From: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Date: Wed, 29 Jul 2015 19:15:17 +0000 (+0200)
Subject: s390/bpf: Only clear A and X for converted BPF programs
X-Git-Url: http://drtracing.org/?a=commitdiff_plain;h=cde66c2d88da1d73d755109c80ce4c34b917596b;p=deliverable%2Flinux.git

s390/bpf: Only clear A and X for converted BPF programs

Only classic BPF programs that have been converted to eBPF need to clear
the A and X registers. We can check for converted programs with:

  bpf_prog->type == BPF_PROG_TYPE_UNSPEC

So add the check and skip initialization for real eBPF programs.

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

diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
index 04af36728a18..3dd01637f83a 100644
--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -387,7 +387,7 @@ static void save_restore_regs(struct bpf_jit *jit, int op)
  * Save registers and create stack frame if necessary.
  * See stack frame layout desription in "bpf_jit.h"!
  */
-static void bpf_jit_prologue(struct bpf_jit *jit)
+static void bpf_jit_prologue(struct bpf_jit *jit, bool is_classic)
 {
 	if (jit->seen & SEEN_TAIL_CALL) {
 		/* xc STK_OFF_TCCNT(4,%r15),STK_OFF_TCCNT(%r15) */
@@ -440,13 +440,15 @@ static void bpf_jit_prologue(struct bpf_jit *jit)
 		EMIT6_DISP_LH(0xe3000000, 0x0004, REG_SKB_DATA, REG_0,
 			      BPF_REG_1, offsetof(struct sk_buff, data));
 	}
-	/* BPF compatibility: clear A (%b0) and X (%b7) registers */
-	if (REG_SEEN(BPF_REG_A))
-		/* lghi %ba,0 */
-		EMIT4_IMM(0xa7090000, BPF_REG_A, 0);
-	if (REG_SEEN(BPF_REG_X))
-		/* lghi %bx,0 */
-		EMIT4_IMM(0xa7090000, BPF_REG_X, 0);
+	/* Clear A (%b0) and X (%b7) registers for converted BPF programs */
+	if (is_classic) {
+		if (REG_SEEN(BPF_REG_A))
+			/* lghi %ba,0 */
+			EMIT4_IMM(0xa7090000, BPF_REG_A, 0);
+		if (REG_SEEN(BPF_REG_X))
+			/* lghi %bx,0 */
+			EMIT4_IMM(0xa7090000, BPF_REG_X, 0);
+	}
 }
 
 /*
@@ -1232,7 +1234,7 @@ static int bpf_jit_prog(struct bpf_jit *jit, struct bpf_prog *fp)
 	jit->lit = jit->lit_start;
 	jit->prg = 0;
 
-	bpf_jit_prologue(jit);
+	bpf_jit_prologue(jit, fp->type == BPF_PROG_TYPE_UNSPEC);
 	for (i = 0; i < fp->len; i += insn_count) {
 		insn_count = bpf_jit_insn(jit, fp, i);
 		if (insn_count < 0)