s390/bpf: fix stack allocation

On s390x we have to provide 160 bytes stack space before we can call
the next function. From the 160 bytes that we got from the previous
function we only use 11 * 8 bytes and have 160 - 11 * 8 bytes left.
Currently for BPF we allocate additional 160 - 11 * 8 bytes for the
next function. This is wrong because then the next function only gets:

 (160 - 11 * 8) + (160 - 11 * 8) = 2 * 72 = 144 bytes

Fix this and allocate enough memory for the next function.

Fixes: 054623105728 ("s390/bpf: Add s390x eBPF JIT compiler backend")
Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Acked-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

arch/s390/net/bpf_jit.h

@@ -48,7 +48,9 @@ extern u8 sk_load_word[], sk_load_half[], sk_load_byte[];
  * We get 160 bytes stack space from calling function, but only use
  * 11 * 8 byte (old backchain + r15 - r6) for storing registers.
  */
-#define STK_OFF (MAX_BPF_STACK + 8 + 4 + 4 + (160 - 11 * 8))
+#define STK_SPACE	(MAX_BPF_STACK + 8 + 4 + 4 + 160)
+#define STK_160_UNUSED	(160 - 11 * 8)
+#define STK_OFF		(STK_SPACE - 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 */