s390/bpf: take advantage of stack_depth tracking

Make use of the "stack_depth" tracking feature introduced with
commit 8726679a0f ("bpf: teach verifier to track stack depth") for the
s390 JIT, so that stack usage can be reduced.

Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>

arch/s390/net/bpf_jit.h

@@ -52,10 +52,13 @@ extern u8 sk_load_word[], sk_load_half[], sk_load_byte[];
  *
  * We get 160 bytes stack space from calling function, but only use
  * 12 * 8 byte for old backchain, r15..r6, and tail_call_cnt.
+ *
+ * The stack size used by the BPF program ("BPF stack" above) is passed
+ * via "aux->stack_depth".
  */
-#define STK_SPACE	(MAX_BPF_STACK + 8 + 8 + 4 + 4 + 160)
+#define STK_SPACE_ADD (8 + 8 + 4 + 4 + 160)
 #define STK_160_UNUSED	(160 - 12 * 8)
-#define STK_OFF		(STK_SPACE - STK_160_UNUSED)
+#define STK_OFF		(STK_SPACE_ADD - STK_160_UNUSED)
 #define STK_OFF_TMP	160	/* Offset of tmp buffer on stack */
 #define STK_OFF_HLEN	168	/* Offset of SKB header length on stack */
 #define STK_OFF_SKBP	176	/* Offset of SKB pointer on stack */