libeth: xdp: add XDP_TX buffers sending

Start adding XDP-specific code to libeth, namely handling XDP_TX buffers
(only sending).
The idea is that we accumulate up to 16 buffers on the stack, then,
if either the limit is reached or the polling is finished, flush them
at once with only one XDPSQ cleaning (if needed). The main sending
function will be aware of the sending budget and already have all the
info to send the buffers, so it can't fail.
Drivers need to provide 2 inline callbacks to the main sending function:
for cleaning an XDPSQ and for filling descriptors; the library code
takes care of the rest.
Note that unlike the generic code, multi-buffer support is not wrapped
here with unlikely() to not hurt header split setups.

&libeth_xdp_buff is a simple extension over &xdp_buff which has a direct
pointer to the corresponding Rx descriptor (and, luckily, precisely 1 CL
size and 16-byte alignment on x86_64).

Suggested-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com> # xmit logic
Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

3 files changed, 102 insertions, 3 deletions

diff --git a/drivers/net/ethernet/intel/libeth/Kconfig b/drivers/net/ethernet/intel/libeth/Kconfig
index 480293b71dbc..d8c4926574fb 100644
--- a/drivers/net/ethernet/intel/libeth/Kconfig
+++ b/drivers/net/ethernet/intel/libeth/Kconfig
@@ -1,9 +1,15 @@
 # SPDX-License-Identifier: GPL-2.0-only
-# Copyright (C) 2024 Intel Corporation
+# Copyright (C) 2024-2025 Intel Corporation
 
 config LIBETH
-	tristate
+	tristate "Common Ethernet library (libeth)" if COMPILE_TEST
 	select PAGE_POOL
 	help
 	  libeth is a common library containing routines shared between several
 	  drivers, but not yet promoted to the generic kernel API.
+
+config LIBETH_XDP
+	tristate "Common XDP library (libeth_xdp)" if COMPILE_TEST
+	select LIBETH
+	help
+	  XDP helpers based on libeth hotpath management.
diff --git a/drivers/net/ethernet/intel/libeth/Makefile b/drivers/net/ethernet/intel/libeth/Makefile
index 52492b081132..9ba78f463f2e 100644
--- a/drivers/net/ethernet/intel/libeth/Makefile
+++ b/drivers/net/ethernet/intel/libeth/Makefile
@@ -1,6 +1,10 @@
 # SPDX-License-Identifier: GPL-2.0-only
-# Copyright (C) 2024 Intel Corporation
+# Copyright (C) 2024-2025 Intel Corporation
 
 obj-$(CONFIG_LIBETH)		+= libeth.o
 
 libeth-y			:= rx.o
+
+obj-$(CONFIG_LIBETH_XDP)	+= libeth_xdp.o
+
+libeth_xdp-y			+= xdp.o
diff --git a/drivers/net/ethernet/intel/libeth/xdp.c b/drivers/net/ethernet/intel/libeth/xdp.c
new file mode 100644
index 000000000000..444449c72221
--- /dev/null
+++ b/drivers/net/ethernet/intel/libeth/xdp.c
@@ -0,0 +1,89 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright (C) 2025 Intel Corporation */
+
+#define DEFAULT_SYMBOL_NAMESPACE	"LIBETH_XDP"
+
+#include <linux/export.h>
+
+#include <net/libeth/xdp.h>
+
+/* ``XDP_TX`` bulking */
+
+static void __cold
+libeth_xdp_tx_return_one(const struct libeth_xdp_tx_frame *frm)
+{
+	if (frm->len_fl & LIBETH_XDP_TX_MULTI)
+		libeth_xdp_return_frags(frm->data + frm->soff, true);
+
+	libeth_xdp_return_va(frm->data, true);
+}
+
+static void __cold
+libeth_xdp_tx_return_bulk(const struct libeth_xdp_tx_frame *bq, u32 count)
+{
+	for (u32 i = 0; i < count; i++) {
+		const struct libeth_xdp_tx_frame *frm = &bq[i];
+
+		if (!(frm->len_fl & LIBETH_XDP_TX_FIRST))
+			continue;
+
+		libeth_xdp_tx_return_one(frm);
+	}
+}
+
+static void __cold libeth_trace_xdp_exception(const struct net_device *dev,
+					      const struct bpf_prog *prog,
+					      u32 act)
+{
+	trace_xdp_exception(dev, prog, act);
+}
+
+/**
+ * libeth_xdp_tx_exception - handle Tx exceptions of XDP frames
+ * @bq: XDP Tx frame bulk
+ * @sent: number of frames sent successfully (from this bulk)
+ * @flags: internal libeth_xdp flags
+ *
+ * Cold helper used by __libeth_xdp_tx_flush_bulk(), do not call directly.
+ * Reports XDP Tx exceptions, frees the frames that won't be sent or adjust
+ * the Tx bulk to try again later.
+ */
+void __cold libeth_xdp_tx_exception(struct libeth_xdp_tx_bulk *bq, u32 sent,
+				    u32 flags)
+{
+	const struct libeth_xdp_tx_frame *pos = &bq->bulk[sent];
+	u32 left = bq->count - sent;
+
+	libeth_trace_xdp_exception(bq->dev, bq->prog, XDP_TX);
+
+	if (!(flags & LIBETH_XDP_TX_DROP)) {
+		memmove(bq->bulk, pos, left * sizeof(*bq->bulk));
+		bq->count = left;
+
+		return;
+	}
+
+	libeth_xdp_tx_return_bulk(pos, left);
+
+	bq->count = 0;
+}
+EXPORT_SYMBOL_GPL(libeth_xdp_tx_exception);
+
+/* Rx polling path */
+
+/**
+ * libeth_xdp_return_buff_slow - free &libeth_xdp_buff
+ * @xdp: buffer to free/return
+ *
+ * Slowpath version of libeth_xdp_return_buff() to be called on exceptions,
+ * queue clean-ups etc., without unwanted inlining.
+ */
+void __cold libeth_xdp_return_buff_slow(struct libeth_xdp_buff *xdp)
+{
+	__libeth_xdp_return_buff(xdp, false);
+}
+EXPORT_SYMBOL_GPL(libeth_xdp_return_buff_slow);
+
+MODULE_DESCRIPTION("Common Ethernet library - XDP infra");
+MODULE_IMPORT_NS("LIBETH");
+MODULE_LICENSE("GPL");