[PATCH net-next 0/5] s390/bpf: recache skb->data/hlen for skb_vlan_push/pop

[PATCH net-next 0/5] s390/bpf: recache skb->data/hlen for skb_vlan_push/pop

[Michael Holzheu]

Hi Dave,

Here the s390 backend for Alexei's patch 4e10df9a60d9 ("bpf: introduce
bpf_skb_vlan_push/pop() helpers") plus two bugfixes and two minor
improvements.

The first patch "s390/bpf: clear correct BPF accumulator register" will
also go upstream via Martin's "fixes" branch.

Ok for you?

Regards,
Michael

Michael Holzheu (5):
  s390/bpf: clear correct BPF accumulator register
  s390/bpf: Fix multiple macro expansions
  s390/bpf: increase BPF_SIZE_MAX
  s390/bpf: Only clear A and X for converted BPF programs
  s390/bpf: recache skb->data/hlen for skb_vlan_push/pop

 arch/s390/net/bpf_jit.h      |  5 ++-
 arch/s390/net/bpf_jit_comp.c | 91 +++++++++++++++++++++++---------------------
 2 files changed, 52 insertions(+), 44 deletions(-)

-- 
2.3.8

[PATCH net-next 1/5] s390/bpf: clear correct BPF accumulator register

[Michael Holzheu]

Currently we assumed the following BPF to eBPF register mapping:

 - BPF_REG_A -> BPF_REG_7
 - BPF_REG_X -> BPF_REG_8

Unfortunately this mapping is wrong. The correct mapping is:

 - BPF_REG_A -> BPF_REG_0
 - BPF_REG_X -> BPF_REG_7

So clear the correct registers and use the BPF_REG_A and BPF_REG_X
macros instead of BPF_REG_0/7.

Fixes: 054623105728 ("s390/bpf: Add s390x eBPF JIT compiler backend")
Cc: stable@vger.kernel.org # 4.0+
Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
---
 arch/s390/net/bpf_jit_comp.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
index 79c731e..01ad166 100644
--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -448,13 +448,13 @@ 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 (%b7) and X (%b8) registers */
-	if (REG_SEEN(BPF_REG_7))
-		/* lghi %b7,0 */
-		EMIT4_IMM(0xa7090000, BPF_REG_7, 0);
-	if (REG_SEEN(BPF_REG_8))
-		/* lghi %b8,0 */
-		EMIT4_IMM(0xa7090000, BPF_REG_8, 0);
+	/* 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);
 }
 
 /*
-- 
2.3.8

[PATCH net-next 2/5] s390/bpf: Fix multiple macro expansions

[Michael Holzheu]

The EMIT6_DISP_LH macro passes the "disp" parameter to the _EMIT6_DISP_LH
macro. The _EMIT6_DISP_LH macro uses the "disp" parameter twice:

 unsigned int __disp_h = ((u32)disp) & 0xff000;
 unsigned int __disp_l = ((u32)disp) & 0x00fff;

The EMIT6_DISP_LH is used several times with EMIT_CONST_U64() as "disp"
parameter. Therefore always two constants are created per usage of
EMIT6_DISP_LH.

Fix this and add variable "__disp" to avoid multiple expansions.

Fixes: 054623105728 ("s390/bpf: Add s390x eBPF JIT compiler backend")
Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
---
 arch/s390/net/bpf_jit_comp.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
index 01ad166..de0f0bc 100644
--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -221,8 +221,9 @@ static inline void reg_set_seen(struct bpf_jit *jit, u32 b1)
 
 #define EMIT6_DISP_LH(op1, op2, b1, b2, b3, disp)		\
 ({								\
+	int __disp = (disp);					\
 	_EMIT6_DISP_LH(op1 | reg(b1, b2) << 16 |		\
-		       reg_high(b3) << 8, op2, disp);		\
+		       reg_high(b3) << 8, op2, __disp);		\
 	REG_SET_SEEN(b1);					\
 	REG_SET_SEEN(b2);					\
 	REG_SET_SEEN(b3);					\
-- 
2.3.8

Re: [PATCH net-next 2/5] s390/bpf: Fix multiple macro expansions

[Joe Perches]

On Tue, 2015-07-28 at 16:09 +0200, Michael Holzheu wrote:
> The EMIT6_DISP_LH macro passes the "disp" parameter to the _EMIT6_DISP_LH
> macro. The _EMIT6_DISP_LH macro uses the "disp" parameter twice:
> 
>  unsigned int __disp_h = ((u32)disp) & 0xff000;
>  unsigned int __disp_l = ((u32)disp) & 0x00fff;
> 
> The EMIT6_DISP_LH is used several times with EMIT_CONST_U64() as "disp"
> parameter. Therefore always two constants are created per usage of
> EMIT6_DISP_LH.
> 
> Fix this and add variable "__disp" to avoid multiple expansions.
> 
> Fixes: 054623105728 ("s390/bpf: Add s390x eBPF JIT compiler backend")
> Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
> ---
>  arch/s390/net/bpf_jit_comp.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
> index 01ad166..de0f0bc 100644
> --- a/arch/s390/net/bpf_jit_comp.c
> +++ b/arch/s390/net/bpf_jit_comp.c
> @@ -221,8 +221,9 @@ static inline void reg_set_seen(struct nbpf_jit *jit, u32 b1)
>  
>  #define EMIT6_DISP_LH(op1, op2, b1, b2, b3, disp)		\
>  ({								\
> +	int __disp = (disp);					\
>  	_EMIT6_DISP_LH(op1 | reg(b1, b2) << 16 |		\
> -		       reg_high(b3) << 8, op2, disp);		\
> +		       reg_high(b3) << 8, op2, __disp);		\
>  	REG_SET_SEEN(b1);					\
>  	REG_SET_SEEN(b2);					\
>  	REG_SET_SEEN(b3);					\

Perhaps it'd be better to change _EMIT6_DISP_LH
---
diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
index 3a15baa..409e206 100644
--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -205,8 +205,9 @@ static inline void reg_set_seen(struct bpf_jit *jit,
u32 b1)
 
 #define _EMIT6_DISP_LH(op1, op2, disp)				\
 ({								\
-	unsigned int __disp_h = ((u32)disp) & 0xff000;		\
-	unsigned int __disp_l = ((u32)disp) & 0x00fff;		\
+	u32 _disp = (u32)disp;					\
+	unsigned int __disp_h = _disp & 0xff000;		\
+	unsigned int __disp_l = _disp & 0x00fff;		\
 	_EMIT6(op1 | __disp_l, op2 | __disp_h >> 4);		\
 })
 

Re: [PATCH net-next 2/5] s390/bpf: Fix multiple macro expansions

[Michael Holzheu]

On Tue, 28 Jul 2015 20:13:41 -0700
Joe Perches <joe@perches.com> wrote:

> On Tue, 2015-07-28 at 16:09 +0200, Michael Holzheu wrote:
> > The EMIT6_DISP_LH macro passes the "disp" parameter to the _EMIT6_DISP_LH
> > macro. The _EMIT6_DISP_LH macro uses the "disp" parameter twice:
> > 
> >  unsigned int __disp_h = ((u32)disp) & 0xff000;
> >  unsigned int __disp_l = ((u32)disp) & 0x00fff;
> > 
> > The EMIT6_DISP_LH is used several times with EMIT_CONST_U64() as "disp"
> > parameter. Therefore always two constants are created per usage of
> > EMIT6_DISP_LH.
> > 
> > Fix this and add variable "__disp" to avoid multiple expansions.
> > 
> > Fixes: 054623105728 ("s390/bpf: Add s390x eBPF JIT compiler backend")
> > Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
> > ---
> >  arch/s390/net/bpf_jit_comp.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
> > index 01ad166..de0f0bc 100644
> > --- a/arch/s390/net/bpf_jit_comp.c
> > +++ b/arch/s390/net/bpf_jit_comp.c
> > @@ -221,8 +221,9 @@ static inline void reg_set_seen(struct nbpf_jit *jit, u32 b1)
> >  
> >  #define EMIT6_DISP_LH(op1, op2, b1, b2, b3, disp)		\
> >  ({								\
> > +	int __disp = (disp);					\
> >  	_EMIT6_DISP_LH(op1 | reg(b1, b2) << 16 |		\
> > -		       reg_high(b3) << 8, op2, disp);		\
> > +		       reg_high(b3) << 8, op2, __disp);		\
> >  	REG_SET_SEEN(b1);					\
> >  	REG_SET_SEEN(b2);					\
> >  	REG_SET_SEEN(b3);					\
> 
> Perhaps it'd be better to change _EMIT6_DISP_LH

Looks a bit better. I will send the updated patch.

Thanks!
Michael

> ---
> diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
> index 3a15baa..409e206 100644
> --- a/arch/s390/net/bpf_jit_comp.c
> +++ b/arch/s390/net/bpf_jit_comp.c
> @@ -205,8 +205,9 @@ static inline void reg_set_seen(struct bpf_jit *jit,
> u32 b1)
> 
>  #define _EMIT6_DISP_LH(op1, op2, disp)				\
>  ({								\
> -	unsigned int __disp_h = ((u32)disp) & 0xff000;		\
> -	unsigned int __disp_l = ((u32)disp) & 0x00fff;		\
> +	u32 _disp = (u32)disp;					\
> +	unsigned int __disp_h = _disp & 0xff000;		\
> +	unsigned int __disp_l = _disp & 0x00fff;		\
>  	_EMIT6(op1 | __disp_l, op2 | __disp_h >> 4);		\
>  })
> 
> 
> 

[PATCH net-next 3/5] s390/bpf: increase BPF_SIZE_MAX

[Michael Holzheu]

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>
---
 arch/s390/net/bpf_jit_comp.c | 15 +++------------
 1 file changed, 3 insertions(+), 12 deletions(-)

diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
index de0f0bc..bea5cfc 100644
--- a/arch/s390/net/bpf_jit_comp.c
+++ b/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)				\
 ({								\
 	unsigned int __disp_h = ((u32)disp) & 0xff000;		\
@@ -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 */
-- 
2.3.8

[PATCH net-next 4/5] s390/bpf: Only clear A and X for converted BPF programs

[Michael Holzheu]

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>
---
 arch/s390/net/bpf_jit_comp.c | 20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
index bea5cfc..a025ddc 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)
-- 
2.3.8

[PATCH net-next 5/5] s390/bpf: recache skb->data/hlen for skb_vlan_push/pop

[Michael Holzheu]

Allow eBPF programs attached to TC qdiscs call skb_vlan_push/pop
via helper functions. These functions may change skb->data/hlen.
This data is cached by s390 JIT to improve performance of ld_abs/ld_ind
instructions. Therefore after a change we have to reload the data.

In case of usage of skb_vlan_push/pop, in the prologue we store
the SKB pointer on the stack and restore it after BPF_JMP_CALL
to skb_vlan_push/pop.

Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
---
 arch/s390/net/bpf_jit.h      |  5 +++-
 arch/s390/net/bpf_jit_comp.c | 55 ++++++++++++++++++++++++++------------------
 2 files changed, 37 insertions(+), 23 deletions(-)

diff --git a/arch/s390/net/bpf_jit.h b/arch/s390/net/bpf_jit.h
index f6498ee..f010c93 100644
--- a/arch/s390/net/bpf_jit.h
+++ b/arch/s390/net/bpf_jit.h
@@ -36,6 +36,8 @@ extern u8 sk_load_word[], sk_load_half[], sk_load_byte[];
  *	      |   BPF stack   |     |
  *	      |		      |     |
  *	      +---------------+     |
+ *	      | 8 byte skbp   |     |
+ * R15+170 -> +---------------+     |
  *	      | 8 byte hlen   |     |
  * R15+168 -> +---------------+     |
  *	      | 4 byte align  |     |
@@ -51,11 +53,12 @@ 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.
  */
-#define STK_SPACE	(MAX_BPF_STACK + 8 + 4 + 4 + 160)
+#define STK_SPACE	(MAX_BPF_STACK + 8 + 8 + 4 + 4 + 160)
 #define STK_160_UNUSED	(160 - 12 * 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 */
+#define STK_OFF_SKBP	170	/* Offset of SKB pointer on stack */
 
 #define STK_OFF_R6	(160 - 11 * 8)	/* Offset of r6 on stack */
 #define STK_OFF_TCCNT	(160 - 12 * 8)	/* Offset of tail_call_cnt on stack */
diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
index a025ddc..ece46d4 100644
--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -53,6 +53,7 @@ struct bpf_jit {
 #define SEEN_LITERAL	8	/* code uses literals */
 #define SEEN_FUNC	16	/* calls C functions */
 #define SEEN_TAIL_CALL	32	/* code uses tail calls */
+#define SEEN_SKB_CHANGE	64	/* code changes skb data */
 #define SEEN_STACK	(SEEN_FUNC | SEEN_MEM | SEEN_SKB)
 
 /*
@@ -382,6 +383,26 @@ static void save_restore_regs(struct bpf_jit *jit, int op)
 }
 
 /*
+ * For SKB access %b1 contains the SKB pointer. For "bpf_jit.S"
+ * we store the SKB header length on the stack and the SKB data
+ * pointer in REG_SKB_DATA.
+ */
+static void emit_load_skb_data_hlen(struct bpf_jit *jit)
+{
+	/* Header length: llgf %w1,<len>(%b1) */
+	EMIT6_DISP_LH(0xe3000000, 0x0016, REG_W1, REG_0, BPF_REG_1,
+		      offsetof(struct sk_buff, len));
+	/* s %w1,<data_len>(%b1) */
+	EMIT4_DISP(0x5b000000, REG_W1, BPF_REG_1,
+		   offsetof(struct sk_buff, data_len));
+	/* stg %w1,ST_OFF_HLEN(%r0,%r15) */
+	EMIT6_DISP_LH(0xe3000000, 0x0024, REG_W1, REG_0, REG_15, STK_OFF_HLEN);
+	/* lg %skb_data,data_off(%b1) */
+	EMIT6_DISP_LH(0xe3000000, 0x0004, REG_SKB_DATA, REG_0,
+		      BPF_REG_1, offsetof(struct sk_buff, data));
+}
+
+/*
  * Emit function prologue
  *
  * Save registers and create stack frame if necessary.
@@ -421,25 +442,12 @@ static void bpf_jit_prologue(struct bpf_jit *jit, bool is_classic)
 			EMIT6_DISP_LH(0xe3000000, 0x0024, REG_W1, REG_0,
 				      REG_15, 152);
 	}
-	/*
-	 * For SKB access %b1 contains the SKB pointer. For "bpf_jit.S"
-	 * we store the SKB header length on the stack and the SKB data
-	 * pointer in REG_SKB_DATA.
-	 */
-	if (jit->seen & SEEN_SKB) {
-		/* Header length: llgf %w1,<len>(%b1) */
-		EMIT6_DISP_LH(0xe3000000, 0x0016, REG_W1, REG_0, BPF_REG_1,
-			      offsetof(struct sk_buff, len));
-		/* s %w1,<data_len>(%b1) */
-		EMIT4_DISP(0x5b000000, REG_W1, BPF_REG_1,
-			   offsetof(struct sk_buff, data_len));
-		/* stg %w1,ST_OFF_HLEN(%r0,%r15) */
+	if (jit->seen & SEEN_SKB)
+		emit_load_skb_data_hlen(jit);
+	if (jit->seen & SEEN_SKB_CHANGE)
+		/* stg %b1,ST_OFF_SKBP(%r0,%r15) */
 		EMIT6_DISP_LH(0xe3000000, 0x0024, REG_W1, REG_0, REG_15,
-			      STK_OFF_HLEN);
-		/* lg %skb_data,data_off(%b1) */
-		EMIT6_DISP_LH(0xe3000000, 0x0004, REG_SKB_DATA, REG_0,
-			      BPF_REG_1, offsetof(struct sk_buff, data));
-	}
+			      STK_OFF_SKBP);
 	/* Clear A (%b0) and X (%b7) registers for converted BPF programs */
 	if (is_classic) {
 		if (REG_SEEN(BPF_REG_A))
@@ -967,10 +975,6 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp, int i
 		 */
 		const u64 func = (u64)__bpf_call_base + imm;
 
-		if (bpf_helper_changes_skb_data((void *)func))
-			/* TODO reload skb->data, hlen */
-			return -1;
-
 		REG_SET_SEEN(BPF_REG_5);
 		jit->seen |= SEEN_FUNC;
 		/* lg %w1,<d(imm)>(%l) */
@@ -980,6 +984,13 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp, int i
 		EMIT2(0x0d00, REG_14, REG_W1);
 		/* lgr %b0,%r2: load return value into %b0 */
 		EMIT4(0xb9040000, BPF_REG_0, REG_2);
+		if (bpf_helper_changes_skb_data((void *)func)) {
+			jit->seen |= SEEN_SKB_CHANGE;
+			/* lg %b1,ST_OFF_SKBP(%r15) */
+			EMIT6_DISP_LH(0xe3000000, 0x0004, BPF_REG_1, REG_0,
+				      REG_15, STK_OFF_SKBP);
+			emit_load_skb_data_hlen(jit);
+		}
 		break;
 	}
 	case BPF_JMP | BPF_CALL | BPF_X:
-- 
2.3.8

Re: [PATCH net-next 5/5] s390/bpf: recache skb->data/hlen for skb_vlan_push/pop

[Alexei Starovoitov]

On 7/28/15 7:10 AM, Michael Holzheu wrote:
> Allow eBPF programs attached to TC qdiscs call skb_vlan_push/pop
> via helper functions. These functions may change skb->data/hlen.
> This data is cached by s390 JIT to improve performance of ld_abs/ld_ind
> instructions. Therefore after a change we have to reload the data.
>
> In case of usage of skb_vlan_push/pop, in the prologue we store
> the SKB pointer on the stack and restore it after BPF_JMP_CALL
> to skb_vlan_push/pop.
>
> Signed-off-by: Michael Holzheu<holzheu@linux.vnet.ibm.com>

Thanks!
Acked-by: Alexei Starovoitov <ast@plumgrid.com>