,15 @@ sch_handle_ingress(struct sk_buff *skb, struct packet_type **pt_prev, int *ret,
struct net_device *orig_dev, bool *another)
{
struct bpf_mprog_entry *entry = rcu_dereference_bh(skb->dev->tcx_ingress);
+ struct bpf_net_context *bpf_net_ctx __free(bpf_net_ctx_clear) = NULL;
enum skb_drop_reason drop_reason = SKB_DROP_REASON_TC_INGRESS;
+ struct bpf_net_context __bpf_net_ctx;
int sch_ret;
if (!entry)
return skb;
+
+ bpf_net_ctx = bpf_net_ctx_set(&__bpf_net_ctx);
if (*pt_prev) {
*ret = deliver_skb(skb, *pt_prev, orig_dev);
*pt_prev = NULL;
@@ -4085,13 +4089,17 @@ sch_handle_ingress(struct sk_buff *skb, struct packet_type **pt_prev, int *ret,
static __always_inline struct sk_buff *
sch_handle_egress(struct sk_buff *skb, int *ret, struct net_device *dev)
{
+ struct bpf_net_context *bpf_net_ctx __free(bpf_net_ctx_clear) = NULL;
struct bpf_mprog_entry *entry = rcu_dereference_bh(dev->tcx_egress);
enum skb_drop_reason drop_reason = SKB_DROP_REASON_TC_EGRESS;
+ struct bpf_net_context __bpf_net_ctx;
int sch_ret;
if (!entry)
return skb;
+ bpf_net_ctx = bpf_net_ctx_set(&__bpf_net_ctx);
+
/* qdisc_skb_cb(skb)->pkt_len & tcx_set_ingress() was
* already set by the caller.
*/
@@ -6356,13 +6364,15 @@ static void __napi_busy_loop(unsigned int napi_id,
bool (*loop_end)(void *, unsigned long),
void *loop_end_arg, unsigned flags, u16 budget)
{
+ struct bpf_net_context *bpf_net_ctx __free(bpf_net_ctx_clear) = NULL;
unsigned long start_time = loop_end ? busy_loop_current_time() : 0;
int (*napi_poll)(struct napi_struct *napi, int budget);
+ struct bpf_net_context __bpf_net_ctx;
void *have_poll_lock = NULL;
struct napi_struct *napi;
WARN_ON_ONCE(!rcu_read_lock_held());
-
+ bpf_net_ctx = bpf_net_ctx_set(&__bpf_net_ctx);
restart:
napi_poll = NULL;
@@ -6833,6 +6843,7 @@ static int napi_thread_wait(struct napi_struct *napi)
static void napi_threaded_poll_loop(struct napi_struct *napi)
{
+ struct bpf_net_context __bpf_net_ctx, *bpf_net_ctx;
struct softnet_data *sd;
unsigned long last_qs = jiffies;
@@ -6841,6 +6852,8 @@ static void napi_threaded_poll_loop(struct napi_struct *napi)
void *have;
local_bh_disable();
+ bpf_net_ctx = bpf_net_ctx_set(&__bpf_net_ctx);
+
sd = this_cpu_ptr(&softnet_data);
sd->in_napi_threaded_poll = true;
@@ -6856,6 +6869,7 @@ static void napi_threaded_poll_loop(struct napi_struct *napi)
net_rps_action_and_irq_enable(sd);
}
skb_defer_free_flush(sd);
+ bpf_net_ctx_clear(bpf_net_ctx);
local_bh_enable();
if (!repoll)
@@ -6878,13 +6892,16 @@ static int napi_threaded_poll(void *data)
static __latent_entropy void net_rx_action(struct softirq_action *h)
{
+ struct bpf_net_context *bpf_net_ctx __free(bpf_net_ctx_clear) = NULL;
struct softnet_data *sd = this_cpu_ptr(&softnet_data);
unsigned long time_limit = jiffies +
usecs_to_jiffies(READ_ONCE(net_hotdata.netdev_budget_usecs));
int budget = READ_ONCE(net_hotdata.netdev_budget);
+ struct bpf_net_context __bpf_net_ctx;
LIST_HEAD(list);
LIST_HEAD(repoll);
+ bpf_net_ctx = bpf_net_ctx_set(&__bpf_net_ctx);
start:
sd->in_net_rx_action = true;
local_irq_disable();
diff --git a/net/core/filter.c b/net/core/filter.c
index d6cf1a63c3f43..0a3cc71505b43 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -2475,9 +2475,6 @@ static const struct bpf_func_proto bpf_clone_redirect_proto = {
.arg3_type = ARG_ANYTHING,
};
-DEFINE_PER_CPU(struct bpf_redirect_info, bpf_redirect_info);
-EXPORT_PER_CPU_SYMBOL_GPL(bpf_redirect_info);
-
static struct net_device *skb_get_peer_dev(struct net_device *dev)
{
const struct net_device_ops *ops = dev->netdev_ops;
@@ -2490,7 +2487,7 @@ static struct net_device *skb_get_peer_dev(struct net_device *dev)
int skb_do_redirect(struct sk_buff *skb)
{
- struct bpf_redirect_info *ri = this_cpu_ptr(&bpf_redirect_info);
+ struct bpf_redirect_info *ri = bpf_net_ctx_get_ri();
struct net *net = dev_net(skb->dev);
struct net_device *dev;
u32 flags = ri->flags;
@@ -2523,7 +2520,7 @@ int skb_do_redirect(struct sk_buff *skb)
BPF_CALL_2(bpf_redirect, u32, ifindex, u64, flags)
{
- struct bpf_redirect_info *ri = this_cpu_ptr(&bpf_redirect_info);
+ struct bpf_redirect_info *ri = bpf_net_ctx_get_ri();
if (unlikely(flags & (~(BPF_F_INGRESS) | BPF_F_REDIRECT_INTERNAL)))
return TC_ACT_SHOT;
@@ -2544,7 +2541,7 @@ static const struct bpf_func_proto bpf_redirect_proto = {
BPF_CALL_2(bpf_redirect_peer, u32, ifindex, u64, flags)
{
- struct bpf_redirect_info *ri = this_cpu_ptr(&bpf_redirect_info);
+ struct bpf_redirect_info *ri = bpf_net_ctx_get_ri();
if (unlikely(flags))
return TC_ACT_SHOT;
@@ -2566,7 +2563,7 @@ static const struct bpf_func_proto bpf_redirect_peer_proto = {
BPF_CALL_4(bpf_redirect_neigh, u32, ifindex, struct bpf_redir_neigh *, params,
int, plen, u64, flags)
{
- struct bpf_redirect_info *ri = this_cpu_ptr(&bpf_redirect_info);
+ struct bpf_redirect_info *ri = bpf_net_ctx_get_ri();
if (unlikely((plen && plen < sizeof(*params)) || flags))
return TC_ACT_SHOT;
@@ -4294,19 +4291,17 @@ void xdp_do_check_flushed(struct napi_struct *napi)
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);
- }
+ /* ri->map is assigned in __bpf_xdp_redirect_map() from within a eBPF
+ * program/ during NAPI callback. It is used during
+ * xdp_do_generic_redirect_map()/ __xdp_do_redirect_frame() from the
+ * redirect callback afterwards. ri->map is cleared after usage.
+ * The path has no explicit RCU read section but the local_bh_disable()
+ * is also a RCU read section which makes the complete softirq callback
+ * RCU protected. This in turn makes ri->map RCU protected and it is
+ * sufficient to wait a grace period to ensure that no "ri->map == map"
+ * exists. dev_map_free() removes the map from the list and then
+ * invokes synchronize_rcu() after calling this function.
+ */
}
DEFINE_STATIC_KEY_FALSE(bpf_master_redirect_enabled_key);
@@ -4314,8 +4309,8 @@ EXPORT_SYMBOL_GPL(bpf_master_redirect_enabled_key);
u32 xdp_master_redirect(struct xdp_buff *xdp)
{
+ struct bpf_redirect_info *ri = bpf_net_ctx_get_ri();
struct net_device *master, *slave;
- struct bpf_redirect_info *ri = this_cpu_ptr(&bpf_redirect_info);
master = netdev_master_upper_dev_get_rcu(xdp->rxq->dev);
slave = master->netdev_ops->ndo_xdp_get_xmit_slave(master, xdp);
@@ -4432,7 +4427,7 @@ static __always_inline int __xdp_do_redirect_frame(struct bpf_redirect_info *ri,
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_redirect_info *ri = bpf_net_ctx_get_ri();
enum bpf_map_type map_type = ri->map_type;
if (map_type == BPF_MAP_TYPE_XSKMAP)
@@ -4446,7 +4441,7 @@ EXPORT_SYMBOL_GPL(xdp_do_redirect);
int xdp_do_redirect_frame(struct net_device *dev, struct xdp_buff *xdp,
struct xdp_frame *xdpf, struct bpf_prog *xdp_prog)
{
- struct bpf_redirect_info *ri = this_cpu_ptr(&bpf_redirect_info);
+ struct bpf_redirect_info *ri = bpf_net_ctx_get_ri();
enum bpf_map_type map_type = ri->map_type;
if (map_type == BPF_MAP_TYPE_XSKMAP)
@@ -4463,7 +4458,7 @@ static int xdp_do_generic_redirect_map(struct net_device *dev,
enum bpf_map_type map_type, u32 map_id,
u32 flags)
{
- struct bpf_redirect_info *ri = this_cpu_ptr(&bpf_redirect_info);
+ struct bpf_redirect_info *ri = bpf_net_ctx_get_ri();
struct bpf_map *map;
int err;
@@ -4517,7 +4512,7 @@ static int xdp_do_generic_redirect_map(struct net_device *dev,
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_redirect_info *ri = bpf_net_ctx_get_ri();
enum bpf_map_type map_type = ri->map_type;
void *fwd = ri->tgt_value;
u32 map_id = ri->map_id;
@@ -4553,7 +4548,7 @@ int xdp_do_generic_redirect(struct net_device *dev, struct sk_buff *skb,
BPF_CALL_2(bpf_xdp_redirect, u32, ifindex, u64, flags)
{
- struct bpf_redirect_info *ri = this_cpu_ptr(&bpf_redirect_info);
+ struct bpf_redirect_info *ri = bpf_net_ctx_get_ri();
if (unlikely(flags))
return XDP_ABORTED;
diff --git a/net/core/lwt_bpf.c b/net/core/lwt_bpf.c
index a94943681e5aa..afb05f58b64c5 100644
--- a/net/core/lwt_bpf.c
+++ b/net/core/lwt_bpf.c
@@ -38,12 +38,14 @@ static inline struct bpf_lwt *bpf_lwt_lwtunnel(struct lwtunnel_state *lwt)
static int run_lwt_bpf(struct sk_buff *skb, struct bpf_lwt_prog *lwt,
struct dst_entry *dst, bool can_redirect)
{
+ struct bpf_net_context __bpf_net_ctx, *bpf_net_ctx;
int ret;
/* Disabling BH is needed to protect per-CPU bpf_redirect_info between
* BPF prog and skb_do_redirect().
*/
local_bh_disable();
+ bpf_net_ctx = bpf_net_ctx_set(&__bpf_net_ctx);
bpf_compute_data_pointers(skb);
ret = bpf_prog_run_save_cb(lwt->prog, skb);
@@ -76,6 +78,7 @@ static int run_lwt_bpf(struct sk_buff *skb, struct bpf_lwt_prog *lwt,
break;
}
+ bpf_net_ctx_clear(bpf_net_ctx);
local_bh_enable();
return ret;
--
2.45.1
