selftests/xsk: Add support for zero copy testing

Introduce new mode to xdpxceiver responsible for testing AF_XDP zero
copy support of driver that serves underlying physical device. When
setting up test suite, determine whether driver has ZC support or not by
trying to bind XSK ZC socket to the interface. If it succeeded,
interpret it as ZC support being in place and do softirq and busy poll
tests for zero copy mode.

Note that Rx dropped tests are skipped since ZC path is not touching
rx_dropped stat at all.

Signed-off-by: Maciej Fijalkowski <[e-mail]>
Signed-off-by: Daniel Borkmann <[e-mail]>
Acked-by: Magnus Karlsson <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

tools/testing/selftests/bpf/xskxceiver.c

···
 }
 
 #define exit_with_error(error) __exit_with_error(error, __FILE__, __func__, __LINE__)
-
-#define mode_string(test) (test)->ifobj_tx->xdp_flags & XDP_FLAGS_SKB_MODE ? "SKB" : "DRV"
 #define busy_poll_string(test) (test)->ifobj_tx->busy_poll ? "BUSY-POLL " : ""
+static char *mode_string(struct test_spec *test)
+{
+	switch (test->mode) {
+	case TEST_MODE_SKB:
+		return "SKB";
+	case TEST_MODE_DRV:
+		return "DRV";
+	case TEST_MODE_ZC:
+		return "ZC";
+	default:
+		return "BOGUS";
+	}
+}
 
 static void report_failure(struct test_spec *test)
 {
···
 	return xsk_socket__create(&xsk->xsk, ifobject->ifname, 0, umem->umem, rxr, txr, &cfg);
 }
 
+static bool ifobj_zc_avail(struct ifobject *ifobject)
+{
+	size_t umem_sz = DEFAULT_UMEM_BUFFERS * XSK_UMEM__DEFAULT_FRAME_SIZE;
+	int mmap_flags = MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE;
+	struct xsk_socket_info *xsk;
+	struct xsk_umem_info *umem;
+	bool zc_avail = false;
+	void *bufs;
+	int ret;
+
+	bufs = mmap(NULL, umem_sz, PROT_READ | PROT_WRITE, mmap_flags, -1, 0);
+	if (bufs == MAP_FAILED)
+		exit_with_error(errno);
+
+	umem = calloc(1, sizeof(struct xsk_umem_info));
+	if (!umem) {
+		munmap(bufs, umem_sz);
+		exit_with_error(-ENOMEM);
+	}
+	umem->frame_size = XSK_UMEM__DEFAULT_FRAME_SIZE;
+	ret = xsk_configure_umem(umem, bufs, umem_sz);
+	if (ret)
+		exit_with_error(-ret);
+
+	xsk = calloc(1, sizeof(struct xsk_socket_info));
+	if (!xsk)
+		goto out;
+	ifobject->xdp_flags = XDP_FLAGS_UPDATE_IF_NOEXIST;
+	ifobject->xdp_flags |= XDP_FLAGS_DRV_MODE;
+	ifobject->bind_flags = XDP_USE_NEED_WAKEUP | XDP_ZEROCOPY;
+	ifobject->rx_on = true;
+	xsk->rxqsize = XSK_RING_CONS__DEFAULT_NUM_DESCS;
+	ret = __xsk_configure_socket(xsk, umem, ifobject, false);
+	if (!ret)
+		zc_avail = true;
+
+	xsk_socket__delete(xsk->xsk);
+	free(xsk);
+out:
+	munmap(umem->buffer, umem_sz);
+	xsk_umem__delete(umem->umem);
+	free(umem);
+	return zc_avail;
+}
+
 static struct option long_options[] = {
 	{"interface", required_argument, 0, 'i'},
 	{"busy-poll", no_argument, 0, 'b'},
···
 		else
 			ifobj->xdp_flags |= XDP_FLAGS_DRV_MODE;
 
-		ifobj->bind_flags = XDP_USE_NEED_WAKEUP | XDP_COPY;
+		ifobj->bind_flags = XDP_USE_NEED_WAKEUP;
+		if (mode == TEST_MODE_ZC)
+			ifobj->bind_flags |= XDP_ZEROCOPY;
+		else
+			ifobj->bind_flags |= XDP_COPY;
 	}
 
+	test->mode = mode;
 	__test_spec_init(test, ifobj_tx, ifobj_rx);
 }
 
···
 {
 	switch (type) {
 	case TEST_TYPE_STATS_RX_DROPPED:
+		if (mode == TEST_MODE_ZC) {
+			ksft_test_result_skip("Can not run RX_DROPPED test for ZC mode\n");
+			return;
+		}
 		testapp_stats_rx_dropped(test);
 		break;
 	case TEST_TYPE_STATS_TX_INVALID_DESCS:
···
 	init_iface(ifobj_rx, MAC2, MAC1, IP2, IP1, UDP_PORT2, UDP_PORT1,
 		   worker_testapp_validate_rx);
 
-	if (is_xdp_supported(ifobj_tx))
+	if (is_xdp_supported(ifobj_tx)) {
 		modes++;
+		if (ifobj_zc_avail(ifobj_tx))
+			modes++;
+	}
 
 	test_spec_init(&test, ifobj_tx, ifobj_rx, 0);
 	tx_pkt_stream_default = pkt_stream_generate(ifobj_tx->umem, DEFAULT_PKT_CNT, PKT_SIZE);

tools/testing/selftests/bpf/xskxceiver.h

···
 enum test_mode {
 	TEST_MODE_SKB,
 	TEST_MODE_DRV,
+	TEST_MODE_ZC,
 	TEST_MODE_MAX
 };
 
···
 	u16 current_step;
 	u16 nb_sockets;
 	bool fail;
+	enum test_mode mode;
 	char name[MAX_TEST_NAME_SIZE];
 };