This commit introduces tracing infrastructure for AF_XDP sockets
(xsks) and a new trace event called 'xsk_packet_drop'. This trace
event is triggered when a packet cannot be processed by the socket
due to one of the following issues:
(1) packet exceeds the maximum permitted size.
(2) invalid fill descriptor address.
(3) invalid tx descriptor field.

The trace provides information about the error to the user. For
example the size vs permitted size is provided for (1). For (2)
and (3) the relevant descriptor fields are printed. This information
should help a user troubleshoot packet drops by providing this extra
level of detail which is not available through use of simple counters.

The tracepoint can be enabled/disabled by toggling
/sys/kernel/debug/tracing/events/xsk/xsk_packet_drop/enable

Signed-off-by: Ciara Loftus <redacted>
---
 MAINTAINERS                       |  1 +
 include/linux/bpf_trace.h         |  1 +
 include/trace/events/xsk.h        | 73 +++++++++++++++++++++++++++++++
 include/uapi/linux/if_xdp.h       |  6 +++
 kernel/bpf/core.c                 |  1 +
 net/xdp/xsk.c                     |  7 ++-
 net/xdp/xsk_buff_pool.c           |  3 ++
 net/xdp/xsk_queue.h               |  4 ++
 tools/include/uapi/linux/if_xdp.h |  6 +++
 9 files changed, 101 insertions(+), 1 deletion(-)
 create mode 100644 include/trace/events/xsk.h

diff --git a/MAINTAINERS b/MAINTAINERS
index 1df56a32d2df..efe6662d4198 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS

@@ -19440,6 +19440,7 @@ S:      Maintained
 F:     Documentation/networking/af_xdp.rst
 F:     include/net/xdp_sock*
 F:     include/net/xsk_buff_pool.h
+F:     include/trace/events/xsk.h
 F:     include/uapi/linux/if_xdp.h
 F:     include/uapi/linux/xdp_diag.h
 F:     include/net/netns/xdp.h

diff --git a/include/linux/bpf_trace.h b/include/linux/bpf_trace.h
index ddf896abcfb6..477d29b6c2c1 100644
--- a/include/linux/bpf_trace.h
+++ b/include/linux/bpf_trace.h

@@ -3,5 +3,6 @@
 #define __LINUX_BPF_TRACE_H__

 #include <trace/events/xdp.h>
+#include <trace/events/xsk.h>

 #endif /* __LINUX_BPF_TRACE_H__ */

diff --git a/include/trace/events/xsk.h b/include/trace/events/xsk.h
new file mode 100644
index 000000000000..e2984fad372c
--- /dev/null
+++ b/include/trace/events/xsk.h

@@ -0,0 +1,73 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright(c) 2021 Intel Corporation. */
+
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM xsk
+
+#if !defined(_TRACE_XSK_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_XSK_H
+
+#include <linux/if_xdp.h>
+#include <linux/tracepoint.h>
+
+#define print_reason(reason) \
+       __print_symbolic(reason, \
+                       { XSK_TRACE_DROP_PKT_TOO_BIG, "packet too big" }, \
+                       { XSK_TRACE_DROP_INVALID_FILLADDR, "invalid fill addr" }, \
+                       { XSK_TRACE_DROP_INVALID_TXD, "invalid tx desc" })
+
+#define print_val1(reason) \
+       __print_symbolic(reason, \
+                       { XSK_TRACE_DROP_PKT_TOO_BIG, "len" }, \
+                       { XSK_TRACE_DROP_INVALID_FILLADDR, "addr" }, \
+                       { XSK_TRACE_DROP_INVALID_TXD, "addr" })
+
+#define print_val2(reason) \
+       __print_symbolic(reason, \
+                       { XSK_TRACE_DROP_PKT_TOO_BIG, "max" }, \
+                       { XSK_TRACE_DROP_INVALID_FILLADDR, "not_used" }, \
+                       { XSK_TRACE_DROP_INVALID_TXD, "len" })
+
+#define print_val3(reason) \
+       __print_symbolic(reason, \
+                       { XSK_TRACE_DROP_PKT_TOO_BIG, "not_used" }, \
+                       { XSK_TRACE_DROP_INVALID_FILLADDR, "not_used" }, \
+                       { XSK_TRACE_DROP_INVALID_TXD, "options" })
+
+
+

+TRACE_EVENT(xsk_packet_drop,
+
+       TP_PROTO(char *name, u16 queue_id, u32 reason, u64 val1, u64 val2, u64 val3),
+
+       TP_ARGS(name, queue_id, reason, val1, val2, val3),
+
+       TP_STRUCT__entry(
+               __field(char *, name)
+               __field(u16, queue_id)
+               __field(u32, reason)
+               __field(u64, val1)
+               __field(u32, val2)
+               __field(u32, val3)
+       ),
+
+       TP_fast_assign(
+               __entry->name = name;
+               __entry->queue_id = queue_id;
+               __entry->reason = reason;
+               __entry->val1 = val1;
+               __entry->val2 = val2;
+               __entry->val3 = val3;
+       ),
+
+       TP_printk("netdev: %s qid %u reason: %s: %s %llu %s %u %s %u",
+                 __entry->name, __entry->queue_id, print_reason(__entry->reason),
+                 print_val1(__entry->reason), __entry->val1,
+                 print_val2(__entry->reason), __entry->val2,
+                 print_val3(__entry->reason), __entry->val3
+       )
+);
+
+#endif /* _TRACE_XSK_H */
+
+#include <trace/define_trace.h>

diff --git a/include/uapi/linux/if_xdp.h b/include/uapi/linux/if_xdp.h
index a78a8096f4ce..d7eb031d2465 100644
--- a/include/uapi/linux/if_xdp.h
+++ b/include/uapi/linux/if_xdp.h

@@ -108,4 +108,10 @@ struct xdp_desc {

 /* UMEM descriptor is __u64 */

+enum xdp_trace_reasons {