selftests/xsk: Add new test case for AF_XDP under max ring sizes

Introduce a test case to evaluate AF_XDP's robustness by pushing hardware
and software ring sizes to their limits. This test ensures AF_XDP's
reliability amidst potential producer/consumer throttling due to maximum
ring utilization. The testing strategy includes:

1. Configuring rings to their maximum allowable sizes.
2. Executing a series of tests across diverse batch sizes to assess
   system's behavior under different configurations.
Signed-off-by: Tushar Vyavahare <tushar.vyavahare@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Magnus Karlsson <magnus.karlsson@intel.com>
Link: https://lore.kernel.org/bpf/20240402114529.545475-8-tushar.vyavahare@intel.com

tools/testing/selftests/bpf/xskxceiver.c

@@ -2439,6 +2439,30 @@ static int testapp_hw_sw_min_ring_size(struct test_spec *test)
 	return testapp_validate_traffic(test);
 }
 
+static int testapp_hw_sw_max_ring_size(struct test_spec *test)
+{
+	u32 max_descs = XSK_RING_PROD__DEFAULT_NUM_DESCS * 2;
+	int ret;
+
+	test->set_ring = true;
+	test->total_steps = 2;
+	test->ifobj_tx->ring.tx_pending = test->ifobj_tx->ring.tx_max_pending;
+	test->ifobj_tx->ring.rx_pending  = test->ifobj_tx->ring.rx_max_pending;
+	test->ifobj_rx->umem->num_frames = max_descs;
+	test->ifobj_rx->xsk->rxqsize = max_descs;
+	test->ifobj_tx->xsk->batch_size = XSK_RING_PROD__DEFAULT_NUM_DESCS;
+	test->ifobj_rx->xsk->batch_size = XSK_RING_PROD__DEFAULT_NUM_DESCS;
+
+	ret = testapp_validate_traffic(test);
+	if (ret)
+		return ret;
+
+	/* Set batch_size to 4095 */
+	test->ifobj_tx->xsk->batch_size = max_descs - 1;
+	test->ifobj_rx->xsk->batch_size = max_descs - 1;
+	return testapp_validate_traffic(test);
+}
+
 static void run_pkt_test(struct test_spec *test)
 {
 	int ret;
@@ -2544,6 +2568,7 @@ static const struct test_spec tests[] = {
 	{.name = "UNALIGNED_INV_DESC_MULTI_BUFF", .test_func = testapp_unaligned_inv_desc_mb},
 	{.name = "TOO_MANY_FRAGS", .test_func = testapp_too_many_frags},
 	{.name = "HW_SW_MIN_RING_SIZE", .test_func = testapp_hw_sw_min_ring_size},
+	{.name = "HW_SW_MAX_RING_SIZE", .test_func = testapp_hw_sw_max_ring_size},
 	};
 
 static void print_tests(void)