s390/bpf: increase BPF_SIZE_MAX

Currently we have the restriction that jitted BPF programs can
have a maximum size of one page. The reason is that we use short
displacements for the literal pool.

The 20 bit displacements are available since z990 and BPF requires
z196 as minimum. Therefore we can remove this restriction and use
everywhere 20 bit signed long displacements.

Acked-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

arch/s390/net/bpf_jit_comp.c

@@ -45,7 +45,7 @@ struct bpf_jit {
 	int labels[1];		/* Labels for local jumps */
 };
 
-#define BPF_SIZE_MAX	4096	/* Max size for program */
+#define BPF_SIZE_MAX	0x7ffff	/* Max size for program (20 bit signed displ) */
 
 #define SEEN_SKB	1	/* skb access */
 #define SEEN_MEM	2	/* use mem[] for temporary storage */
@@ -203,15 +203,6 @@ static inline void reg_set_seen(struct bpf_jit *jit, u32 b1)
 	_EMIT6(op1 | __disp, op2);				\
 })
 
-#define EMIT6_DISP(op1, op2, b1, b2, b3, disp)			\
-({								\
-	_EMIT6_DISP(op1 | reg(b1, b2) << 16 |			\
-		    reg_high(b3) << 8, op2, disp);		\
-	REG_SET_SEEN(b1);					\
-	REG_SET_SEEN(b2);					\
-	REG_SET_SEEN(b3);					\
-})
-
 #define _EMIT6_DISP_LH(op1, op2, disp)				\
 ({								\
 	u32 _disp = (u32) disp;					\
@@ -981,8 +972,8 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp, int i
 		REG_SET_SEEN(BPF_REG_5);
 		jit->seen |= SEEN_FUNC;
 		/* lg %w1,<d(imm)>(%l) */
-		EMIT6_DISP(0xe3000000, 0x0004, REG_W1, REG_0, REG_L,
-			   EMIT_CONST_U64(func));
+		EMIT6_DISP_LH(0xe3000000, 0x0004, REG_W1, REG_0, REG_L,
+			      EMIT_CONST_U64(func));
 		/* basr %r14,%w1 */
 		EMIT2(0x0d00, REG_14, REG_W1);
 		/* lgr %b0,%r2: load return value into %b0 */