Revert "bpf, test_run: fix &xdp_frame misplacement for LIVE_FRAMES"

This reverts commit 6c20822f.

build bot failed on arch with different cache line size:
https://lore.kernel.org/bpf/50c35055-afa9-d01e-9a05-ea5351280e4f@intel.com/Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>

net/bpf/test_run.c

@@ -97,11 +97,8 @@ static bool bpf_test_timer_continue(struct bpf_test_timer *t, int iterations,
 struct xdp_page_head {
 	struct xdp_buff orig_ctx;
 	struct xdp_buff ctx;
-	union {
-		/* ::data_hard_start starts here */
-		DECLARE_FLEX_ARRAY(struct xdp_frame, frame);
-		DECLARE_FLEX_ARRAY(u8, data);
-	};
+	struct xdp_frame frm;
+	u8 data[];
 };
 
 struct xdp_test_data {
@@ -119,20 +116,6 @@ struct xdp_test_data {
 #define TEST_XDP_FRAME_SIZE (PAGE_SIZE - sizeof(struct xdp_page_head))
 #define TEST_XDP_MAX_BATCH 256
 
-#if BITS_PER_LONG == 64 && PAGE_SIZE == SZ_4K
-/* tools/testing/selftests/bpf/prog_tests/xdp_do_redirect.c:%MAX_PKT_SIZE
- * must be updated accordingly when any of these changes, otherwise BPF
- * selftests will fail.
- */
-#ifdef __s390x__
-#define TEST_MAX_PKT_SIZE 3216
-#else
-#define TEST_MAX_PKT_SIZE 3408
-#endif
-static_assert(SKB_WITH_OVERHEAD(TEST_XDP_FRAME_SIZE - XDP_PACKET_HEADROOM) ==
-	      TEST_MAX_PKT_SIZE);
-#endif
-
 static void xdp_test_run_init_page(struct page *page, void *arg)
 {
 	struct xdp_page_head *head = phys_to_virt(page_to_phys(page));
@@ -149,8 +132,8 @@ static void xdp_test_run_init_page(struct page *page, void *arg)
 	headroom -= meta_len;
 
 	new_ctx = &head->ctx;
-	frm = head->frame;
-	data = head->data;
+	frm = &head->frm;
+	data = &head->data;
 	memcpy(data + headroom, orig_ctx->data_meta, frm_len);
 
 	xdp_init_buff(new_ctx, TEST_XDP_FRAME_SIZE, &xdp->rxq);
@@ -240,7 +223,7 @@ static void reset_ctx(struct xdp_page_head *head)
 	head->ctx.data = head->orig_ctx.data;
 	head->ctx.data_meta = head->orig_ctx.data_meta;
 	head->ctx.data_end = head->orig_ctx.data_end;
-	xdp_update_frame_from_buff(&head->ctx, head->frame);
+	xdp_update_frame_from_buff(&head->ctx, &head->frm);
 }
 
 static int xdp_recv_frames(struct xdp_frame **frames, int nframes,
@@ -302,7 +285,7 @@ static int xdp_test_run_batch(struct xdp_test_data *xdp, struct bpf_prog *prog,
 		head = phys_to_virt(page_to_phys(page));
 		reset_ctx(head);
 		ctx = &head->ctx;
-		frm = head->frame;
+		frm = &head->frm;
 		xdp->frame_cnt++;
 
 		act = bpf_prog_run_xdp(prog, ctx);

tools/testing/selftests/bpf/prog_tests/xdp_do_redirect.c

@@ -65,13 +65,12 @@ static int attach_tc_prog(struct bpf_tc_hook *hook, int fd)
 }
 
 /* The maximum permissible size is: PAGE_SIZE - sizeof(struct xdp_page_head) -
- * SKB_DATA_ALIGN(sizeof(struct skb_shared_info)) - XDP_PACKET_HEADROOM =
- * 3408 bytes for 64-byte cacheline and 3216 for 256-byte one.
+ * sizeof(struct skb_shared_info) - XDP_PACKET_HEADROOM = 3368 bytes
  */
 #if defined(__s390x__)
-#define MAX_PKT_SIZE 3216
+#define MAX_PKT_SIZE 3176
 #else
-#define MAX_PKT_SIZE 3408
+#define MAX_PKT_SIZE 3368
 #endif
 static void test_max_pkt_size(int fd)
 {