Merge branch 'bpf-ring-buffer'

Andrii Nakryiko says:

====================
Implement a new BPF ring buffer, as presented at BPF virtual conference ([0]).
It presents an alternative to perf buffer, following its semantics closely,
but allowing sharing same instance of ring buffer across multiple CPUs
efficiently.

Most patches have extensive commentary explaining various aspects, so I'll
keep cover letter short. Overall structure of the patch set:
- patch #1 adds BPF ring buffer implementation to kernel and necessary
  verifier support;
- patch #2 adds libbpf consumer implementation for BPF ringbuf;
- patch #3 adds selftest, both for single BPF ring buf use case, as well as
  using it with array/hash of maps;
- patch #4 adds extensive benchmarks and provide some analysis in commit
  message, it builds upon selftests/bpf's bench runner.
- patch #5 adds most of patch #1 commit message as a doc under
  Documentation/bpf/ringbuf.rst.

Litmus tests, validating consumer/producer protocols and memory orderings,
were moved out as discussed in [1] and are going to be posted against -rcu
tree and put under Documentation/litmus-tests/bpf-rb.

  [0] https://docs.google.com/presentation/d/18ITdg77Bj6YDOH2LghxrnFxiPWe0fAqcmJY95t_qr0w
  [1] https://lkml.org/lkml/2020/5/22/1011

v3->v4:
- fix ringbuf freeing (vunmap, __free_page); verified with a trivial loop
  creating and closing ringbuf map endlessly (Daniel);

v2->v3:
- dropped unnecessary smp_wmb() (Paul);
- verifier reference type enhancement patch was dropped (Alexei);
- better verifier message for various memory access checks (Alexei);
- clarified a bit roundup_len() bit shifting (Alexei);
- converted doc to .rst (Alexei);
- fixed warning on 32-bit arches regarding tautological ring area size check.

v1->v2:
- commit()/discard()/output() accept flags (NO_WAKEUP/FORCE_WAKEUP) (Stanislav);
- bpf_ringbuf_query() added, returning available data size, ringbuf size,
  consumer/producer positions, needed to implement smarter notification policy
  (Stanislav);
- added ringbuf UAPI constants to include/uapi/linux/bpf.h (Jonathan);
- fixed sample size check, added proper ringbuf size check (Jonathan, Alexei);
- wake_up_all() is done through irq_work (Alexei);
- consistent use of smp_load_acquire/smp_store_release, no
  READ_ONCE/WRITE_ONCE (Alexei);
- added Documentation/bpf/ringbuf.txt (Stanislav);
- updated litmus test with smp_load_acquire/smp_store_release changes;
- added ring_buffer__consume() API to libbpf for busy-polling;
- ring_buffer__poll() on success returns number of records consumed;
- fixed EPOLL notifications, don't assume available data, done similarly to
  perfbuf's implementation;
- both ringbuf and perfbuf now have --rb-sampled mode, instead of
  pb-raw/pb-custom mode, updated benchmark results;
- extended ringbuf selftests to validate epoll logic/manual notification
  logic, as well as bpf_ringbuf_query().
====================

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

1 files changed, 83 insertions, 1 deletions

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 54b93f8b49b8..974ca6e948e3 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -147,6 +147,7 @@ enum bpf_map_type {
 	BPF_MAP_TYPE_SK_STORAGE,
 	BPF_MAP_TYPE_DEVMAP_HASH,
 	BPF_MAP_TYPE_STRUCT_OPS,
+	BPF_MAP_TYPE_RINGBUF,
 };
 
 /* Note that tracing related programs such as
@@ -3157,6 +3158,59 @@ union bpf_attr {
  *		**bpf_sk_cgroup_id**\ ().
  *	Return
  *		The id is returned or 0 in case the id could not be retrieved.
+ *
+ * void *bpf_ringbuf_output(void *ringbuf, void *data, u64 size, u64 flags)
+ * 	Description
+ * 		Copy *size* bytes from *data* into a ring buffer *ringbuf*.
+ * 		If BPF_RB_NO_WAKEUP is specified in *flags*, no notification of
+ * 		new data availability is sent.
+ * 		IF BPF_RB_FORCE_WAKEUP is specified in *flags*, notification of
+ * 		new data availability is sent unconditionally.
+ * 	Return
+ * 		0, on success;
+ * 		< 0, on error.
+ *
+ * void *bpf_ringbuf_reserve(void *ringbuf, u64 size, u64 flags)
+ * 	Description
+ * 		Reserve *size* bytes of payload in a ring buffer *ringbuf*.
+ * 	Return
+ * 		Valid pointer with *size* bytes of memory available; NULL,
+ * 		otherwise.
+ *
+ * void bpf_ringbuf_submit(void *data, u64 flags)
+ * 	Description
+ * 		Submit reserved ring buffer sample, pointed to by *data*.
+ * 		If BPF_RB_NO_WAKEUP is specified in *flags*, no notification of
+ * 		new data availability is sent.
+ * 		IF BPF_RB_FORCE_WAKEUP is specified in *flags*, notification of
+ * 		new data availability is sent unconditionally.
+ * 	Return
+ * 		Nothing. Always succeeds.
+ *
+ * void bpf_ringbuf_discard(void *data, u64 flags)
+ * 	Description
+ * 		Discard reserved ring buffer sample, pointed to by *data*.
+ * 		If BPF_RB_NO_WAKEUP is specified in *flags*, no notification of
+ * 		new data availability is sent.
+ * 		IF BPF_RB_FORCE_WAKEUP is specified in *flags*, notification of
+ * 		new data availability is sent unconditionally.
+ * 	Return
+ * 		Nothing. Always succeeds.
+ *
+ * u64 bpf_ringbuf_query(void *ringbuf, u64 flags)
+ *	Description
+ *		Query various characteristics of provided ring buffer. What
+ *		exactly is queries is determined by *flags*:
+ *		  - BPF_RB_AVAIL_DATA - amount of data not yet consumed;
+ *		  - BPF_RB_RING_SIZE - the size of ring buffer;
+ *		  - BPF_RB_CONS_POS - consumer position (can wrap around);
+ *		  - BPF_RB_PROD_POS - producer(s) position (can wrap around);
+ *		Data returned is just a momentary snapshots of actual values
+ *		and could be inaccurate, so this facility should be used to
+ *		power heuristics and for reporting, not to make 100% correct
+ *		calculation.
+ *	Return
+ *		Requested value, or 0, if flags are not recognized.
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -3288,7 +3342,12 @@ union bpf_attr {
 	FN(seq_printf),			\
 	FN(seq_write),			\
 	FN(sk_cgroup_id),		\
-	FN(sk_ancestor_cgroup_id),
+	FN(sk_ancestor_cgroup_id),	\
+	FN(ringbuf_output),		\
+	FN(ringbuf_reserve),		\
+	FN(ringbuf_submit),		\
+	FN(ringbuf_discard),		\
+	FN(ringbuf_query),
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
  * function eBPF program intends to call
@@ -3398,6 +3457,29 @@ enum {
 	BPF_F_GET_BRANCH_RECORDS_SIZE	= (1ULL << 0),
 };
 
+/* BPF_FUNC_bpf_ringbuf_commit, BPF_FUNC_bpf_ringbuf_discard, and
+ * BPF_FUNC_bpf_ringbuf_output flags.
+ */
+enum {
+	BPF_RB_NO_WAKEUP		= (1ULL << 0),
+	BPF_RB_FORCE_WAKEUP		= (1ULL << 1),
+};
+
+/* BPF_FUNC_bpf_ringbuf_query flags */
+enum {
+	BPF_RB_AVAIL_DATA = 0,
+	BPF_RB_RING_SIZE = 1,
+	BPF_RB_CONS_POS = 2,
+	BPF_RB_PROD_POS = 3,
+};
+
+/* BPF ring buffer constants */
+enum {
+	BPF_RINGBUF_BUSY_BIT		= (1U << 31),
+	BPF_RINGBUF_DISCARD_BIT		= (1U << 30),
+	BPF_RINGBUF_HDR_SZ		= 8,
+};
+
 /* Mode for BPF_FUNC_skb_adjust_room helper. */
 enum bpf_adj_room_mode {
 	BPF_ADJ_ROOM_NET,